Proceedings of the National Academy of Sciences of the United States of America
SecA, a 102-kDa hydrophilic protein, couples the energy of ATP binding to the translocation of preprotein across the bacterial inner membrane. SecA function and topology were studied with metabolically labeled [35S]SecA and with inner membrane vesicles from cells that overex- pressed SecYEGDFyajC, the integral domain of preprotein translocase. During translocation in the presence of ATP and preprotein, a 65-kDa N-terminal domain of SecA is protected from proteolytic digestion through insertion into the mem- brane, as previously reported for a 30-kDa C-terminal domain [Economou, A. & Wickner, W. (1994) Cell 78, 835–843]. Insertion of both domains occurs at saturable SecYEGDFyajC sites and is rapidly followed by deinsertion. SecA also asso- ciates nonsaturably and unproductively with lipid. In the presence of ATP, yet without involvement of preprotein or SecYEG, lipid-bound SecA forms domains that are protease- resistant and that remain so even upon subsequent membrane disruption. Unlike the [35S]SecA that inserts into the mem- brane at SecYEGDFyajC as it promotes preprotein translo- cation, lipid-associated [35S]SecA does not chase from its protease-resistant state upon the addition of excess SecA. The finding that two domains of SecA (which together represent most regions of the polypeptide chain) cycle into the mem- brane during preprotein translocation, as well as the distinc- tion between the membrane association of SecA at transloca- tion sites of SecYEGDFyajC and at nonproductive lipid sites, are fundamental to the study of the role of SecA in preprotein movement.
Dartmouth Digital Commons Citation
Eichler, Jerry and Wickner, William, "Both an N-Terminal 65-Kda Domain and a C-Terminal 30-Kda Domain of Seca Cycle into the Membrane at Secyeg During Translocation" (1997). Open Dartmouth: Peer-reviewed articles by Dartmouth faculty. 2034.