ORCID Profile
0000-0003-0118-2443
Current Organisations
University of Tokyo
,
Le Verre Fluoré
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Publisher: Cold Spring Harbor Laboratory
Date: 15-08-2021
DOI: 10.1101/2021.08.15.456392
Abstract: ChRmine 1 , a recently-discovered bacteriorhodopsin-like cation-conducting channelrhodopsin 1, 2 , exhibits puzzling properties (unusually-large photocurrents, exceptional red-shift in action spectrum, and extreme light-sensitivity) that have opened up new opportunities in optogenetics 1, 3–5 . ChRmine and its homologs function as light-gated ion channels, but by primary sequence more closely resemble ion pump rhodopsins the molecular mechanisms for passive channel conduction in this family of proteins, as well as the unusual properties of ChRmine itself, have remained mysterious. Here we present the cryo-electron microscopy structure of ChRmine at 2.0 Å resolution. The structure reveals striking architectural features never seen before in channelrhodopsins including trimeric assembly, a short transmembrane-helix 3 unwound in the middle of the membrane, a prominently-twisting extracellular-loop 1, remarkably-large intracellular cavities and extracellular vestibule, and an unprecedented hydrophilic pore that extends through the center of the trimer, separate from the three in idual monomer pores. Electrophysiological, spectroscopic, and computational analyses provide insight into conduction and gating of light-gated channels with these distinct design features, and point the way toward structure-guided creation of novel channelrhodopsins for optogenetic applications in biology.
Publisher: Optica Publishing Group
Date: 27-06-2023
DOI: 10.1364/OME.493834
Abstract: We demonstrate a new design for active fluoride glass fibres in which a metal coating instead of a polymer coating is applied. A 2- μ m-thick silver layer is fabricated chemically to the periphery of the fiber, that in this case is doped with Dy 3+ ions, and coating lengths of up to 20 cm were produced. The temperature rise in the core of the fiber was accurately measured using a sensitive fiber Mach-Zenhder interferometer (MZI) employing a stabilised He-Ne laser. We use this setup to show that the metal coating can achieve a reduction in the fibre core temperature by up to 22% for low launched pump power levels. A basic two-dimensional model shows reasonable agreement with the experiment. This work paves the way for the development of active fluoride fiber applications in which reducing and stabilising the temperature of the fibre is critical.
Publisher: Elsevier BV
Date: 2019
Publisher: Springer Science and Business Media LLC
Date: 13-10-2015
DOI: 10.1038/NCOMMS9545
Abstract: In vertebrates, the iron exporter ferroportin releases Fe 2+ from cells into plasma, thereby maintaining iron homeostasis. The transport activity of ferroportin is suppressed by the peptide hormone hepcidin, which exhibits upregulated expression in chronic inflammation, causing iron-restrictive anaemia. However, due to the lack of structural information about ferroportin, the mechanisms of its iron transport and hepcidin-mediated regulation remain largely elusive. Here we report the crystal structures of a putative bacterial homologue of ferroportin, BbFPN, in both the outward- and inward-facing states. Despite undetectable sequence similarity, BbFPN adopts the major facilitator superfamily fold. A comparison of the two structures reveals that BbFPN undergoes an intra-domain conformational rearrangement during the transport cycle. We identify a substrate metal-binding site, based on structural and mutational analyses. Furthermore, the BbFPN structures suggest that a predicted hepcidin-binding site of ferroportin is located within its central cavity. Thus, BbFPN may be a valuable structural model for iron homeostasis regulation by ferroportin.
Publisher: Cold Spring Harbor Laboratory
Date: 31-10-2022
DOI: 10.1101/2022.10.30.514430
Abstract: The KCR channelrhodopsins are recently-discovered light-gated ion channels with high K + selectivity, a property that has attracted broad attention among biologists– due to intense interest in creating novel inhibitory tools for optogenetics leveraging this K + selectivity, and due to the mystery of how this selectivity is achieved in the first place. Indeed, the molecular and structural mechanism for K + selectivity in KCRs has remained especially puzzling since these 7-transmembrane retinal-binding proteins completely lack structural similarity with known K + channels, which generally coordinate K + in a precisely symmetric conduction pathway formed by a tight interface among multiple small monomeric channel subunits (presumably not an accessible mechanism for the large KCR rhodopsin proteins). Here we present the cryo-electron microscopy structures of two KCRs from Hyphochytrium catenoides with distinct spectral properties for light absorption and channel actuation, Hc KCR1, and Hc KCR2, at resolutions of 2.6 and 2.5 Å, respectively. Structural comparison revealed first an unusually-shaped retinal binding pocket which induces rotation of the retinal in Hc KCR2, explaining the large spectral difference between Hc KCR1 and 2. Next, our combined structural, electrophysiological, computational, and spectroscopic analyses revealed a new solution to the challenging problem of K + -selective transport. KCRs indeed do not exhibit the canonical tetrameric K + selectivity filter that specifically coordinates dehydrated K + instead, single KCR monomers form a size exclusion filter using aromatic residues at the extracellular side of the pore which inhibits passage of bulky hydrated ions. This unique feature allows KCRs to function as K + channels under relevant physiological conditions, providing not only a novel mechanism for achieving high K + permeability ratios in biological ion channels, but also a framework for designing the next generation of inhibitory optogenetic tools. The first structures of K + -selective channelrhodopsins ( Hc KCR1 and 2) are determined, revealing a K + selectivity mechanism distinctly different from canonical K + channels. The cryo-EM structures of K + -selective channelrhodopsins, Hc KCR1 and 2, in nanodisc Conditions under which naturally-occurring microbial rhodopsins have a 6-s- cis retinal Identification of key residues for high K + permeability ratios The unique K + selectivity mechanism of KCRs
Publisher: Elsevier BV
Date: 02-2022
Publisher: Springer Science and Business Media LLC
Date: 29-08-2022
DOI: 10.1038/S41598-022-18701-Y
Abstract: Zirconium fluoride (ZBLAN) glass, the standard material used in fiber-based mid-infrared photonics, has been re-designed to enable the fabrication of high index-contrast low-loss waveguides via femtosecond laser direct writing. We demonstrate that in contrast to pure ZBLAN, a positive index change of close to 10 −2 can be induced in hybrid zirconium/hafnium (Z/HBLAN) glasses during ultrafast laser inscription and show that this can be explained by an electron cloud distortion effect that is driven by the existence of two glass formers with contrasting polarizability. High numerical aperture (NA) type-I waveguides that support a well confined 3.1 μm wavelength mode with a mode-field diameter (MFD) as small as 12 μm have successfully been fabricated. These findings open the door for the fabrication of mid-infrared integrated photonic devices that can readily be pigtailed to existing ZBLAN fibers.
No related grants have been discovered for Solenn Cozic.