title: Transmembrane helices before, during, and after insertion.
abstract: The transmembrane (TM) helix is the fundamental structural unit of helix-bundle membrane proteins. Recent biophysical studies provide new insights into the interactions of TM helices with each other and with membrane lipid bilayers. The biological process of helix insertion is carried out by translocon complexes acting in concert with ribosomes. An electron cryo-microscopic reconstruction of these complexes reveals their architecture in new detail, and shows that the complex is constructed from four SecY/Sec61 heterotrimers and two TRAP complexes. A disulfide bridge study shows that elongating polypeptide chains pass through the pore previously identified in the X-ray structure of an archaeal SecY heterotrimer. The fundamental code used by the translocon to select polypeptide segments for insertion as TM helices has been broken. A detailed analysis of the TM amino acid distributions of helix-bundle membrane proteins of known structure recapitulates this code.
authors.affiliation: Department of Physiology and Biophysics, and Program in Macromolecular Structure, University of California at Irvine, Irvine, CA 92697-4560, USA. blanco@helium.biomol.uci.edu
authors.forename: Stephen H
authors.initials: SH
authors.lastname: White
authors.forename: Gunnar
authors.initials: G
authors.lastname: von Heijne
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism*; D020285:Cryoelectron Microscopy; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D000069816:SEC Translocation Channels
chemical_list: D008051:Lipid Bilayers; D046911:Macromolecular Substances; D008565:Membrane Proteins; D010455:Peptides; D000069816:SEC Translocation Channels