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J. Biol. Chem., Vol. 282, Issue 11, 7903-7911, March 16, 2007

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Escherichia coli Twin Arginine (Tat) Mutant Translocases Possessing Relaxed Signal Peptide Recognition Specificities^*

From the Institut für Biotechnologie 1, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany

The twin arginine (Tat) secretion pathway allows the translocation of folded proteins across the cytoplasmic membrane of bacteria. Tat-specific signal peptides contain a characteristic amino acid motif ((S/T)RRXFLK) including two highly conserved consecutive arginine residues that are thought to be involved in the recognition of the signal peptides by the Tat translocase. Here, we have analyzed the specificity of Tat signal peptide recognition by using a genetic approach. Replacement of the two arginine residues in a Tat-specific precursor protein by lysine-glutamine resulted in an export-defective mutant precursor that was no longer accepted by the wild-type translocase. Selection for restored export allowed for the isolation of Tat translocases possessing single mutations in either the amino-terminal domain of TatB or the first cytosolic domain of TatC. The mutant Tat translocases still efficiently accepted the unaltered precursor protein, indicating that the substrate specificity of the translocases was not strictly changed; rather, the translocases showed an increased tolerance toward variations of the amino acids occupying the positions of the twin arginine residues in the consensus motif of a Tat signal peptide.

Received for publication, October 30, 2006 , and in revised form, January 16, 2007.

^* This work was supported by European Union Grant LSHG-CT-2004-005257 and by Deutsche Forschungsgemeinschaft Grant Sp503/2-2. 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 Present address: Roche Diagnostics, Pharmaceutical Biotech Production and Development, Nonnenwald 2, 82377 Penzberg, Germany.

² Present address: ZIEL-Abteilung Mikrobiologie, Technische Universität München, Weihenstephaner Berg 3, 85350 Freising, Germany.

³ Present address: Institut für vegetative Physiologie, Universität zu Köln, Robert-Koch-Str. 39, 50931 Köln, Germany.

⁴ Present address: Institut für Mikrobiologie, Universität Stuttgart, Allmandring 31, 70569 Stuttgart, Germany.

⁵ To whom correspondence should be addressed. Tel.: 49-2461-613472; Fax: 49-2461-612710; E-mail: r.freudl{at}fz-juelich.de.

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