Biophysical Society Conference | Tahoe 2022

Molecular Biophysics of Membranes

Poster Abstracts

7-POS Board 2 CHOLESTEROL DISTRIBUTIONS AND INTERACTIONS IN EARLY FUSION PORES Andrew H Beaven 1,2 ; Kayla C Sapp 1 ; Jefferson D Knight 3 ; Alexander J Sodt 1 ;

1 NIH, NICHD, Bethesda, MD, USA 2 NIH, NIGMS, Bethesda, MD, USA 3 University of Colorado Denver, Chemistry, Denver, CO, USA

We have used all-atom molecular dynamics (MD) simulations to study cholesterol’s preferred distributions in early lipid-only fusion pores. These MD simulations demonstrate that cholesterol is excluded from early fusion pores that have strong negative curvature (i.e., lipids bend toward their head groups). Previous experimental and computational data have demonstrated that cholesterol has a strong negative curvature preference, so why is cholesterol excluded from this region? Guided by complementary evidence, we propose that cholesterol is excluded from the pore for two interrelated reasons. (1) Gaussian (saddle) curvature thins the pore’s bilayer interior (i.e., the region between the two leaflets’ neutral surfaces) and cholesterol prefers thicker bilayers. (2) Cholesterol has a strong Gaussian modulus that is incompatible with this pore’s saddle curvature. By adding saddle curvature considerations into a theoretical model, we produce predicted lipid distributions in good agreement with simulation. Recent work from the Francis lab at Univ. South Dakota has demonstrated that sterols lower the energetic barriers for clathrin- mediated endocytosis (Anderson et al. Cell Reports. 2021.). Therefore, cholesterol redistribution at early steps of fusion could shift a pore’s geometry and be a critical part of endocytosis. We also detail an imperative fusion protein, synaptotagmin 7 (Syt7). We demonstrate that Syt7’s tandem domains (C2A and C2B) induce drastically different membrane curvature. We then show that these domains sequester anionic lipids (e.g., PIP 2 and POPS) and cholesterol. We use geometric and physical modeling to show why cholesterol is sequestered. We posit that these sequestrations will affect the local lipid populations, thereby influencing fusion pore opening/closure.

81