ORCID Profile
0000-0002-6023-1519
Current Organisation
RMIT University
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Publisher: Elsevier BV
Date: 12-2017
DOI: 10.1016/J.COLSURFB.2017.10.006
Abstract: Chaplin E, or Chp E, is a surface active peptide secreted by Streptomyces coelicolor that adopts different structures depending on solution pH but the effect of these structures on the interfacial properties of Chp E is not known. In experiments paired with simulations, Chp E was found to display pH-dependent interfacial assembly and surface activity. At pH 3.0, Chp E formed an ordered non-amyloidal interfacial film with high surface activity while at pH 10.0, Chp E self-assembled into a heterogeneous film containing randomly arranged fibrils at the interface that was less surface active compared to the film formed at pH 3.0. In simulations at pH 10.0, Chp E molecules showed a higher propensity for dimerization within the solution phase, lower rate of adsorption to the interface and tighter inter-molecular associations at the interface, consistent with the lower surface activity and smaller interfacial area coverage per molecule measured at this pH compared to at pH 3.0. A model is presented for the role of Chp E in the developmental differentiation of Streptomyces coelicolor, where Chp E contributes to changes in surface tension at low pH and the formation of fibrils on the surface of aerial hyphae at high pH. Our data also suggest Chp E could be a promising surface active agent with functional activity that can be controlled by pH.
Publisher: Elsevier BV
Date: 07-2020
Publisher: Springer Science and Business Media LLC
Date: 10-01-2022
DOI: 10.1007/S11483-021-09713-8
Abstract: There is an increasing demand for the design of complex bio-composites with customized structural characteristics for use in processed food products. Phase behaviour of these mixtures determines textural properties, encouraging the pursue of a rapid technique that can accurately quantify it. The present work tests the efficacy of confocal laser scanning microscopy (CLSM) coupled with image analysis software (Imaris), for the quantification of phase behaviour in complex tertiary systems. In doing so, it develops phase separated gels of agarose and gelatin supporting inclusions of canola oil. The polysaccharide was replaced with whey protein isolate (WPI) and the topology of the tertiary dispersion with gelatin and canola oil was also examined. Reproducible phase volume estimates were obtained, including those of the lipid phase, which were a close match to the actual concentrations added to the hydrocolloid gel. The approach could offer an alternative to the rheological estimation, via theoretical blending law analysis, of phase volumes in bio-composites. Graphical Abstract
Publisher: Elsevier BV
Date: 2010
Publisher: Elsevier BV
Date: 02-2020
DOI: 10.1016/J.IJBIOMAC.2019.12.075
Abstract: The Chaplin E peptide is a surface-active agent that can adsorb to the air/water interface and form interfacial films that display distinct interfacial properties as a function of pH. The ~2 nm thick homogeneous Chaplin E film formed under acidic conditions contains ordered structures that give a high dilatational elasticity. In contrast, the heterogeneous film formed under basic conditions contained fibrils resulting in a rough ~17 nm thick film with predominantly viscoelastic properties, probably due to the reduced intermolecular interactions. These fibrils were also susceptible to breakage, fragmenting into shorter fibrils, which gave a greater elasticity. The fibrils also lead to a greater shear viscosity compared to the ordered structures aligned within the Chaplin E film at pH 3.0. A higher stability was observed for the foam formed by the Chaplin E compared to the foam formed by β-lactoglobulin, consistent with the greater rheological properties observed for the Chaplin E film at the interface. Our findings suggest that Chaplin E has potential to provide long time stability to dispersions in food, consumer goods or pharmaceutical applications, forming films with greater rheological properties and at least similar thickness to those formed by other surface-active proteins such as β-casein and β-lactoglobulin.
Publisher: Elsevier BV
Date: 05-2017
DOI: 10.1016/J.JSB.2017.04.004
Abstract: Chaplin E, is one of five self-assembling peptides secreted by Streptomyces coelicolor that assist aerial growth by lowering the surface tension of water. Although the surface activity of a mixture of chaplin peptides has observed to depend on pH, it is unclear how the solvent environment (i.e. pH) influences the structure, assembly and subsequent functionality of these in idual peptides. In this study, the conformation and fibril forming propensity of the Chaplin E peptide was assessed as a function of pH using a combination of experimental measurements and molecular dynamics simulations. At an acidic pH of 3.0, Chaplin E retained a random coil structure, whereas at the isoelectric point of 6.7 or a basic pH of 10.0, Chaplin E rapidly formed amyloid fibrils rich in β-sheet structure with high efficiency (>93%). Molecular dynamics simulations indicate the persistence of greater α-helical content at the N-terminus at high pH this is likely partly due to the lack of electrostatic repulsion between residues His6 and Lys10. Since fibril formation was observed at high but not at low pH, we propose that the presence of an N-terminal α-helix in the monomeric form of Chaplin E is required for aggregation and conversion to β-amyloid fibrils. The pH sensitivity of Chaplin E peptide structure provides a route to control peptide assembly and may be important for the physiological function of this peptide, as a surface active agent in the transition from vegetative to aerial growth and could assist Streptomyces coelicolor in response to environmental fluctuations in pH.
Publisher: Elsevier BV
Date: 04-2022
Publisher: MDPI AG
Date: 19-09-2017
DOI: 10.3390/BIOM7030068
Publisher: Elsevier BV
Date: 05-2021
Publisher: Elsevier BV
Date: 11-2019
DOI: 10.1016/J.FOODRES.2019.108529
Abstract: Studying the phase behaviour of composite gels facilitates understanding of their structural and textural properties at low and intermediate levels of solids. In this work, the phase behaviour of a model system of agarose including various concentrations of canola oil was studied. This was pursued using a variety of techniques including SEM, FTIR, microDSC and dynamic oscillation in-shear. The structural studies recorded strong, continuous agarose networks supporting soft, discontinuous canola oil inclusions, with increasing levels of canola oil strengthening the composite system. A novel confocal laser scanning microscopy (CLSM) method for quantitative in situ examination of the oil phase volume was developed using three-dimensional (3D) imaging and image analysis software - FIJI and Imaris. Microscopic observations were assessed in relation to theoretical predictions from rheology-based blending-law analysis. Quantitative outcomes from the combined 3D imaging and image analysis are in close agreement with the volume predictions for the oil phase obtained from the isostrain blending law indicating the suitability of this approach in quantifying the phase behaviour of composite materials. The results of this work indicate that the developed microscopic method shows promise and could be used in the determination of phase volume in more complex and industrially relevant systems.
No related grants have been discovered for Mina Dokouhaki.