  In spite of the great success that all-atom molecular dynamics simulations
have seen in revealing the nature of the lipid bilayer, the interplay between a
membrane's curvature and dynamics remains elusive. This is largely due to the
computational challenges involved in simulating a highly curved membrane, as
the one found in a small vesicle. In the present work, thanks to the computing
power of Anton2, we present the first all-atom molecular dynamics simulation of
a full-scale, realistically composed (both heterogeneous and asymmetric)
vesicle of a meaningful time scale (over 10 microseconds), which reveals unique
biophysical properties of various lipid molecules (diffusion coefficients,
surface areas per lipid, order parameters) and packing defects in a highly
curved environment. Most interestingly, a bilayer of the same lipid composition
demonstrating no phase coexistence when flat shows very strong indictors of
phase coexistence when highly curved. Lipid molecules found in the
curvature-induced different phases are carefully verified by their distinct
composition, area per lipid, parking defects, as well as diffusion coefficient.
The result of the all-atom molecular dynamics simulations is consistent with
previous experimental and theoretical models and enhance the understanding of
nanoscale dynamics and membrane organization of small, highly curved
organelles.
