Biophysical Society Conference | Tahoe 2022

Molecular Biophysics of Membranes

Poster Abstracts

12-POS Board 3 AN INVESTIGATION OF HOW LIPID PACKING IMPACTS SEPTIN ASSOCIATION AND ASSEMBLY Brandy Curtis 1,2 ; Christopher Edelmaier 3 ; Amy Gladfelter 1 ; 1 University of North Carolina-Chapel Hill, Biology, Chapel Hill, NC, USA 2 University of North Carolina-Chapel Hill, Biochemistry and Biophysics, Chapel Hill, NC, USA 3 University of North Carolina-Chapel Hill, Applied Physical Science, Chapel Hill, NC, USA Throughout the lifecycle of most cells, they must be able to sense, generate, and react to changes in their shape. Cell shape can be described in terms of membrane curvature which may span nanometer to micrometer length scales. While nanometer-scale curvature sensors are well- documented in processes such as in endocytosis and cell trafficking, there are few known sensors of micrometer-scale curvature. Septins are filament-forming proteins necessary for cell processes involving major changes to cell shape, such as cytokinesis and polarized growth, and are intrinsically sensitive to micrometer-scale membrane curvature. Interestingly, they possess an amphipathic helix (AH) that is necessary and sufficient for septin curvature sensitivity but is structurally similar to AH domains specific to nanometer-scale curvature. How do these small helical domains give rise to micrometer curvature sensitivity? Previous work has shown that changes to lipid composition that alter lipid packing may mimic membrane curvature, and this may be especially relevant for septins which are capable of localizing to many different geometries, both in vitro and in vivo. This work focuses on revealing the impact of lipid packing on septin association and assembly by changing the physicochemical properties of the membrane that may help septins “sense” curvature, such as the identity of the head group and the degree of lipid packing. Using a combination of molecular dynamics simulations and the membrane tension dye, FLIPT-R, we have assembled lipid compositions that span from loosely packed to tightly packed. We measure septin association rates and observe septin assembly over time on these different compositions using in vitro reconstitution assays on supported lipid bilayers to assess how modulating membrane properties may alter septin assembly independently of curvature. As lipid packing becomes tighter, septin association and assembly rates decrease, signifying both membrane geometry and lipid packing may be regulating spatio-specific localization of septins.

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