Sec-dependent preprotein translocation in bacteria |
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Authors: | Tanneke den Blaauwen A J M Driessen |
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Institution: | (1) Department of Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands Tel. +31-50-632164; Fax +31-50-632154 e-mail: a.j.m.driessen@biol.rug.nl, NL |
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Abstract: | Translocation of precursor proteins across the cytoplasmic membrane in bacteria is mediated by a multi-subunit protein complex
termed translocase, which consists of the integral membrane heterotrimer SecYEG and the peripheral homodimeric ATPase SecA.
Preproteins are bound by the cytosolic molecular chaperone SecB and targeted in a complex with SecA to the translocation site
at the cytoplasmic membrane. This interaction with SecYEG allows the SecA/preprotein complex to insert into the membrane by
binding of ATP to the high affinity nucleotide binding site of SecA. At that stage, presumably recognition and proofreading
of the signal sequence occurs. Hydrolysis of ATP causes the release of the preprotein in the translocation channel and drives
the withdrawal of SecA from the membrane-integrated state. Hydrolysis of ATP at the low-affinity nucleotide binding site of
SecA converts the protein into a compact conformational state and releases it from the membrane. In the absence of the proton
motive force, SecA is able to complete the translocation stepwise by multiple nucleotide modulated cycles.
Received: 4 August 1995 / Accepted: 9 October 1995 |
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Keywords: | Escherichia coli ATPase Energetics Membrane protein Protein folding Sec Proteins Transport |
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