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Biol Chem. 1999 Oct;380(10):1143-50.

Posttranslational protein translocation across the membrane of the endoplasmic reticulum.

Author information

1
Howard Hughes Medical Institute and Department of Cell Biology, Harvard Medical School, Boston, MA 02115-6091, USA.

Abstract

Posttranslational protein translocation across the membrane of the endoplasmic reticulum is mediated by the Sec complex. This complex includes a transmembrane channel formed by multiple copies of the Sec61 protein. Translocation of a polypeptide begins when the signal sequence binds at a specific site within the channel. Binding results in the insertion of the substrate into the channel, possibly as a loop with a small segment exposed to the lumen. While bound, the signal sequence is in contact with both protein components of the channel and the lipid of the membrane. Subsequent movement of the polypeptide through the channel occurs when BiP molecules interact transiently with a luminal domain of the Sec complex, hydrolyze ATP, and bind to the substrate. Bound BiP promotes translocation by preventing the substrate from diffusing backwards through the channel, and thus acts as a molecular ratchet.

PMID:
10595576
DOI:
10.1515/BC.1999.145
[Indexed for MEDLINE]

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