Cellular transport processes such as endocytosis and exocytosis involve the budding of vesicles from the donor membrane (fission) and their integration into the membrane of the acceptor compartment (fusion). Both fission and fusion are energetically unfavorable, since they involve the formation of highly curved non-bilayer intermediates. Consequently, these processes do not occur spontaneously— they are under the strict control of specific proteins.

In the classical paradigm of fission, membrane deformation was thought to be driven entirely by interactions between proteins. Evidence is now accumulating that these proteins do not act alone. They operate in concert with specific membrane lipids, such as phosphoinositides (PI), which localize in the region of deformation. It is of interest to understand the extent to which the localized phosphoinositides change the mechanical properties of biomembranes.

In this talk, we will begin by presenting the analysis of coarse-grained molecular dynamics (MD) simulations, which show the effect of the lipid composition on two elastic parameters of the membrane, namely, the bending modulus and the coefficient of line tension between membrane domains of different composition. The model system in our simulations consists of lipid bilayers containing dipalmitoyl phosphatidyl choline (DPPC) mixed with phosphatidylinositol-4-phosphate (PI4P) or phosphatidylinositol-4,5-bisphosphate (PIP2). We will then show the equilibrium vesicle shapes corresponding to various membrane compositions by mapping the elastic parameters obtained from MD simulations onto existing macroscopic elastic models.