标题：Be straight to better coordinate two -- Head groups and extended acyl chains of raft-like bilayer lipids can localize in groove between dimerized transmembrane helical peptides and assist sequence-nonspecific stabilization of peptide dimers by cholesterol
摘要：An increase in the cholesterol content in phospholipid bilayer membranes is known to engender high order structures of lipids, which involve straightened (extended) lipid acyl chains. Lipid rafts are rich in such extended chains and considered to help clustering/multimerization of transmembrane helical peptides. Our recent atomistic simulations showed that the dimeric state of model helical peptides is stabilized in raft-like bilayers and that the potential energy term ascribed to lipid-peptide interactions contributes to the stabilization. Here our computation shows that the number of those lipids atoms which simultaneously contacted with both helical peptides in the dimeric state (which we refer to as 'dual contacts') was greater for a raft-like bilayer (1:1:1 palmitoyloleoylphosphatidylcholine (POPC)/dipalmitoylphosphatidylcholine (DPPC)/cholesterol bilayer) compared to a dioleoylphosphatidylcholine (DOPC) bilayer. Specifically, the distal half (i.e., near the CH3-terminal) of the acyl chains as well as the phospholipids head groups showed such differences. The number of the lipid atoms with such dual contacts was associated with the unsigned value of lipid-peptide term of the potential energy. Thus, the extended structures of saturated acyl chains in raft-like bilayers appear to enable phospholipids molecules to reside in the groove between, and contact with, both peptides in the dimeric/multimeric state, thereby modulating the potential energy in favor of the dimeric/multimeric state in a sequence-nonspecific manner. The formation of such dual contacts is likely to be assisted by small tilt and helix-helix crossing angles of the dimerized peptides which also appear to be brought about by extended acyl chains in the raft-like bilayer.
