Structure and Dynamics of the Full-Length Lipid-Modified H-Ras Protein in a 1,2-Dimyristoylglycero-3-phosphocholine Bilayer

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Abstract
Ras proteins regulate signal transduction processes that control cell growth and proliferation. Their disregulation is a common cause of human tumors. Atomic level structural and dynamical information in a membrane environment is crucial for understanding signaling specificity among Ras isoforms and for the design of selective anti-cancer agents. Here, the structure of the full-length H-Ras protein in complex with a 1,2-dimyristoylglycero-3-phosphocholine (DMPC) bilayer obtained from modeling and all-atom explicit solvent molecular dynamics simulations, as well as experimental validation of the main results, are presented. We find that, in addition to the lipid anchor, H-Ras membrane binding involves direct interaction of residues in the catalytic domain with DMPC phosphates. Two modes of binding (possibly modulated by GTP/GDP exchange) differing in the orientation and bilayer contact of the soluble domain as well as in the participation of the flexible linker in membrane binding are proposed. These results are supported by our initial in vivo experiments. The overall structures of the protein and the bilayer remain similar to those of the isolated components, with few localized structural and dynamical changes. The implications of the results to membrane lateral segregation and other aspects of Ras signaling are discussed.