title: Cotranslational protein integration into the ER membrane is mediated by the binding of nascent chains to translocon proteins.
abstract: During cotranslational protein integration into the ER membrane, each transmembrane (TM) segment moves laterally through the translocon to reach the lipid bilayer. Photocrosslinking studies reveal that a particular surface of each nascent chain TM alpha helix and signal-anchor sequence always faces Sec61alpha in the translocon. This nonrandom and TM sequence-dependent positioning reveals that each TM segment makes specific contacts with Sec61alpha and is retained at a fixed location within the translocon, observations that are best explained by the binding of each TM sequence to a translocon protein(s). Since TM sequence hydrophobicity does not correlate with its rate of release from the translocon, nascent chain movement through the translocon appears to be mediated primarily by protein-protein interactions rather than hydrophobic nascent chain-phospholipid interactions.
authors.affiliation: Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843, USA.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: McCormick
authors.forename: Yiwei
authors.initials: Y
authors.lastname: Miao
authors.forename: Yuanlong
authors.initials: Y
authors.lastname: Shao
authors.forename: Jialing
authors.initials: J
authors.lastname: Lin
authors.forename: Arthur E
authors.initials: AE
authors.lastname: Johnson
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism; D001665:Binding Sites; D003432:Cross-Linking Reagents / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism*; D008027:Light; D008051:Lipid Bilayers / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008954:Models, Biological; D010743:Phospholipids / Q000737:chemistry; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D014176:Protein Biosynthesis; D021381:Protein Transport; D011506:Proteins / Q000737:chemistry*; D012333:RNA, Messenger / Q000378:metabolism; D012343:RNA, Transfer / Q000378:metabolism; D000069816:SEC Translocation Channels
chemical_list: D001426:Bacterial Proteins; D003432:Cross-Linking Reagents; D008051:Lipid Bilayers; D008565:Membrane Proteins; D010743:Phospholipids; D011506:Proteins; D012333:RNA, Messenger; D000069816:SEC Translocation Channels; C074281:TraM protein, bacterial; D012343:RNA, Transfer