Moritz Frewein will give a seminar on the “Interleaflet coupling in Asymmetric Lipid membranes”
on Monday, October 3, at 11:00 a.m. in the Espace photonique meeting room
Abstract :
Cellular envelopes contain a large number of lipid species that are distributed asymmetrically between the two leaflets of the bilayer. In particular, prototypical mammalian plasma membranes are known to be composed of an outer leaflet enriched in cholinephospholipids, while the majority of the aminophospholipids are confined to the inner leaflet. One of the enduring questions of plasma membrane architecture and lipid asymmetry concerns the possibility of interleaflet coupling even in the absence of proteins, which may influence membrane structure, mechanical properties and a number of physiological processes. Currently conceived lipid-mediated coupling mechanisms consider either intrinsic lipid curvature, headgroup electrostatics, cholesterol flip-flop, dynamic chain interdigitation, thermal membrane fluctuations or differential stress. We characterized large unilamellar lipid vesicles by small-angle neutron and X-ray scattering to detect hydrocarbon chain interdigitation of mixed-chain phosphocholines and found a large change in structure if lipids are arranged asymmetrically. In the next step we added aminophospholipids to the inner leaflet and measured also the bilayer stiffness using neutron spin-echo spectroscopy. The result was a dramatic increase in rigidity when lipids are arranged asymmetrically, in particular for systems which closely mimic the plasma membrane composition. As we did not detect changes in structure, which clearly correlate with this effect, we suggest that the bilayer stiffness is determined by specific lipid interactions arising from differences in the bilayer undulatory motions.
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