A molecular switch in SecA protein couples ATP hydrolysis to protein translocation.
SecA, the dimeric ATPase subunit of bacterial protein translocase, catalyses translocation during ATP-driven membrane cycling at SecYEG. We now show that the SecA protomer comprises two structural modules: the ATPase N-domain, containing the nucleotide binding sites NBD1 and NBD2, and the regulatory C-domain. The C-domain binds to the N-domain in each protomer and to the C-domain of another protomer to form SecA dimers. NBD1 is sufficient for single rounds of SecA ATP hydrolysis. Multiple ATP turnovers at NBD1 require both the NBD2 site acting in cis and a conserved C-domain sequence operating in trans. This intramolecular regulator of ATP hydrolysis (IRA) mediates N-/C-domain binding and acts as a molecular switch: it suppresses ATP hydrolysis in cytoplasmic SecA while it releases hydrolysis in SecY-bound SecA during translocation. We propose that the IRA switch couples ATP binding and hydrolysis to SecA membrane insertion/deinsertion and substrate translocation by controlling nucleotide-regulated relative motions between the N-domain and the C-domain. The IRA switch is a novel essential component of the protein translocation catalytic pathway.
Karamanou
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Institute of Molecular Biology and Biotechnology and Department of Biology, University of Crete, PO Box 1527, GR-711 10 Iraklio, Crete, Greece.
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Sianidis
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D000244:Adenosine Diphosphate / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D002942:Circular Dichroism; D017124:Conserved Sequence; D019281:Dimerization; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D006868:Hydrolysis; D007700:Kinetics; D008565:Membrane Proteins / Q000378:metabolism; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D016296:Mutagenesis; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D000069816:SEC Translocation Channels; D000081416:SecA Proteins
D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D000069816:SEC Translocation Channels; C057841:SecY protein, E coli; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins