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J. Biol. Chem., Vol. 283, Issue 48, 33267-33275, November 28, 2008

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Following the Path of a Twin-arginine Precursor along the TatABC Translocase of Escherichia coli^*

Sascha Panahandeh, Carlo Maurer, Michael Moser, Matthew P. DeLisa^¶, and Matthias Müller¹

From the Institut für Biochemie und Molekularbiologie, ZBMZ, and the Fakultät für Biologie, Universität Freiburg, D-79104 Freiburg, Germany and the ^¶School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853

The twin-arginine translocation (Tat) machinery present in bacterial and thylakoidal membranes is able to transport fully folded proteins. Consistent with previous in vivo data, we show that the model Tat substrate TorA-PhoA is translocated by the TatABC translocase of Escherichia coli inner membrane vesicles, only if the PhoA moiety was allowed to fold by disulfide bond formation. Although even unfolded TorA-PhoA was found to physically associate with the Tat translocase of the vesicles, site-specific cross-linking revealed a perturbed interaction of the signal sequence of unfolded TorA-PhoA with the TatBC receptor site. Some of the folded TorA-PhoA precursor accumulated in a partially protease-protected membrane environment, from where it could be translocated into the lumen of the vesicles upon re-installation of an H⁺-gradient. Translocation arrest occurred in immediate vicinity to TatA. Consistent with a neighborhood to TatA, TorA-PhoA remained protease-resistant in the presence of detergents that are known to preserve the oligomeric structures of TatA. Moreover, entry of TorA-PhoA to the protease-protected environment strictly required the presence of TatA. Collectively, our results are consistent with some degree of quality control by TatBC and a recruitment of TatA to a folded substrate that has functionally engaged the twin-arginine translocase.

Received for publication, June 2, 2008 , and in revised form, September 25, 2008.

^* This work was supported by Grant LSHG-CT-2004-005257 of the European Union (to S. P. and M. M.), grants from the Deutsche Forschungsgemeinschaft (Collaborative Research Centres 388 and 746, to M. M.), an F.F. Nord fellowship of the University of Freiburg (to C. M.), and an NSF Career Award (CBET 0449080) and a NYSTAR James D. Watson Award (both to M. P. 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 To whom correspondence should be addressed. Tel.: 49-761-203-5265; Fax: 49-761-203-5274; E-mail: matthias.mueller{at}biochemie.uni-freiburg.de.

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