Biophysical Society Conference | Estes Park 2023

Membrane Budding and Fusion

Poster Abstracts

18-POS Board 6 HOW DO THE CHEMICAL PROPERTIES OF PROTEINS INDUCE AND STABILIZE MEMBRANE CURVATURE? Frank R Moss 1,4 ; James Lincoff 2,3 ; Arshad Mohammed 1,4 ; Maxwell Tucker 2,3 ; Michael Grabe 2,3 ; Adam Frost 1,4,5 ; 1 University of California- San Francisco, Biochemistry and Biophysics, San Francisco, CA, USA 2 University of California- San Francisco, Pharmaceutical Chemistry, San Francisco, CA, USA 3 University of California- San Francisco, Cardiovascular Research Institute, San Francisco, CA, USA 4 Altos Labs, Bay Area Institute, Redwood City, CA, USA 5 Chan Zuckerberg Biohub, San Francisco, CA, USA The remodeling of biological membranes is an essential process that maintains their necessary shapes, sizes, compositions, and connectivity. Despite the importance of membrane remodeling, many aspects of membrane fusion and fission remain poorly understood, including how proteins assemble on membranes and convert chemical energy into mechanical forces needed to deform membranes. We utilize a combination of chemical synthesis, biophysics, cryo-electron microscopy (cryo-EM), and molecular dynamics (MD) simulations to investigate how one class of fission proteins (ESCRT-III) remodels membranes and alters the physical properties of lipid bilayers to lower the energy barrier for membrane fission. To study the nanoscale structure of highly constricted bilayers, we have generated cryo-EM reconstructions of ESCRT-III-bound membranes with brominated analogs of lipids, which strongly scatter electrons, to reveal lipid leaflet asymmetry induced by high curvature and molecular details of lipid packing. Due to curvature stress from membrane constriction, lipids with negative spontaneous curvature are enriched in the inner leaflet, and lipids with positive spontaneous curvature are enriched in the outer leaflet. Additionally, the ESCRT-III proteins highly distort the structure of the bilayer by substantial thinning of the concave leaflet and displacing lipid headgroups at protein-membrane contact sites. Next, we generated an array of mutants to systematically vary the charge, size, hydrophobicity, and aromaticity of the residues proximal to the bilayer to investigate how the chemical environment created by the proteins around the lipid bilayer generates and stabilizes curvature. Finally, we investigated the role of lipid structure in remodeling by systematically varying lipid composition and observing the change in the energy needed to remodel vesicles into nanotubes. Together, these data provide insight into how ESCRT-III proteins can alter membrane structure to overcome the energetic barrier to curvature generation and ultimately fission.

99