Cotranslational protein integration into the ER membrane is mediated by the binding of nascent chains to translocon proteins.
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.
McCormick
Peter J
PJ
Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843, USA.
Miao
Yiwei
Y
Shao
Yuanlong
Y
Lin
Jialing
J
Johnson
Arthur E
AE
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
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