Bacterial preprotein translocase: mechanism and conformational dynamics of a processive enzyme.
Preprotein translocase, the membrane transporter for secretory proteins, is a processive enzyme. It comprises the membrane proteins SecYEG(DFYajC) and the peripheral ATPase SecA, which acts as a motor subunit. Translocase subunits form dynamic complexes in the lipid bilayer and build an aqueous conduit through which preprotein substrates are transported at the expense of energy. Preproteins bind to translocase and trigger cycles of ATP binding and hydrolysis that drive a transition of SecA between two distinct conformational states. These changes are transmitted to SecG and lead to inversion of its membrane topology. SecA conformational changes promote directed migration of the polymeric substrate through the translocase, in steps of 20-30 aminoacyl residues. Translocase dissociates from the substrate only after the whole preprotein chain length has been transported to the trans side of the membrane, where it is fully released.
Economou
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Institute of Molecular Biology and Biotechnology-FORTH and Department of Biology, University of Crete, Iraklio-Crete, Greece. aeconomou@imbb.forth.gr
D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D001692:Biological Transport; D002462:Cell Membrane / Q000201:enzymology; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D011487:Protein Conformation; D018892:Proton-Motive Force; D000069816:SEC Translocation Channels; D000081416:SecA Proteins
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D000069816:SEC Translocation Channels; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins