Bauer, Benedikt W.Rapoport, Tom A.2019-10-142009Bauer, B. W., and T. A. Rapoport. 2009. “Mapping Polypeptide Interactions of the SecA ATPase during Translocation.” Proceedings of the National Academy of Sciences 106 (49): 20800–805. doi:10.1073/pnas.0910550106.0027-84240744-28311091-6490http://nrs.harvard.edu/urn-3:HUL.InstRepos:41543114Many bacterial proteins, including most secretory proteins, are translocated across the plasma membrane by the interplay of the cytoplasmic SecA ATPase and a protein-conducting channel formed by the SecY complex. SecA catalyzes the sequential movement of polypeptide segments through the SecY channel. How SecA interacts with a broad range of polypeptide segments is unclear, but structural data raise the possibility that translocation substrates bind into a "clamp'' of SecA. Here, we have used disulfide bridge cross-linking to test this hypothesis. To analyze polypeptide interactions of SecA during translocation, two cysteines were introduced into a translocation intermediate: one that cross-links to the SecY channel and the other one for cross-linking to a cysteine placed at various positions in SecA. Our results show that a translocating polypeptide is indeed captured inside SecA's clamp and moves in an extended conformation through the clamp into the SecY channel. These results define the polypeptide path during SecA-mediated protein translocation and suggest a mechanism by which ATP hydrolysis by SecA is used to move a polypeptide chain through the SecY channel.en-USJournal Article2019-10-1410.1073/pnas.0910550106