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| The EMBO Journal
(1998) 17, 101–112, doi:10.1093/emboj/17.1.101 |
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| A novel Sec-independent periplasmic protein translocation pathway in Escherichia coli |
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| Claire-Lise Santini1, Bérengère Ize1, Angélique Chanal1, Matthias Müller2, Gérard Giordano1 and Long-Fei Wu1 |
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1 Laboratoire de Chimie Bactérienne, UPR9043 CNRS, Institut de Biologie Structurale et Microbiologie, 31 chemin Joseph Aiguier, 13402 Marseille cedex 20, France 2 Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Strasse 7, D-79104 Freiburg, Germany To whom correspondence should be addressed Long-Fei Wu, wu@ibsm.cnrs-mrs.fr Received 15 July 1997; Revised 22 September 1997; Accepted 10 October 1997. |
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| Abstract |
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| The trimethylamine N-oxide (TMAO) reductase of Escherichia coli is a soluble periplasmic molybdoenzyme. The precursor of this enzyme possesses a cleavable N-terminal signal sequence which contains a twin-arginine motif. By using various moa, mob and mod mutants defective in different steps of molybdocofactor biosynthesis, we demonstrate that acquisition of the molybdocofactor in the cytoplasm is a prerequisite for the translocation of the TMAO reductase. The activation and translocation of the TMAO reductase precursor are post-translational processes, and activation is dissociable from translocation. The export of the TMAO reductase is driven mainly by the proton motive force, whereas sodium azide exhibits a limited effect on the export. The most intriguing observation is that translocation of the TMAO reductase across the cytoplasmic membrane is independent of the SecY, SecE, SecA and SecB proteins. Depletion of Ffh, a core component of the signal recognition particle of E.coli, appears to have a slight effect on the export of the TMAO reductase. These results strongly suggest that the translocation of the molybdoenzyme TMAO reductase into the periplasm uses a mechanism fundamentally different from general protein translocation. |
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| Keywords: metalloenzyme, periplasm, Sec system, signal recognition particle, twin-arginine motif |
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