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J. Biol. Chem., Vol. 282, Issue 10, 7116-7124, March 9, 2007

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DnaK Plays a Pivotal Role in Tat Targeting of CueO and Functions beside SlyD as a General Tat Signal Binding Chaperone^*

Wenke Graubner, Angelika Schierhorn, and Thomas Brüser¹

From the Institute of Microbiology, University of Halle-Wittenberg, Kurt-Mothes-Strasse 3, D-06120 Halle, Germany and Max Planck Research Unit for Enzymology of Protein Folding, Weinbergweg 22, D-06120 Halle, Germany

The Tat (twin-arginine translocation) system from Escherichia coli transports folded proteins with N-terminal twin-arginine signal peptides across the cytoplasmic membrane. The influence of general chaperones on Tat substrate targeting has not been clarified so far. Here we show that the chaperones SlyD and DnaK bind to a broad range of different Tat signal sequences in vitro and in vivo. Initially, SlyD and GroEL were purified from DnaK-deficient extracts by their affinity to various Tat signal sequences. Of these, only SlyD bound Tat signal sequences also in the presence of DnaK. SlyD and DnaK also co-purified with Tat substrate precursors, demonstrating the binding to Tat signal sequences in vivo. Deletion of dnaK completely abolished Tat-dependent translocation of CueO, but not of DmsA, YcdB, or HiPIP, indicating that DnaK has an essential role specifically for CueO. DnaK was not required for stability of the CueO precursor and thus served in some essential step after folding. A CueO signal sequence fusion to HiPIP was Tat-dependently transported without the need of DnaK, indicating that the mature domain of CueO is responsible for the DnaK dependence. The overall results suggest that SlyD and DnaK are in the set of chaperones that can serve as general Tat signal-binding proteins. DnaK has additional functions that are indispensable for the targeting of CueO.

Received for publication, August 28, 2006 , and in revised form, January 5, 2007.

^* This work was supported by Deutsche Forschungsgemeinschaft Grant BR2285/1-3, the state Sachsen-Anhalt (Exzellenzcluster Biowissenschaften), and the Fonds der Chemischen Industrie (to T. B.). 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.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. S1–S3.

¹ To whom correspondence should be addressed: Institute of Microbiology, Martin-Luther-Universität Halle-Wittenberg, Kurt-Mothes-Str. 3, D-06120 Halle, Germany. Tel.: 49-345-5526360; E-mail: t.brueser{at}mikrobiologie.uni-halle.de.

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