Average Conformation of Branched-Chain Lipid PGP-Me that Accounts for the Thermal Stability and High-Salinity Registance of Archaeal Membranes

Masaki Yamagami, Hiroshi Tsuchikawa*, Jin Cui, Yuichi Umegawa, Yusuke Miyazaki, Sangjae Seo, Wataru Shinoda*, Michio Murata*

The average conformation of the methyl-branched chains of archaeal lipid, phosphatidyl glycerophosphate methyl ester (PGP-Me), was examined in a hydrated bilayer membrane based on the ²H NMR of enantioselectively ²H-labeled compounds that were totally synthesized for the first time in this study. The NMR results in combination with molecular dynamics simulations revealed that the PGP-Me chain appeared to behave differently from that of typical membrane lipids such as dipalmitoylphosphatidylcholine (DMPC). The C-C bonds of the PGP-Me chain adopt alternative parallel and tilted orientations to the membrane normal as opposed to a DMPC chain where all of the C-C bonds tilt in the same way on average. This characteristic orientation causes the intertwining of PGP-Me chains, which plays an important role in the excellent thermal and high-salinity stabilities of archaeal lipid bilayers and membrane proteins.