ORCID Profile
0000-0001-7950-8699
Current Organisations
Princeton University
,
Walter and Eliza Hall Institute of Medical Research
,
Australian National University
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Infectious Agents | Medical Parasitology | Medical Parasitology | Medical Microbiology | Gene Expression | Structural Biology (incl. Macromolecular Modelling) | Microbiology |
Infectious diseases | Expanding Knowledge in the Biological Sciences | Infectious Diseases
Publisher: Public Library of Science (PLoS)
Date: 04-12-2020
DOI: 10.1371/JOURNAL.PONE.0238010
Abstract: Multiplexed bead-based assays that use Luminex ® xMAP ® technology have become popular for measuring antibodies against proteins of interest in many fields, including malaria and more recently SARS-CoV-2/COVID-19. There are currently two formats that are widely used: non-magnetic beads or magnetic beads. Data are lacking regarding the comparability of results obtained using these two types of beads, and for assays run on different instruments. Whilst non-magnetic beads can only be run on flow-based instruments (such as the Luminex ® 100/200™ or Bio-Plex ® 200), magnetic beads can be run on both these and the newer MAGPIX ® instruments. In this study we utilized a panel of purified recombinant Plasmodium vivax proteins and s les from malaria-endemic areas to measure P . vivax -specific IgG responses using different combinations of beads and instruments. We directly compared: i) non-magnetic versus magnetic beads run on a Bio-Plex ® 200, ii) magnetic beads run on the Bio-Plex ® 200 versus MAGPIX ® and iii) non-magnetic beads run on a Bio-Plex ® 200 versus magnetic beads run on the MAGPIX ® . We also performed an external comparison of our optimized assay. We observed that IgG antibody responses, measured against our panel of P . vivax proteins, were moderately-strongly correlated in all three of our comparisons (pearson r .5 for 18/19 proteins), however higher amounts of protein were required for coupling to magnetic beads. Our external comparison indicated that results generated in different laboratories using the same coupled beads are also highly comparable (pearson r .7), particularly if a reference standard curve is used.
Publisher: Elsevier BV
Date: 09-2005
DOI: 10.1016/J.CELL.2005.07.010
Abstract: The meiotic recombination checkpoint delays gamete precursors in G2 until DNA breaks created during recombination are repaired and chromosome structure has been restored. Here, we show that the FK506 binding protein Fpr3 prevents premature adaptation to damage and thus serves to maintain recombination checkpoint activity. Impaired checkpoint function is observed both in cells lacking FPR3 and in cells treated with rapamycin, a small molecule inhibitor that binds to the proline isomerase (PPIase) domain of Fpr3. FPR3 functions in the checkpoint through controlling protein phosphatase 1 (PP1). Fpr3 interacts with PP1 through its PPIase domain, regulates PP1 localization, and counteracts the activity of PP1 in vivo. Our findings define a branch of the recombination checkpoint involved in the adaptation to persistent chromosomal damage and a critical function for FK506 binding proteins during meiosis.
Publisher: Cold Spring Harbor Laboratory
Date: 29-10-2021
DOI: 10.1101/2021.10.27.465224
Abstract: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection causing coronavirus disease 2019 (COVID-19) has caused a global health crisis. The primary site of infection is in the respiratory tract but the virus has been associated with a variety of complications involving the gastrointestinal and cardiovascular systems. Since the virus affects a variety of tissue types, there has been interest in understanding SARS-CoV-2 infection in early development and the placenta. ACE2 and TMPRSS2, two genes that are critical for SARS-CoV-2 virus entry are expressed in placenta-specific cell types including extravillous trophoblasts (EVTs) and especially, syncytiotrophoblasts (STs). The potential of SARS-CoV-2 to infect these placental cells and its effect on placental development and function is still unclear. Furthermore, it is crucial to understand the possible mechanism of vertical transmission of SARS-CoV-2 through the placenta. Here, we developed an in vitro model of SARS-CoV-2 infection of placental cell types using induced trophoblast stem cells (iTSCs). This model allowed us to show that STs but not EVTs are infected. Importantly, infected STs lack the expression of key differentiation genes, lack typically observed differentiated morphology and produce significantly lower human chorionic gonadotropin (HCG) compared to non-infected controls. We also show that an anti-ACE2 antibody prevents SARS-CoV-2 infection and restores normal ST differentiation and function. We highlight the establishment of a platform to study SARS-CoV-2 infection in early placental cell types, which will facilitate investigation of antiviral therapy to protect the placenta during early pregnancy and development.
Publisher: Wiley
Date: 26-09-2019
DOI: 10.1111/IMR.12802
Publisher: Springer Science and Business Media LLC
Date: 21-01-2002
Abstract: Telomeres are the natural ends of eukaryotic chromosomes. In most organisms, telomeres consist of simple, repeated DNA with the strand running 5' to 3' towards the end of the chromosome being rich in G residues. In cases where the very end of the chromosome has been examined, the G-strand is extended to form a short, single stranded tail. The chromatin structure of telomeric regions often has features that distinguish them from other parts of the genome. Because telomeres protect chromosome ends from degradation and end-to-end fusions and prevent the loss of terminal DNA by serving as a substrate for telomerase, they are essential for the stable maintenance of eukaryotic chromosomes. In addition to their essential functions, telomeres in erse organisms are specialized sites for gene expression. Transcription of genes located next to telomeres is repressed, a phenomenon termed telomere position effect (TPE). TPE is best characterized in the yeast Saccharomyces cerevisiae. This article will focus on the silencing properties of Saccharomyces telomeres and end with speculation on the role of TPE in yeasts and other organisms.
Publisher: Public Library of Science (PLoS)
Date: 27-02-2015
Publisher: Springer Science and Business Media LLC
Date: 13-07-2020
Publisher: Elsevier BV
Date: 11-2022
Publisher: Cold Spring Harbor Laboratory
Date: 07-08-2020
DOI: 10.1101/2020.08.07.20169862
Abstract: To achieve malaria elimination, new tools are required to explicitly target Plasmodium vivax . Recently, a novel panel of P. vivax proteins were identified and validated as serological markers for detecting recent exposure to P. vivax within the last 9 months. In order to improve the sensitivity and specificity of these markers, IgM in addition to IgG antibody responses were assessed to a down-selected panel of 20 P. vivax proteins. IgM was tested using archival plasma s les from observational cohort studies conducted in malaria-endemic regions of Thailand and Brazil. IgM responses to these proteins generally had poorer classification performance than IgG.
Publisher: Springer Science and Business Media LLC
Date: 12-12-2018
DOI: 10.1038/S41586-018-0779-6
Abstract: Plasmodium falciparum causes the severe form of malaria that has high levels of mortality in humans. Blood-stage merozoites of P. falciparum invade erythrocytes, and this requires interactions between multiple ligands from the parasite and receptors in hosts. These interactions include the binding of the Rh5-CyRPA-Ripr complex with the erythrocyte receptor basigin
Publisher: Hindawi Limited
Date: 07-10-2020
DOI: 10.1111/CMI.13270
Publisher: Hindawi Limited
Date: 24-04-2019
DOI: 10.1111/CMI.13030
Publisher: Hindawi Limited
Date: 08-09-2019
DOI: 10.1111/CMI.13110
Publisher: Springer Science and Business Media LLC
Date: 04-03-2022
DOI: 10.1186/S12936-022-04085-X
Abstract: Plasmodium vivax is emerging as the dominant and prevalent species causing malaria in near-elimination settings outside of Africa. Hypnozoites, the dormant liver stage parasite of P. vivax , are undetectable to any currently available diagnostic test, yet are a major reservoir for transmission. Advances have been made to harness the naturally acquired immune response to identify recent exposure to P. vivax blood-stage parasites and, therefore, infer the presence of hypnozoites. This in-development diagnostic is currently able to detect infections within the last 9-months with 80% sensitivity and 80% specificity. Further work is required to optimize protein expression and protein constructs used for antibody detection. The antibody response against the top performing predictor of recent infection, P. vivax reticulocyte binding protein 2b (PvRBP2b), was tested against multiple fragments of different sizes and from different expression systems. The IgG induced against the recombinant PvRBP2b fragments in P. vivax infected in iduals was measured at the time of infection and in a year-long observational cohort both conducted in Thailand. The antibody responses to some but not all different sized fragments of PvRBP2b protein are highly correlated with each other, significantly higher 1-week post- P. vivax infection, and show potential for use as predictors of recent P. vivax infection. To achieve P. vivax elimination goals, novel diagnostics are required to aid in detection of hidden parasite reservoirs. PvRBP2b was previously shown to be the top candidate for single-antigen classification of recent P. vivax exposure and here, it is concluded that several alternative recombinant PvRBP2b fragments can achieve equal sensitivity and specificity at predicting recent P. vivax exposure.
Publisher: Elsevier BV
Date: 05-2007
DOI: 10.1016/J.IJPARA.2006.11.006
Abstract: The rif gene family is the largest multi-gene family in the malaria parasite Plasmodium falciparum. The gene products of rif genes, rifins, are clonally variant and transported to the surface of the infected erythrocyte where they are targets of the human immune response. Maximal rif transcription occurs during the late ring to early trophozoite stages of the intra-erythrocytic cycle. The factors involved in the transcriptional activation and repression of rif genes are not known. In this paper, we characterize several DNA elements involved in the regulation of rif transcription. We identify the upstream region that contains a functional promoter and the transcriptional start site of a rif gene. In addition, we identify two distinct regions within the rif upstream region involved in the transcriptional repression of these genes. These repressor sites are bound by nuclear protein factors expressed in different stages of the Plasmodium life cycle. We propose that the differential timing of binding provides a mechanism for the temporal repression of rif genes. In addition, we find that transcription profiles of upsA var genes and their neighbouring rif genes are unlinked.
Publisher: Public Library of Science (PLoS)
Date: 20-09-2012
Publisher: Cold Spring Harbor Laboratory
Date: 11-07-2020
DOI: 10.1101/2020.07.11.191494
Abstract: The remarkable deformability of red blood cells (RBCs) depends on the viscoelasticity of the plasma membrane and cell contents and the surface area to volume (SA:V) ratio however, it remains unclear which of these factors is the key determinant for passage through small capillaries. We used a microfluidic device to examine the traversal of normal, stiffened, swollen, parasitised and immature RBCs. We show that dramatic stiffening of RBCs had no measurable effect on their ability to traverse small channels. By contrast, a moderate decrease in the SA:V ratio had a marked effect on the equivalent cylinder diameter that is traversable by RBCs of similar stiffness. We developed a finite element model that provides a coherent rationale for the experimental observations, based on the nonlinear mechanical behaviour of the RBC membrane skeleton. We conclude that the SA:V ratio should be given more prominence in studies of RBC pathologies.
Publisher: Springer Science and Business Media LLC
Date: 21-07-2023
DOI: 10.1007/S00430-023-00773-W
Abstract: Emerging SARS-CoV-2 variants, notably Omicron, continue to remain a formidable challenge to worldwide public health. The SARS-CoV-2 receptor-binding domain (RBD) is a hotspot for mutations, reflecting its critical role at the ACE2 interface during viral entry. Here, we comprehensively investigated the impact of RBD mutations, including 5 variants of concern (VOC) or interest—including Omicron (BA.2)—and 33 common point mutations, both on IgG recognition and ACE2-binding inhibition, as well as FcγRIIa- and FcγRIIIa-binding antibodies, in plasma from two-dose BNT162b2-vaccine recipients and mild-COVID-19 convalescent subjects obtained during the first wave using a custom-designed bead-based 39-plex array. IgG-recognition and FcγR-binding antibodies were decreased against the RBD of Beta and Omicron, as well as point mutation G446S, found in several Omicron sub-variants as compared to wild type. Notably, while there was a profound decrease in ACE2 inhibition against Omicron, FcγR-binding antibodies were less affected, suggesting that Fc functional antibody responses may be better retained against the RBD of Omicron in comparison to neutralization. Furthermore, while measurement of RBD–ACE2-binding affinity via biolayer interferometry showed that all VOC RBDs have enhanced affinity to human ACE2, we demonstrate that human ACE2 polymorphisms, E35K (rs1348114695) has reduced affinity to VOCs, while K26R (rs4646116) and S19P (rs73635825) have increased binding kinetics to the RBD of VOCs, potentially affecting virus–host interaction and, thereby, host susceptibility. Collectively, our findings provide in-depth coverage of the impact of RBD mutations on key facets of host–virus interactions.
Publisher: Frontiers Media SA
Date: 10-01-2023
Publisher: Cold Spring Harbor Laboratory
Date: 11-12-2021
DOI: 10.1101/2021.12.09.21266664
Abstract: Serological exposure markers are a promising tool for surveillance and targeted interventions for Plasmodium vivax malaria. P. vivax is closely related to the zoonotic parasite P. knowlesi , which also infects humans. P. vivax and P. knowlesi are co-endemic across much of South East Asia, making it important to design P. vivax serological markers that minimise cross-reactivity in this region. Our objective was to determine the degree of IgG antibody cross-reactivity against a panel of P. vivax serological markers in s les from human participants with P. knowlesi malaria. We observed higher levels of IgG antibody reactivity against P. vivax proteins that had high levels of sequence identity with their P. knowlesi ortholog. IgG reactivity peaked at 7 days post P. knowlesi infection and was short-lived, with minimal responses detected at 1-year post-infection. Using these data, we designed a panel of 8 P. vivax proteins with low-levels of cross-reactivity with P. knowlesi . This panel was able to accurately classify recent P. vivax infections whilst reducing misclassification of recent P. knowlesi infections.
Publisher: eLife Sciences Publications, Ltd
Date: 26-09-2017
DOI: 10.7554/ELIFE.28673
Abstract: The study of antigenic targets of naturally-acquired immunity is essential to identify and prioritize antigens for further functional characterization. We measured total IgG antibodies to 38 P. vivax antigens, investigating their relationship with prospective risk of malaria in a cohort of 1–3 years old Papua New Guinean children. Using simulated annealing algorithms, the potential protective efficacy of antibodies to multiple antigen-combinations, and the antibody thresholds associated with protection were investigated for the first time. High antibody levels to multiple known and newly identified proteins were strongly associated with protection (IRR 0.44–0.74, p .001–0.041). Among five-antigen combinations with the strongest protective effect ( %), EBP, DBPII, RBP1a, CyRPA, and PVX_081550 were most frequently identified several of them requiring very low antibody levels to show a protective association. These data identify in idual antigens that should be prioritized for further functional testing and establish a clear path to testing a multicomponent P. vivax vaccine.
Publisher: Proceedings of the National Academy of Sciences
Date: 20-09-2010
Abstract: Plasmodium falciparum is responsible for the most severe form of malaria disease in humans, causing more than 1 million deaths each year. As an obligate intracellular parasite, P. falciparum ’s ability to invade erythrocytes is essential for its survival within the human host. P. falciparum invades erythrocytes using multiple host receptor–parasite ligand interactions known as invasion pathways. Here we show that CR1 is the host erythrocyte receptor for PfRh4, a major P. falciparum ligand essential for sialic acid–independent invasion. PfRh4 and CR1 interact directly, with a K d of 2.9 μM. PfRh4 binding is strongly correlated with the CR1 level on the erythrocyte surface. Parasite invasion via sialic acid–independent pathways is reduced in low-CR1 erythrocytes due to limited availability of this receptor on the surface. Furthermore, soluble CR1 can competitively block binding of PfRh4 to the erythrocyte surface and specifically inhibit sialic acid–independent parasite invasion. These results demonstrate that CR1 is an erythrocyte receptor used by the parasite ligand PfRh4 for P. falciparum invasion.
Publisher: Elsevier BV
Date: 09-2015
DOI: 10.1016/J.MOLIMM.2015.03.006
Abstract: Malaria remains one of the world's deadliest diseases. Plasmodium falciparum is responsible for the most severe and lethal form of human malaria. P. falciparum's life cycle involves two obligate hosts: human and mosquito. From initial entry into these hosts, malaria parasites face the onslaught of the first line of host defence, the complement system. In this review, we discuss the complex interaction between complement and malaria infection in terms of hosts immune responses, parasite survival and pathogenesis of severe forms of malaria. We will focus on the role of complement receptor 1 and its associated polymorphisms in malaria immune complex clearance, as a mediator of parasite rosetting and as an entry receptor for P. falciparum invasion. Complement evasion strategies of P. falciparum parasites will also be highlighted. The sexual forms of the malaria parasites recruit the soluble human complement regulator Factor H to evade complement-mediated killing within the mosquito host. A novel evasion strategy is the deployment of parasite organelles to ert complement attack from infective blood stage parasites. Finally we outline the future challenge to understand the implications of these exploitation mechanisms in the interplay between successful infection of the host and pathogenesis observed in severe malaria.
Publisher: eLife Sciences Publications, Ltd
Date: 22-02-2017
DOI: 10.7554/ELIFE.21083
Abstract: The most lethal form of malaria in humans is caused by Plasmodium falciparum. These parasites invade erythrocytes, a complex process involving multiple ligand-receptor interactions. The parasite makes initial contact with the erythrocyte followed by dramatic deformations linked to the function of the Erythrocyte binding antigen family and P. falciparum reticulocyte binding-like families. We show EBA-175 mediates substantial changes in the deformability of erythrocytes by binding to glycophorin A and activating a phosphorylation cascade that includes erythrocyte cytoskeletal proteins resulting in changes in the viscoelastic properties of the host cell. TRPM7 kinase inhibitors FTY720 and waixenicin A block the changes in the deformability of erythrocytes and inhibit merozoite invasion by directly inhibiting the phosphorylation cascade. Therefore, binding of P. falciparum parasites to the erythrocyte directly activate a signaling pathway through a phosphorylation cascade and this alters the viscoelastic properties of the host membrane conditioning it for successful invasion.
Publisher: Oxford University Press (OUP)
Date: 22-05-2021
DOI: 10.1093/OFID/OFAB228
Abstract: To achieve malaria elimination, new tools are required to explicitly target Plasmodium vivax. Recently, a novel panel of P. vivax proteins were identified and validated as serological markers for detecting recent exposure to P. vivax within the last 9 months. In order to improve the sensitivity and specificity of these markers, immunoglobulin M (IgM) in addition to immunoglobulin G (IgG) antibody responses were compared with a down-selected panel of 20 P. vivax proteins. IgM was tested using archival plasma s les from observational cohort studies conducted in malaria-endemic regions of Thailand and Brazil. IgM responses to these proteins generally had poorer classification performance than IgG.
Publisher: Oxford University Press (OUP)
Date: 14-01-2008
Abstract: Alveolates are a recently recognized group of unicellular eukaryotes that unites disparate protists including apicomplexan parasites (which cause malaria and toxoplasmosis), dinoflagellate algae (which cause red tides and are symbionts in many corals), and ciliates (which are microscopic predators and common rumen symbionts). Gene sequence trees provide robust support for the alveolate alliance, but beyond the common presence of membranous sacs (alveoli) subtending the plasma membrane, the group has no unifying morphological feature. We describe a family of proteins, alveolins, associated with these membranous sacs in apicomplexa, dinoflagellates, and ciliates. Alveolins contain numerous simple peptide repeats and are encoded by multigene families. We generated antibodies against a peptide motif common to all alveolins and identified a range of apparently abundant proteins in apicomplexa, dinoflagellates, and ciliates. Immunolocalization reveals that alveolins are associated exclusively with the cortical regions of apicomplexa, dinoflagellates, and ciliates where the alveolar sacs occur. Alveolins are the first molecular nexus between the unifying structures that defines this eukaryotic group. They provide an excellent opportunity to explore the exceptional compartment that was apparently the key to a remarkable ersification of unique protists that occupy a wide array of lifestyle niches.
Publisher: Elsevier BV
Date: 08-2210
DOI: 10.1016/J.CHOM.2017.07.003
Abstract: Plasmodium species cause malaria by proliferating in human erythrocytes. Invasion of immunologically privileged erythrocytes provides a relatively protective niche as well as access to a rich source of nutrients. Plasmodium spp. target erythrocytes of different ages, but share a common mechanism of invasion. Specific engagement of erythrocyte receptors defines target cell tropism, activating downstream events and resulting in the physical penetration of the erythrocyte, powered by the parasite's actinomyosin-based motor. Here we review the latest in our understanding of the molecular composition of this highly complex and fascinating biological process.
Publisher: Elsevier BV
Date: 2012
Abstract: The global agenda for malaria eradication would benefit from development of a highly efficacious vaccine that protects against disease and interrupts transmission of Plasmodium falciparum. It is likely that such a vaccine will be multi-component, with antigens from different stages of the parasite life cycle. In this review, inclusion of blood stage antigens in such a vaccine is discussed. Erythrocyte binding-like (EBL) and P. falciparum reticulocyte binding-like (PfRh) proteins are reviewed with respect to their function in erythrocyte invasion, their role in eliciting antibodies contributing to protective immunity and reduction of invasion, leading subsequently to inhibition of parasite multiplication.
Publisher: Elsevier BV
Date: 02-2017
DOI: 10.1016/J.IJPARA.2016.09.006
Abstract: Plasmodium vivax parasites cause the majority of malaria cases outside Africa, and are increasingly being acknowledged as a cause of severe disease. The unique attributes of P. vivax biology, particularly the capacity of the dormant liver stage, the hypnozoite, to maintain blood-stage infections even in the absence of active transmission, make blood-stage vaccines particularly attractive for this species. However, P. vivax vaccine development remains resolutely in first gear, with only a single blood-stage candidate having been evaluated in any depth. Experience with Plasmodium falciparum suggests that a much broader search for new candidates and a deeper understanding of high priority targets will be required to make significant advances. This review discusses some of the particular challenges of P. vivax blood-stage vaccine development, highlighting both recent advances and key remaining barriers to overcome in order to move development forward.
Publisher: Springer Science and Business Media LLC
Date: 09-03-2022
DOI: 10.1186/S12916-022-02281-9
Abstract: Plasmodium vivax ( P. vivax ) is the dominant Plasmodium spp. causing the disease malaria in low-transmission regions outside of Africa. These regions often feature high proportions of asymptomatic patients with sub-microscopic parasitaemia and relapses. Naturally acquired antibody responses are induced after Plasmodium infection, providing partial protection against high parasitaemia and clinical episodes. However, previous work has failed to address the presence and maintenance of such antibody responses to P. vivax particularly in low-transmission regions. We followed 34 patients in western Thailand after symptomatic P. vivax infections to monitor antibody kinetics over 9 months, during which no recurrent infections occurred. We assessed total IgG, IgG subclass and IgM levels to up to 52 P. vivax proteins every 2–4 weeks using a multiplexed Luminex® assay and identified protein-specific variation in antibody longevity. Mathematical modelling was used to generate the estimated half-life of antibodies, long-, and short-lived antibody-secreting cells. Generally, an increase in antibody level was observed within 1-week post symptomatic infection, followed by an exponential decay of different rates. We observed mostly IgG1 dominance and IgG3 sub-dominance in this population. IgM responses followed similar kinetic patterns to IgG, with some proteins unexpectedly inducing long-lived IgM responses. We also monitored antibody responses against 27 IgG-immunogenic antigens in 30 asymptomatic in iduals from a similar region. Our results demonstrate that most antigens induced robust and long-lived total IgG responses following asymptomatic infections in the absence of (detected) boosting infections. Our work provides new insights into the development and maintenance of naturally acquired immunity to P. vivax and will guide the potential use of serology to indicate immune status and/or identify populations at risk.
Publisher: Frontiers Media SA
Date: 29-06-2021
DOI: 10.3389/FMICB.2021.643501
Abstract: Thailand is aiming for malaria elimination by the year 2030. However, the high proportion of asymptomatic infections and the presence of the hidden hypnozoite stage of Plasmodium vivax are impeding these efforts. We hypothesized that a validated surveillance tool utilizing serological markers of recent exposure to P. vivax infection could help to identify areas of ongoing transmission. The objective of this exploratory study was to assess the ability of P. vivax serological exposure markers to detect residual transmission “hot-spots” in Western Thailand. Total IgG levels were measured against a panel of 23 candidate P. vivax serological exposure markers using a multiplexed bead-based assay. A total of 4,255 plasma s les from a cross-sectional survey conducted in 2012 of endemic areas in the Kanchanaburi and Ratchaburi provinces were assayed. We compared IgG levels with multiple epidemiological factors that are associated with an increased risk of P. vivax infection in Thailand, including age, gender, and spatial location, as well as Plasmodium infection status itself. IgG levels to all proteins were significantly higher in the presence of a P. vivax infection ( n = 144) ( T -test, p & 0.0001). Overall seropositivity rates varied from 2.5% (PVX_097625, merozoite surface protein 8) to 16.8% (PVX_082670, merozoite surface protein 7), with 43% of in iduals seropositive to at least 1 protein. Higher IgG levels were associated with older age (& years, p & 0.05) and males (17/23 proteins, p & 0.05), supporting the paradigm that men have a higher risk of infection than females in this setting. We used a Random Forests algorithm to predict which in iduals had exposure to P. vivax parasites in the last 9-months, based on their IgG antibody levels to a panel of eight previously validated P. vivax proteins. Spatial clustering was observed at the village and regional level, with a moderate correlation between PCR prevalence and sero-prevalence as predicted by the algorithm. Our data provides proof-of-concept for application of such surrogate markers as evidence of recent exposure in low transmission areas. These data can be used to better identify geographical areas with asymptomatic infection burdens that can be targeted in elimination c aigns.
Publisher: Elsevier BV
Date: 07-2001
DOI: 10.1016/S1097-2765(01)00287-8
Abstract: The left telomere of Saccharomyces chromosome VII was often localized near the nuclear periphery, even in cells lacking the silencing proteins Sir3 or Hdf1. This association was lost in late mitotic cells and when transcription was induced through the telomeric tract. Although in silencing competent cells there was no correlation between the fraction of cells in which a telomeric gene was repressed and the fraction of cells in which it was localized to the periphery, no condition was found where the telomere was both silenced and away from the periphery. We conclude that localization of a telomere to the nuclear periphery is not sufficient for transcriptional repression nor does it affect the stability function of yeast telomeres.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 05-01-2018
Abstract: Human malaria is caused by half a dozen species of Plasmodium protozoan parasites, each with distinctive biology. P. vivax , which causes relapsing malaria, specifically parasitizes immature red blood cells called reticulocytes. Gruszczyk et al. identified TfR1 (host transferrin receptor 1) as an alternative receptor for P. vivax . TfR1 binds to a specific P. vivax surface protein. However, the parasite that causes cerebral malaria, P. falciparum , does not share TfR1 as a receptor: P. falciparum could still infect cells in which TfR1 expression was knocked down, but P. vivax could not. Monoclonal antibodies to the P. vivax protein successfully hindered P. vivax infection of red blood cells. Science , this issue p. 48
Publisher: Elsevier BV
Date: 10-2015
Publisher: Proceedings of the National Academy of Sciences
Date: 19-12-2000
Abstract: The tobacco N gene is a member of the Toll-interleukin-1 receptor/nucleotide-binding site/leucine-rich repeat (TIR-NBS-LRR) class of plant resistance ( R ) genes and confers resistance to tobacco mosaic virus (TMV). We investigated the importance of specific domains of N in inducing TMV resistance, by examining various N deletion and point mutations that introduce single amino acid substitution mutants in vivo . Our deletion analysis suggests that the TIR, NBS, and LRR domains play an indispensable role in the induction of resistance responses against TMV. We show that amino acids conserved among the Toll/IL-1R lant R gene TIR domain and NBS-containing proteins play a critical role in N -mediated TMV resistance. Some loss-of-function N alleles such as the TIR deletion and point mutations in the NBS (G216A/E/V/R, G218R, G219D, K222E/N, and T223A/N) interfere with the wild-type N function and behave like dominant negative mutations. These F 1 plants mount a hypersensitive response (HR) that is indistinguishable from that of the wild-type N plants, yet TMV was able to move systemically, causing a systemic hypersensitive response (SHR). Many amino acid substitutions in the TIR, NBS, and LRR domains of N lead to a partial loss-of-function phenotype. These mutant plants mount delayed HR compared with the wild-type N plants and fail to contain the virus to the infection site. In addition, some partial loss-of-function alleles (W82S/A, W141S/A, G218V/S, and G219V) interfere with the wild-type N function, leading to SHR. The partial loss-of-function and dominant negative mutant alleles described in this report will be useful in furthering our understanding of the TIR-NBS-LRR class of R genes.
Publisher: Springer Science and Business Media LLC
Date: 13-07-2023
DOI: 10.1038/S41556-023-01182-0
Abstract: SARS-CoV-2 infection causes COVID-19. Several clinical reports have linked COVID-19 during pregnancy to negative birth outcomes and placentitis. However, the pathophysiological mechanisms underpinning SARS-CoV-2 infection during placentation and early pregnancy are not clear. Here, to shed light on this, we used induced trophoblast stem cells to generate an in vitro early placenta infection model. We identified that syncytiotrophoblasts could be infected through angiotensin-converting enzyme 2 (ACE2). Using a co-culture model of vertical transmission, we confirmed the ability of the virus to infect syncytiotrophoblasts through a previous endometrial cell infection. We further demonstrated transcriptional changes in infected syncytiotrophoblasts that led to impairment of cellular processes, reduced secretion of HCG hormone and morphological changes vital for syncytiotrophoblast function. Furthermore, different antibody strategies and antiviral drugs restore these impairments. In summary, we have established a scalable and tractable platform to study early placental cell types and highlighted its use in studying strategies to protect the placenta.
Publisher: American Society for Microbiology
Date: 03-2019
DOI: 10.1128/AAC.01804-18
Abstract: A series of 4-amino 2-anilinoquinazolines optimized for activity against the most lethal malaria parasite of humans, Plasmodium falciparum , was evaluated for activity against other human Plasmodium parasites and related apicomplexans that infect humans and animals. Four of the most promising compounds from the 4-amino 2-anilinoquinazoline series were equally as effective against the asexual blood stages of the zoonotic P. knowlesi , suggesting that they could also be effective against the closely related P. vivax , another important human pathogen.
Publisher: Springer Science and Business Media LLC
Date: 20-06-2019
DOI: 10.1038/S41598-019-45228-6
Abstract: Plasmodium vivax parasites preferentially invade reticulocyte cells in a multistep process that is still poorly understood. In this study, we used ex vivo invasion assays and population genetic analyses to investigate the involvement of complement receptor 1 (CR1) in P . vivax invasion. First, we observed that P . vivax invasion of reticulocytes was consistently reduced when CR1 surface expression was reduced through enzymatic cleavage, in the presence of naturally low-CR1-expressing cells compared with high-CR1-expressing cells, and with the addition of soluble CR1, a known inhibitor of P . falciparum invasion. Immuno-precipitation experiments with P . vivax Reticulocyte Binding Proteins showed no evidence of complex formation. In addition, analysis of CR1 genetic data for worldwide human populations with different exposure to malaria parasites show significantly higher frequency of CR1 alleles associated with low receptor expression on the surface of RBCs and higher linkage disequilibrium in human populations exposed to P . vivax malaria compared with unexposed populations. These results are consistent with a positive selection of low-CR1-expressing alleles in vivax-endemic areas. Collectively, our findings demonstrate that CR1 availability on the surface of RBCs modulates P . vivax invasion. The identification of new molecular interactions is crucial to guiding the rational development of new therapeutic interventions against vivax malaria.
Publisher: Springer Science and Business Media LLC
Date: 27-06-2018
DOI: 10.1038/S41586-018-0249-1
Abstract: Plasmodium vivax is the most widely distributed malaria parasite that infects humans
Publisher: Elsevier BV
Date: 2014
Publisher: Springer Science and Business Media LLC
Date: 22-07-2021
DOI: 10.1038/S41564-021-00939-3
Abstract: More than one-third of the world's population is exposed to Plasmodium vivax malaria, mainly in Asia
Publisher: American Society of Tropical Medicine and Hygiene
Date: 03-05-2023
Abstract: As malaria control and elimination efforts r up in Ethiopia, more sensitive tools for assessing exposure to coendemic Plasmodium falciparum and Plasmodium vivax are needed to accurately characterize malaria risk and epidemiology. Serological markers have been increasingly explored as cost-effective tools for measuring transmission intensity and evaluating intervention effectiveness. The objectives of this study were to evaluate the efficacy of a panel of 10 serological markers as a proxy for malaria exposure and to determine underlying risk factors of seropositivity. We conducted cross-sectional surveys in two sites of contrasting malaria transmission intensities in southwestern Ethiopia: Arjo in Oromia Region (low transmission) and Gambella in Gambella Regional State (moderate transmission). We measured antibody reactivity against six P. falciparum (AMA-1, CSP, EBA175RIII-V, MSP-1 42 , MSP-3, RH2ab) and four P. vivax (DBPII[Sal1], EBP2, MSP-1 19 , RBP2b) targets. We used mixed effects logistic regressions to assess predictors of seropositivity. Plasmodium spp. infection prevalence by quantitative polymerase chain reaction was 1.36% in Arjo and 10.20% in Gambella. Seroprevalence and antibody levels against all 10 antigens were higher in Gambella than in Arjo. We observed spatial heterogeneities in seroprevalence across Arjo and smaller variations across Gambella. Seroprevalence in both sites was lowest against Pf CSP and highest against Pf AMA-1, Pf MSP-1 42 , and Pv MSPS-1 19 . Male sex, age, and agricultural occupation were positively associated with seropositivity in Arjo associations were less pronounced in Gambella. Our findings demonstrate that seroprevalence and antibody levels to specific Plasmodium antigens can be used to identify high-risk groups and geographical areas where interventions to reduce malaria transmission should be implemented.
Publisher: Elsevier BV
Date: 07-2022
DOI: 10.1016/J.STR.2022.03.018
Abstract: Plasmepsins IX (PMIX) and X (PMX) are essential aspartyl proteases for Plasmodium spp. egress, invasion, and development. WM4 and WM382 inhibit PMIX and PMX in Plasmodium falciparum and P. vivax. WM4 inhibits PMX, while WM382 is a dual inhibitor of PMIX and PMX. To understand their function, we identified protein substrates. Enzyme kinetic and structural analyses identified interactions responsible for drug specificity. PMIX and PMX have similar substrate specificity however, there are distinct differences for peptide and protein substrates. Differences in WM4 and WM382 binding for PMIX and PMX map to variations in the S' region and engagement of the active site S3 pocket. Structures of PMX reveal interactions and mechanistic detail of drug binding important for development of clinical candidates against these targets.
Publisher: Springer Science and Business Media LLC
Date: 06-2015
DOI: 10.1038/522158A
Publisher: Springer Science and Business Media LLC
Date: 28-04-2017
Publisher: Proceedings of the National Academy of Sciences
Date: 23-04-2021
Abstract: Neutralizing antibodies are important for immunity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and as therapeutics for the prevention and treatment of COVID-19. We identified high-affinity nanobodies against SARS-CoV-2 receptor-binding domain and found that nanobody cocktails consisting of two noncompeting nanobodies were able to block ACE2 engagement with RBD variants present in human populations and potently neutralize both wild-type SARS-CoV-2 and the N501Y D614G variant at low concentrations. Prophylactic administration of nanobody cocktails reduced viral loads in mice infected with the N501Y D614G SARS-CoV-2 virus, showing that nanobody cocktails are useful as prophylactic agents against SARS-CoV-2.
Publisher: Public Library of Science (PLoS)
Date: 22-12-2015
Publisher: Frontiers Media SA
Date: 28-07-2022
DOI: 10.3389/FIMMU.2022.889372
Abstract: Joining a function-enhanced Fc-portion of human IgG to the SARS-CoV-2 entry receptor ACE2 produces an antiviral decoy with strain transcending virus neutralizing activity. SARS-CoV-2 neutralization and Fc-effector functions of ACE2-Fc decoy proteins, formatted with or without the ACE2 collectrin domain, were optimized by Fc-modification. The different Fc-modifications resulted in distinct effects on neutralization and effector functions. H429Y, a point mutation outside the binding sites for FcγRs or complement caused non-covalent oligomerization of the ACE2-Fc decoy proteins, abrogated FcγR interaction and enhanced SARS-CoV-2 neutralization. Another Fc mutation, H429F did not improve virus neutralization but resulted in increased C5b-C9 fixation and transformed ACE2-Fc to a potent mediator of complement-dependent cytotoxicity (CDC) against SARS-CoV-2 spike (S) expressing cells. Furthermore, modification of the Fc-glycan enhanced cell activation via FcγRIIIa. These different immune profiles demonstrate the capacity of Fc-based agents to be engineered to optimize different mechanisms of protection for SARS-CoV-2 and potentially other viral pathogens.
Publisher: The American Association of Immunologists
Date: 02-2016
Abstract: The human complement system is the frontline defense mechanism against invading pathogens. The coexistence of humans and microbes throughout evolution has produced ingenious molecular mechanisms by which microorganisms escape complement attack. A common evasion strategy used by erse pathogens is the hijacking of soluble human complement regulators to their surfaces to afford protection from complement activation. One such host regulator is factor H (FH), which acts as a negative regulator of complement to protect host tissues from aberrant complement activation. In this report, we show that Plasmodium falciparum merozoites, the invasive form of the malaria parasites, actively recruit FH and its alternative spliced form FH-like protein 1 when exposed to human serum. We have mapped the binding site in FH that recognizes merozoites and identified Pf92, a member of the six-cysteine family of Plasmodium surface proteins, as its direct interaction partner. When bound to merozoites, FH retains cofactor activity, a key function that allows it to downregulate the alternative pathway of complement. In P. falciparum parasites that lack Pf92, we observed changes in the pattern of C3b cleavage that are consistent with decreased regulation of complement activation. These results also show that recruitment of FH affords P. falciparum merozoites protection from complement-mediated lysis. Our study provides new insights on mechanisms of immune evasion of malaria parasites and highlights the important function of surface coat proteins in the interplay between complement regulation and successful infection of the host.
Publisher: American Society of Tropical Medicine and Hygiene
Date: 05-2007
Publisher: Elsevier BV
Date: 02-2017
Publisher: Elsevier BV
Date: 06-2023
Publisher: Springer International Publishing
Date: 2018
Publisher: Research Square Platform LLC
Date: 07-10-2021
DOI: 10.21203/RS.3.RS-944781/V2
Abstract: Plasmepsin IX (PMIX) and X (PMX) are aspartyl proteases of Plasmodium spp. that play essential roles in parasite egress, invasion and development. Consequently, they are important drug targets for Plasmodium falciparum and P. vivax. WM4 and WM382 are potent inhibitors of PMIX and PMX that block invasion of liver and blood stages and transmission to mosquitoes. WM4 specifically inhibits PMX whilst WM382 is a dual inhibitor of PMIX and PMX. To understand the function of PMIX and PMX proteases we identified new protein substrates in P. falciparum and together with detailed kinetic analyses and structural analyses identified key molecular interactions in the active site responsible for the specificity of WM4 and WM382 inhibition. The crystal structures of PMX apo enzyme and the protease/drug complexes of PMX/WM382 and PMX/WM4 for P. falciparum and P. vivax have been solved. We show PMIX and PMX have similar substrate selectivity, however, there are distinct differences for both peptide and full-length protein substrates through differences in localised 3-dimensional structures for the enzyme substrate-binding cleft and substrate interface. The differences in affinities of WM4 and WM382 binding for PMIX and PMX map to variations in surface interactions with each protease in the S' region of the active sites. Crystal structures of PMX reveal interactions and mechanistic detail on the selectivity of drug binding which will be important for further development of clinical candidates against these important molecular targets.
Publisher: Public Library of Science (PLoS)
Date: 10-04-2012
Publisher: Elsevier BV
Date: 06-2022
Publisher: American Society for Clinical Investigation
Date: 23-08-2021
Publisher: American Society for Microbiology
Date: 03-2016
DOI: 10.1128/IAI.01117-15
Abstract: Members of the Plasmodium vivax reticulocyte binding protein (PvRBP) family are believed to mediate specific invasion of reticulocytes by P. vivax . In this study, we performed molecular characterization of genes encoding members of this protein family. Through cDNA sequencing, we constructed full-length gene models and verified genes that are protein coding and those that are pseudogenes. We also used quantitative PCR to measure their in vivo transcript abundances in clinical P. vivax isolates. Like genes encoding related invasion ligands of P. falciparum , Pvrbp expression levels vary broadly across different parasite isolates. Through antibody measurements, we found that host immune pressure may be the driving force behind the distinctly high ersity of one of the family members, PvRBP2c. Mild yet significant negative correlation was found between parasitemia and the PvRBP2b antibody level, suggesting that antibodies to the protein may interfere with invasion.
Publisher: Portland Press Ltd.
Date: 22-12-2022
DOI: 10.1042/BCJ20220554
Abstract: Transmission blocking interventions can stop malaria parasite transmission from mosquito to human by inhibiting parasite infection in mosquitos. One of the most advanced candidates for a malaria transmission blocking vaccine is Pfs230. Pfs230 is the largest member of the 6-cysteine protein family with 14 consecutive 6-cysteine domains and is expressed on the surface of gametocytes and gametes. Here, we present the crystal structure of the first two 6-cysteine domains of Pfs230. We identified high affinity Pfs230-specific nanobodies that recognized gametocytes and bind to distinct sites on Pfs230, which were isolated from immunized alpacas. Using two non-overlapping Pfs230 nanobodies, we show that these nanobodies significantly blocked P. falciparum transmission and reduced the formation of exflagellation centers. Crystal structures of the transmission blocking nanobodies with the first 6-cysteine domain of Pfs230 confirm that they bind to different epitopes. In addition, these nanobodies bind to Pfs230 in the absence of the prodomain, in contrast with the binding of known Pfs230 transmission blocking antibodies. These results provide additional structural insight into Pfs230 domains and elucidate a mechanism of action of transmission blocking Pfs230 nanobodies.
Publisher: American Society of Hematology
Date: 18-08-2011
DOI: 10.1182/BLOOD-2011-03-341305
Abstract: The Plasmodium falciparum adhesin PfRh4 binds to complement receptor type-1 (CR1) on human erythrocytes and mediates a glycophorin-independent invasion pathway. CR1 is a complement regulator and immune-adherence receptor on erythrocytes required for shuttling of C3b/C4b-opsonized particles to liver and spleen for phagocytosis. Using recombinant CR1 constructs, we mapped the recognition site for PfRh4 to complement control protein modules 1 to 3 (CCP1-3) at the membrane-distal amino terminus of CR1. This region of CR1 binds to C4b and C3b and accelerates decay of both classic pathway and alternative pathway C3 and C5 convertases. CCP1-3 competed for PfRh4 binding to erythroid CR1 and inhibited the PfRh4-CR1 invasion pathways across a wide range of P falciparum strains. PfRh4 did not bind significantly to other CR1 constructs, including CCP15-17, which is 85% identical to CCP1-3. PfRh4 binding to CR1 did not affect its C3b/C4b binding capability, and we show evidence for a ternary complex between CCP1-3, C4b, and PfRh4. PfRh4 binding specifically inhibited CR1's convertase decay-accelerating activity, whereas there was no effect on factor H-mediated decay-accelerating activity. These results increase our understanding of the functional implications of CR1 engagement with PfRh4 and highlight the interplay between complement regulation and infection.
Publisher: The American Association of Immunologists
Date: 15-06-2017
Abstract: The complement system is a front-line defense system that opsonizes and lyses invading pathogens. To survive, microbes exposed to serum must evade the complement response. To achieve this, many pathogens recruit soluble human complement regulators to their surfaces and hijack their regulatory function for protection from complement activation. C1 esterase inhibitor (C1-INH) is a soluble regulator of complement activation that negatively regulates the classical and lectin pathways of complement to protect human tissue from aberrant activation. In this article, we show that Plasmodium falciparum merozoites, the invasive form of blood stage malaria parasites, actively recruit C1-INH to their surfaces when exposed to human serum. We identified PfMSP3.1, a member of the merozoite surface protein 3 family of merozoite surface proteins, as the direct interaction partner. When bound to the merozoite surface, C1-INH retains its ability to complex with and inhibit C1s, MASP1, and MASP2, the activating proteases of the complement cascade. P. falciparum merozoites that lack PfMSP3.1 showed a marked reduction in C1-INH recruitment and increased C3b deposition on their surfaces. However, these ΔPfMSP3.1 merozoites exhibit enhanced invasion of RBCs in the presence of active complement. This study characterizes an immune-evasion strategy used by malaria parasites and highlights the complex relationship between merozoites and the complement system.
Publisher: Public Library of Science (PLoS)
Date: 23-11-2022
DOI: 10.1371/JOURNAL.PNTD.0010773
Abstract: To make progress towards malaria elimination, a highly effective vaccine targeting Plasmodium vivax is urgently needed. Evaluating the kinetics of natural antibody responses to vaccine candidate antigens after acute vivax malaria can inform the design of serological markers of exposure and vaccines. The responses of IgG antibodies to 9 P . vivax vaccine candidate antigens were evaluated in longitudinal serum s les from Brazilian in iduals collected at the time of acute vivax malaria and 30, 60, and 180 days afterwards. Antigen-specific IgG correlations, seroprevalence, and half-lives were determined for each antigen using the longitudinal data. Antibody reactivities against Pv41 and PVX_081550 strongly correlated with each other at each of the four time points. The analysis identified robust responses in terms of magnitude and seroprevalence against Pv41 and PvGAMA at 30 and 60 days. Among the 8 P . vivax antigens demonstrating % seropositivity across all in iduals, antibodies specific to PVX_081550 had the longest half-life (100 days 95% CI, 83–130 days), followed by PvRBP2b (91 days 95% CI, 76–110 days) and Pv12 (82 days 95% CI, 64–110 days). This study provides an in-depth assessment of the kinetics of antibody responses to key vaccine candidate antigens in Brazilians with acute vivax malaria. Follow-up studies are needed to determine whether the longer-lived antibody responses induced by natural infection are effective in controlling blood-stage infection and mediating clinical protection.
Publisher: Elsevier BV
Date: 04-2020
Publisher: Public Library of Science (PLoS)
Date: 19-08-2019
Publisher: American Association for the Advancement of Science (AAAS)
Date: 27-02-2004
Abstract: During meiosis, two chromosome segregation phases follow a single round of DNA replication. We identified factors required to establish this specialized cell cycle by examining meiotic chromosome segregation in a collection of yeast strains lacking all nonessential genes. This analysis revealed Sgo1, Chl4, and Iml3 to be important for retaining centromeric cohesin until the onset of anaphase II. Consistent with this role, Sgo1 localizes to centromeric regions but dissociates at the onset of anaphase II. The screen described here provides a comprehensive analysis of the genes required for the meiotic cell cycle and identifies three factors important for the stepwise loss of sister chromatid cohesion.
Publisher: American Society for Microbiology
Date: 06-2009
DOI: 10.1128/IAI.00048-09
Abstract: Plasmodium falciparum invasion into human erythrocytes relies on the interaction between multiple parasite ligands and their respective erythrocyte receptors. The sialic acid-independent invasion pathway is dependent on the expression of P. falciparum reticulocyte binding protein-like homologue 4 (PfRh4), as disruption of the gene abolishes the ability of parasites to switch to this pathway. We show that PfRh4 is present as an invasion ligand in culture supernatants as a 160-kDa proteolytic fragment. We confirm that PfRh4 binds to the surfaces of erythrocytes through recognition of an erythrocyte receptor that is neuraminidase resistant but trypsin and chymotrypsin sensitive. Serum antibodies from malaria-exposed in iduals show reactivity against the binding domain of PfRh4. Purified immunoglobulin G raised in rabbits against the binding domain of PfRh4 blocked the binding of native PfRh4 to the surfaces of erythrocytes and inhibited erythrocyte invasion of parasites using sialic acid-independent invasion pathways and grown in neuraminidase-treated erythrocytes. Our results suggest PfRh4 is a potential vaccine candidate.
Publisher: Cold Spring Harbor Laboratory
Date: 13-12-2020
DOI: 10.1101/2020.12.12.422521
Abstract: Surface-associated proteins play critical roles in the Plasmodium parasite life cycle and are major targets for vaccine development. The 6-cysteine (6-cys) protein family is expressed in a stage-specific manner throughout Plasmodium falciparum life cycle and characterized by the presence of 6-cys domains, which are β-sandwich domains with conserved sets of disulfide bonds. Although several 6-cys family members have been implicated to play a role in sexual stages, mosquito transmission, evasion of the host immune response and host cell invasion, the precise function of many family members is still unknown and structural information is only available for four 6-cys proteins. Here, we present to the best of our knowledge, the first crystal structure of the 6-cys protein Pf12p determined at 2.8 Å resolution. The monomeric molecule folds into two domains, D1 and D2, both of which adopt the canonical 6-cys domain fold. Although the structural fold is similar to that of Pf12, its paralog in P. falciparum , we show that Pf12p does not complex with Pf41, which is a known interaction partner of Pf12. We generated ten distinct Pf12p-specific nanobodies which map into two separate epitope groups one group which binds within the D2 domain, while several members of the second group bind at the interface of the D1 and D2 domain of Pf12p. Characterization of the structural features of the 6-cys family and their associated nanobodies provide a framework for generating new tools to study the erse functions of the 6-cys protein family in the Plasmodium life cycle.
Publisher: Cold Spring Harbor Laboratory
Date: 09-2022
DOI: 10.1101/2022.08.30.22279402
Abstract: To make progress towards malaria elimination, a highly effective vaccine targeting Plasmodium vivax is urgently needed. Evaluating the kinetics of natural antibody responses to vaccine candidate antigens after acute vivax malaria can inform the design of serological markers of exposure and vaccines. The responses of IgG antibodies to 9 P. vivax vaccine candidate antigens were evaluated in longitudinal serum s les from Brazilian in iduals collected at the time of acute vivax malaria and 30, 60, and 180 days afterwards. Antigen-specific IgG correlations, seroprevalence, and half-lives were determined for each antigen using the longitudinal data. Antibody reactivity against Pv41 and PVX_081550 strongly correlated within each of the four time points. The analysis identified robust responses in terms of magnitude and seroprevalence against Pv41 and PvGAMA at 30 and 60 days. Among the 8 P. vivax antigens demonstrating % seropositivity across all in iduals, antibodies specific to PVX_081550 had the longest half-life 100 days (95% CI, 83—130 days), followed by PvRBP2b (91 days 95% CI, 76—110 days) and Pv12 (82 days 95% CI, 64—110 days). This study provides an in-depth assessment of the kinetics of antibody responses to key vaccine candidate antigens in Brazilians with acute vivax malaria. Follow-up studies are needed to determine whether the longer-lived antibody responses induced by natural infection are effective in controlling blood-stage infection and mediating clinical protection. To successfully eliminate malaria, highly effective vaccines against the two major human malaria species, Plasmodium falciparum and Plasmodium vivax , will be needed. Vaccines against the blood form of malaria generate antibodies that target specific proteins on the Plasmodium parasite to reduce its replication within the host. Studying the antibody response after natural malaria infection can help identify blood markers of parasite exposure and also shed light on the magnitude and longevity of antibodies to vaccine candidate proteins. We performed a study to determine the frequency, magnitude, and longevity of natural antibody responses against nine P. vivax vaccine candidate proteins in patients with vivax malaria in Brazil. These proteins were selected based on prior studies demonstrating that antibodies against these proteins were either associated with protection against vivax malaria or have been tested as blood markers of recent infection with vivax malaria. We identify specific vivax proteins that produce more frequent and longer-lived antibody responses in this population.
Publisher: Elsevier BV
Date: 05-2007
Abstract: Subtelomeric regions in the Plasmodium genome are enriched with members of three major multigene families: var, rif and stevor. In this article, we discuss a recent study by Sharp and colleagues that focused on the transcribed repertoire of var and stevor genes in asexual and sexual Plasmodium parasites. Transcription of these two multigene families seems to be unlinked in asexual parasites. Parasites in the gametocyte stages transcribe members of the upsC subset of var genes, which indicates the intriguing possibility of their involvement in gametocyte adhesion.
Publisher: Proceedings of the National Academy of Sciences
Date: 20-08-2018
Abstract: Chimpanzees, bonobos, and gorillas harbor close relatives of human Plasmodium vivax , but current knowledge of these parasites is limited to a small number of gene fragments derived almost exclusively from mitochondrial DNA. We compared nearly full-length genomes of ape parasites with a global s le of human P. vivax and tested the function of human and ape P. vivax proteins believed to be important for erythrocyte binding. The results showed that ape parasites are 10-fold more erse than human P. vivax and exhibit no evidence of species specificity, whereas human P. vivax represents a bottlenecked lineage that emerged from within this parasite group. Thus, African apes represent a large P. vivax reservoir whose impact on human malaria eradication requires careful monitoring.
Publisher: Elsevier BV
Date: 07-2016
DOI: 10.1016/J.CHOM.2016.06.004
Abstract: Plasmodium falciparum parasites in the merozoite stage invade human erythrocytes and cause malaria. Invasion requires multiple interactions between merozoite ligands and erythrocyte receptors. P. falciparum reticulocyte binding homolog 5 (PfRh5) forms a complex with the PfRh5-interacting protein (PfRipr) and Cysteine-rich protective antigen (CyRPA) and binds erythrocytes via the host receptor basigin. However, the specific role that PfRipr and CyRPA play during invasion is unclear. Using P. falciparum lines conditionally expressing PfRipr and CyRPA, we show that loss of PfRipr or CyRPA function blocks growth due to the inability of merozoites to invade erythrocytes. Super-resolution microscopy revealed that PfRipr, CyRPA, and PfRh5 colocalize at the junction between merozoites and erythrocytes during invasion. PfRipr, CyRPA, and PfRipr/CyRPA/PfRh5-basigin complex is required for triggering the Ca(2+) release and establishing the tight junction. Together, these results establish that the PfRh5/PfRipr/CyRPA complex is essential in the sequential molecular events leading to parasite invasion of human erythrocytes.
Publisher: Elsevier BV
Date: 2022
Publisher: American Society for Microbiology
Date: 03-2011
DOI: 10.1128/IAI.01021-10
Abstract: Plasmodium falciparum causes the most severe form of malaria in humans and invades erythrocytes using multiple ligand-receptor interactions. Two important protein families involved in erythrocyte binding are the erythrocyte binding-like (EBL) and the reticulocyte binding-like (RBL or P. falciparum Rh [PfRh]) proteins. We constructed P. falciparum lines lacking expression of EBL proteins by creating single and double knockouts of the corresponding genes for eba-175 , eba-181 , and eba-140 and show that the EBL and PfRh proteins function cooperatively, consistent with them playing a similar role in merozoite invasion. We provide evidence that PfRh and EBL proteins functionally interact, as loss of function of EBA-181 ablates the ability of PfRh2a/b protein antibodies to inhibit merozoite invasion. Additionally, loss of function of some ebl genes results in selection for increased transcription of the PfRh family. This provides a rational basis for considering PfRh and EBL proteins for use as a combination vaccine against P. falciparum . We immunized rabbits with combinations of PfRh and EBL proteins to test the ability of antibodies to block merozoite invasion in growth inhibition assays. A combination of EBA-175, PfRh2a/b, and PfRh4 recombinant proteins induced antibodies that potently blocked merozoite invasion. This validates the use of a combination of these ligands as a potential vaccine that would have broad activity against P. falciparum .
Publisher: Cold Spring Harbor Laboratory
Date: 13-05-2020
DOI: 10.1101/2020.05.12.091900
Abstract: Plasmodium vivax preferentially invades reticulocytes and recognition of these cells is mediated by P. vivax Reticulocyte Binding Protein 2b (PvRBP2b) binding to human Transferrin receptor 1 (TfR1) and Transferrin (Tf). Longitudinal cohort studies in Papua New Guinea, Thailand and Brazil show that PvRBP2b antibodies are correlated with protection against P. vivax infection and disease. Here, we isolated and characterized anti-PvRBP2b human monoclonal antibodies from two in iduals in Cambodia with natural P. vivax infection. These antibodies bind with high affinities and map to different regions of PvRBP2b. Several human antibodies blocked PvRBP2b binding to reticulocytes and inhibited complex formation with human TfR1-Tf. We describe different structural mechanisms for functional inhibition, including either steric hindrance with TfR1-Tf or the reticulocyte membrane. These results show that naturally acquired human antibodies against PvRBP2b can inhibit its function which is important for P. vivax invasion.
Publisher: Public Library of Science (PLoS)
Date: 15-02-2019
Publisher: Frontiers Media SA
Date: 08-07-2022
DOI: 10.3389/FCIMB.2022.945924
Abstract: The 6-cysteine protein family is one of the most abundant surface antigens that are expressed throughout the Plasmodium falciparum life cycle. Many members of the 6-cysteine family have critical roles in parasite development across the life cycle in parasite transmission, evasion of the host immune response and host cell invasion. The common feature of the family is the 6-cysteine domain, also referred to as s48/45 domain, which is conserved across Aconoidasida. This review summarizes the current approaches for recombinant expression for 6-cysteine proteins, monoclonal antibodies against 6-cysteine proteins that block transmission and the growing collection of crystal structures that provide insights into the functional domains of this protein family.
Publisher: Public Library of Science (PLoS)
Date: 27-09-2016
Publisher: Springer Science and Business Media LLC
Date: 09-03-2021
DOI: 10.1038/S41467-021-21811-2
Abstract: Plasmodium vivax preferentially invades reticulocytes and recognition of these cells is mediated by P. vivax Reticulocyte Binding Protein 2b (PvRBP2b) binding to human Transferrin receptor 1 (TfR1) and Transferrin (Tf). Longitudinal cohort studies in Papua New Guinea, Thailand and Brazil show that PvRBP2b antibodies are correlated with protection against P. vivax infection and disease. Here, we isolate and characterize anti-PvRBP2b human monoclonal antibodies from two in iduals in Cambodia with natural P. vivax infection. These antibodies bind with high affinities and map to different regions of PvRBP2b. Several human antibodies block PvRBP2b binding to reticulocytes and inhibit complex formation with human TfR1-Tf. We describe different structural mechanisms for functional inhibition, including either steric hindrance with TfR1-Tf or the reticulocyte membrane. These results show that naturally acquired human antibodies against PvRBP2b can inhibit its function which is important for P. vivax invasion.
Publisher: Wiley
Date: 2022
DOI: 10.1002/CTI2.1424
Abstract: Following infection with SARS‐CoV‐2, virus‐specific antibodies are generated, which can both neutralise virions and clear infection via Fc effector functions. The importance of IgG antibodies for protection and control of SARS‐CoV‐2 has been extensively reported. By comparison, other antibody isotypes including IgA have been poorly characterised. Here, we characterised plasma IgA from 41 early convalescent COVID‐19 subjects for neutralisation and Fc effector functions. Convalescent plasma IgA from 60% of the cohort had the capacity to inhibit the interaction between wild‐type RBD and ACE2. Furthermore, a third of the cohort induced stronger IgA‐mediated ACE2 inhibition than matched IgG when tested at equivalent concentrations. Plasma IgA and IgG from this cohort broadly recognised similar RBD epitopes and had similar capacities to inhibit ACE2 from binding to 22 of the 23 prevalent RBD mutations assessed. However, plasma IgA was largely incapable of mediating antibody‐dependent phagocytosis in comparison with plasma IgG. Overall, convalescent plasma IgA contributed to the neutralising antibody response of wild‐type SARS‐CoV‐2 RBD and various RBD mutations. However, this response displayed large heterogeneity and was less potent than IgG.
Publisher: Springer Science and Business Media LLC
Date: 05-2020
Publisher: Springer Science and Business Media LLC
Date: 2000
DOI: 10.1038/47385
Publisher: Elsevier BV
Date: 09-2009
Publisher: Proceedings of the National Academy of Sciences
Date: 29-12-2016
Abstract: Plasmodium vivax is responsible for the most widely distributed recurring human malaria infections whereas Plasmodium falciparum inflicts the most mortality and morbidity in human populations. Malaria parasites enter our blood cells by making proteins that recognize and bind to their cognate receptors on the red blood cell surface. Our research describes, to our knowledge, the first crystal structure of PvRBP2a, an erythrocyte-binding protein from P. vivax, which revealed a structural scaffold similar to that of PfRh5, the essential erythrocyte-binding protein in P. falciparum . Structural comparisons between PvRBP2a and PfRh5 provide an important foundation toward understanding how P. vivax and P. falciparum parasites use a homologous erythrocyte-binding protein family to engage alternate erythrocyte receptors and ultimately govern host cell specificity.
Publisher: Hindawi Limited
Date: 11-2009
Publisher: Elsevier BV
Date: 10-2021
Publisher: Springer Science and Business Media LLC
Date: 17-11-2022
DOI: 10.1038/S41564-022-01261-2
Abstract: The most severe form of malaria is caused by Plasmodium falciparum . These parasites invade human erythrocytes, and an essential step in this process involves the ligand PfRh5, which forms a complex with cysteine-rich protective antigen (CyRPA) and PfRh5-interacting protein (PfRipr) (RCR complex) and binds basigin on the host cell. We identified a heteromeric disulfide-linked complex consisting of P. falciparum Plasmodium thrombospondin-related apical merozoite protein (PfPTRAMP) and P. falciparum cysteine-rich small secreted protein (PfCSS) and have shown that it binds RCR to form a pentameric complex, PCRCR. Using P. falciparum lines with conditional knockouts, invasion inhibitory nanobodies to both PfPTRAMP and PfCSS, and lattice light-sheet microscopy, we show that they are essential for merozoite invasion. The PCRCR complex functions to anchor the contact between merozoite and erythrocyte membranes brought together by strong parasite deformations. We solved the structure of nanobody–PfCSS complexes to identify an inhibitory epitope. Our results define the function of the PCRCR complex and identify invasion neutralizing epitopes providing a roadmap for structure-guided development of these proteins for a blood stage malaria vaccine.
Publisher: Portland Press Ltd.
Date: 10-02-2021
DOI: 10.1042/BCJ20200415
Abstract: Surface-associated proteins play critical roles in the Plasmodium parasite life cycle and are major targets for vaccine development. The 6-cysteine (6-cys) protein family is expressed in a stage-specific manner throughout Plasmodium falciparum life cycle and characterized by the presence of 6-cys domains, which are β-sandwich domains with conserved sets of disulfide bonds. Although several 6-cys family members have been implicated to play a role in sexual stages, mosquito transmission, evasion of the host immune response and host cell invasion, the precise function of many family members is still unknown and structural information is only available for four 6-cys proteins. Here, we present to the best of our knowledge, the first crystal structure of the 6-cys protein Pf12p determined at 2.8 Å resolution. The monomeric molecule folds into two domains, D1 and D2, both of which adopt the canonical 6-cys domain fold. Although the structural fold is similar to that of Pf12, its paralog in P. falciparum, we show that Pf12p does not complex with Pf41, which is a known interaction partner of Pf12. We generated 10 distinct Pf12p-specific nanobodies which map into two separate epitope groups one group which binds within the D2 domain, while several members of the second group bind at the interface of the D1 and D2 domain of Pf12p. Characterization of the structural features of the 6-cys family and their associated nanobodies provide a framework for generating new tools to study the erse functions of the 6-cys protein family in the Plasmodium life cycle.
Location: Australia
Start Date: 2017
End Date: 2022
Funder: Wellcome Trust
View Funded ActivityStart Date: 2016
End Date: 2020
Funder: National Health and Medical Research Council
View Funded ActivityStart Date: 2013
End Date: 12-2016
Amount: $706,528.00
Funder: Australian Research Council
View Funded ActivityStart Date: 09-2006
End Date: 07-2008
Amount: $330,000.00
Funder: Australian Research Council
View Funded Activity