Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 106, Issue 49, Pages 20800-20805Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0910550106
Keywords
disulfide bridge cross-linking; protein translocation; SecY; secretion; SecA clamp
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Funding
- National Institutes of Health [GM052586]
- Austrian Marshall Plan Foundation
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Many 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.
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