Mechanical
Properties of Nanoscopic Lipid Domains
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Abstract
The lipid raft hypothesis presents
insights into how the cell membrane
organizes proteins and lipids to accomplish its many vital functions.
Yet basic questions remain about the physical mechanisms that lead
to the formation, stability, and size of lipid rafts. As a result,
much interest has been generated in the study of systems that contain
similar lateral heterogeneities, or domains. In the current work we
present an experimental approach that is capable of isolating the
bending moduli of lipid domains. This is accomplished using neutron
scattering and its unique sensitivity to the isotopes of hydrogen.
Combining contrast matching approaches with inelastic neutron scattering,
we isolate the bending modulus of ∼13 nm diameter domains residing
in 60 nm unilamellar vesicles, whose lipid composition mimics the
mammalian plasma membrane outer leaflet. Importantly, the bending
modulus of the nanoscopic domains differs from the modulus of the
continuous phase surrounding them. From additional structural measurements
and all-atom simulations, we also determine that nanoscopic domains
are in-register across the bilayer leaflets. Taken together, these
results inform a number of theoretical models of domain/raft formation
and highlight the fact that mismatches in bending modulus must be
accounted for when explaining the emergence of lateral heterogeneities
in lipid systems and biological membranes