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