Sec-dependent preprotein translocation in bacteria.
Translocation of precursor proteins across the cytoplasmic membrane in bacteria is mediated by a multisubunit protein complex termed translocase, which consists of the integral membrane heterotrimer Sec YEG 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 Sec YEG 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.
den Blaauwen
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Department of Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, The Netherlands.
Driessen
A J
AJ
D000251:Adenosine Triphosphatases / Q000502:physiology*; D000595:Amino Acid Sequence; D001419:Bacteria / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism* / Q000502:physiology*; D001692:Biological Transport; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D011498:Protein Precursors / Q000378:metabolism*; D000069816:SEC Translocation Channels; D000081416:SecA Proteins
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D011498:Protein Precursors; D000069816:SEC Translocation Channels; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins