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J. Biol. Chem., Vol. 282, Issue 2, 1281-1287, January 12, 2007

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Deregulation of the SecYEG Translocation Channel upon Removal of the Plug Domain^*

Antoine P. Maillard¹, Shifana Lalani, Filo Silva, Dominique Belin, and Franck Duong, Supported by the Canada Research Chair program²

From the Department of Biochemistry and Molecular Biology, Life Sciences Institute, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia V6T1Z3, Canada and the Department of Pathology and Immunology, University of Geneva, 1 rue Michel-Servet, CH-1211 Geneva, Switzerland

Previous studies have shown that the SecY plug is displaced from the center of the SecYEG channel during polypeptide translocation. The structural and functional consequences of the deletion of the plug are now examined. Both in vivo and in vitro observations indicate that the plug domain is not essential to the function of the translocon. In fact, deletion of the plug confers to the cell and to the membranes a Prl-like phenotype: reduced proton-motive force dependence of translocation, increased membrane insertion of SecA, diminished requirement for functional leader peptide, and weakened SecYEG subunit association. Although the plug domain does not seem essential, locking the plug in the center of the channel inactivates the translocon. Thus, the SecY plug is important to regulate the activity of the channel and to confer specificity to the translocation reaction. We propose that the plug contributes to the gating mechanism of the channel by maintaining the structure of the SecYEG complex in a compact closed state.

Received for publication, October 27, 2006

^* This work was supported by grants from the Fonds National Suisse (to D. B.) and from the Canadian Fund for Innovation and the Canadian Institutes of Health Research (CIHR) (to F. D.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Recipient of a scholarship from the INSERM-CIHR joint program. Present address: Institut de Virologie Moléculaire et Structurale, Université Joseph Fourier–EMBL, 6 rue Jules Horowitz, B.P. 181, 38042, Grenoble cedex 9, France.

² To whom correspondence should be addressed: Dept. of Biochemistry and Molecular Biology, Faculty of Medicine, Life Sciences Institute, University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC, V6T 1Z3, Canada. Tel.: 604-822-5975; Fax: 604-822-5227; E-mail: FDuong{at}interchange.ubc.ca.

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