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    Molecular recognition of the native HIV-1 MPER revealed by STED microscopy of single virions
    (Berlin : Nature Publishing, 2019) Carravilla, Pablo; Chojnacki, Jakub; Rujas, Edurne; Insausti, Sara; Largo, Eneko; Waithe, Dominic; Apellaniz, Beatriz; Sicard, Taylor; Julien, Jean-Philippe; Eggeling, Christian; Nieva, José L.
    Antibodies against the Membrane-Proximal External Region (MPER) of the Env gp41 subunit neutralize HIV-1 with exceptional breadth and potency. Due to the lack of knowledge on the MPER native structure and accessibility, different and exclusive models have been proposed for the molecular mechanism of MPER recognition by broadly neutralizing antibodies. Here, accessibility of antibodies to the native Env MPER on single virions has been addressed through STED microscopy. STED imaging of fluorescently labeled Fabs reveals a common pattern of native Env recognition for HIV-1 antibodies targeting MPER or the surface subunit gp120. In the case of anti-MPER antibodies, the process evolves with extra contribution of interactions with the viral lipid membrane to binding specificity. Our data provide biophysical insights into the recognition of the potent and broadly neutralizing MPER epitope on HIV virions, and as such is of importance for the design of therapeutic interventions.
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    Mechanical properties of plasma membrane vesicles correlate with lipid order, viscosity and cell density
    (Berlin : Nature Publishing, 2019) Steinkühler, Jan; Sezgin, Erdinc; Urbančič, Iztok; Eggeling, Christian; Dimova, Rumiana
    Regulation of plasma membrane curvature and composition governs essential cellular processes. The material property of bending rigidity describes the energetic cost of membrane deformations and depends on the plasma membrane molecular composition. Because of compositional fluctuations and active processes, it is challenging to measure it in intact cells. Here, we study the plasma membrane using giant plasma membrane vesicles (GPMVs), which largely preserve the plasma membrane lipidome and proteome. We show that the bending rigidity of plasma membranes under varied conditions is correlated to readout from environment-sensitive dyes, which are indicative of membrane order and microviscosity. This correlation holds across different cell lines, upon cholesterol depletion or enrichment of the plasma membrane, and variations in cell density. Thus, polarity- and viscosity-sensitive probes represent a promising indicator of membrane mechanical properties. Additionally, our results allow for identifying synthetic membranes with a few well defined lipids as optimal plasma membrane mimetics.