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Mol Cell. 2013 Dec 12;52(5):655-66. doi: 10.1016/j.molcel.2013.10.036.

Quaternary dynamics of the SecA motor drive translocase catalysis.

Author information

1
Institute of Molecular Biology and Biotechnology (FORTH), University of Crete, P.O. Box 1385, Iraklio, Crete 71110, Greece.
2
Institute of Molecular Biology and Biotechnology (FORTH), University of Crete, P.O. Box 1385, Iraklio, Crete 71110, Greece; Rega Institute, Department of Microbiology and Immunology, KU Leuven, 3000 Leuven, Belgium.
3
Institute of Molecular Biology and Biotechnology (FORTH), University of Crete, P.O. Box 1385, Iraklio, Crete 71110, Greece; Department of Biology, University of Crete, P.O. Box 1385, Iraklio, Crete 71110, Greece.
4
Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland.
5
Institute of Molecular Biology and Biotechnology (FORTH), University of Crete, P.O. Box 1385, Iraklio, Crete 71110, Greece; Department of Biology, University of Crete, P.O. Box 1385, Iraklio, Crete 71110, Greece; Rega Institute, Department of Microbiology and Immunology, KU Leuven, 3000 Leuven, Belgium. Electronic address: tassos.economou@rega.kuleuven.be.

Abstract

Most secretory preproteins exit bacterial cells through the protein translocase, comprising the SecYEG channel and the dimeric peripheral ATPase motor SecA. Energetic coupling to work remains elusive. We now demonstrate that translocation is driven by unusually dynamic quaternary changes in SecA. The dimer occupies several successive states with distinct protomer arrangements. SecA docks on SecYEG as a dimer and becomes functionally asymmetric. Docking occurs via only one protomer. The second protomer allosterically regulates downstream steps. Binding of one preprotein signal peptide to the SecYEG-docked SecA protomer elongates the SecA dimer and triggers the translocase holoenzyme to obtain a lower activation energy conformation. ATP hydrolysis monomerizes the triggered SecA dimer, causing mature chain trapping and processive translocation. This is a unique example of one protein exploiting quaternary dynamics to become a substrate receptor, a "loading clamp," and a "processive motor." This mechanism has widespread implications on protein translocases, chaperones, and motors.

PMID:
24332176
DOI:
10.1016/j.molcel.2013.10.036
[Indexed for MEDLINE]
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