title: Mechanisms of membrane binding of small GTPase K-Ras4B farnesylated hypervariable region.
abstract: K-Ras4B belongs to a family of small GTPases that regulates cell growth, differentiation and survival. K-ras is frequently mutated in cancer. K-Ras4B association with the plasma membrane through its farnesylated and positively charged C-terminal hypervariable region (HVR) is critical to its oncogenic function. However, the structural mechanisms of membrane association are not fully understood. Here, using confocal microscopy, surface plasmon resonance, and molecular dynamics simulations, we observed that K-Ras4B can be distributed in rigid and loosely packed membrane domains. Its membrane binding domain interaction with phospholipids is driven by membrane fluidity. The farnesyl group spontaneously inserts into the disordered lipid microdomains, whereas the rigid microdomains restrict the farnesyl group penetration. We speculate that the resulting farnesyl protrusion toward the cell interior allows oligomerization of the K-Ras4B membrane binding domain in rigid microdomains. Unlike other Ras isoforms, K-Ras4B HVR contains a single farnesyl modification and positively charged polylysine sequence. The high positive charge not only modulates specific HVR binding to anionic phospholipids but farnesyl membrane orientation. Phosphorylation of Ser-181 prohibits spontaneous farnesyl membrane insertion. The mechanism illuminates the roles of HVR modifications in K-Ras4B targeting microdomains of the plasma membrane and suggests an additional function for HVR in regulation of Ras signaling.
authors.affiliation: From the Basic Science Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research and Cancer and Inflammation Program, NCI-Frederick, National Institutes of Health, Frederick, Maryland 21702.
authors.forename: Hyunbum
authors.initials: H
authors.lastname: Jang
authors.affiliation: Department of Molecular and Cellular Physiology, Stanford University, Stanford, California 94305, Departments of Biochemistry and Molecular Genetics and.
authors.forename: Sherwin J
authors.initials: SJ
authors.lastname: Abraham
authors.affiliation: Department of Molecular and Cellular Physiology, Stanford University, Stanford, California 94305, Medicinal Chemistry, University of Illinois, Chicago, Illinois 60607, and.
authors.forename: Tanmay S
authors.initials: TS
authors.lastname: Chavan
authors.affiliation: Departments of Biochemistry and Molecular Genetics and.
authors.forename: Ben
authors.initials: B
authors.lastname: Hitchinson
authors.affiliation: From the Basic Science Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research and Cancer and Inflammation Program, NCI-Frederick, National Institutes of Health, Frederick, Maryland 21702.
authors.forename: Lyuba
authors.initials: L
authors.lastname: Khavrutskii
authors.affiliation: Cancer and Inflammation Program, NCI-Frederick, National Institutes of Health, Frederick, Maryland 21702, Nadya.Tarasova@nih.gov.
authors.forename: Nadya I
authors.initials: NI
authors.lastname: Tarasova
authors.affiliation: From the Basic Science Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research and Cancer and Inflammation Program, NCI-Frederick, National Institutes of Health, Frederick, Maryland 21702, Department of Human Molecular Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel NussinoR@helix.nih.gov.
authors.forename: Ruth
authors.initials: R
authors.lastname: Nussinov
authors.affiliation: Departments of Biochemistry and Molecular Genetics and Medicinal Chemistry, University of Illinois, Chicago, Illinois 60607, and vadimg@uic.edu.
authors.forename: Vadim
authors.initials: V
authors.lastname: Gaponenko
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D008560:Membrane Fluidity; D021962:Membrane Microdomains / Q000737:chemistry / Q000378:metabolism; D018613:Microscopy, Confocal; D008956:Models, Chemical; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010743:Phospholipids / Q000737:chemistry / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D055503:Protein Multimerization; D017368:Protein Prenylation; D016283:Proto-Oncogene Proteins p21(ras) / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012694:Serine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020349:Surface Plasmon Resonance
chemical_list: C117307:KRAS protein, human; D008051:Lipid Bilayers; D010455:Peptides; D010743:Phospholipids; D012694:Serine; D020558:GTP Phosphohydrolases; D016283:Proto-Oncogene Proteins p21(ras)
keywords: Cooperativity; HVR; Membrane Microdomains; Phospholipid; Phosphorylation; Post-translational Modification (PTM); Protein Isoprenylation