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J. Biol. Chem., Vol. 283, Issue 7, 4124-4132, February 15, 2008

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Dynamics of Trigger Factor Interaction with Translating Ribosomes^*

Anna Rutkowska, Matthias P. Mayer, Anja Hoffmann, Frieder Merz, Beate Zachmann-Brand, Christiane Schaffitzel, Nenad Ban, Elke Deuerling¹, and Bernd Bukau²

From the Zentrum für Molekulare Biologie Heidelberg, University of Heidelberg, Heidelberg 69120, Germany and Institut für Molekularbiologie und Biophysik, ETH Zürich, CH-8093 Zürich, Switzerland

In all organisms ribosome-associated chaperones assist early steps of protein folding. To elucidate the mechanism of their action, we determined the kinetics of individual steps of the ribosome binding/release cycle of bacterial trigger factor (TF), using fluorescently labeled chaperone and ribosome-nascent chain complexes. Both the association and dissociation rates of TF-ribosome complexes are modulated by nascent chains, whereby their length, sequence, and folding status are influencing parameters. However, the effect of the folding status is modest, indicating that TF can bind small globular domains and accommodate them within its substrate binding cavity. In general, the presence of a nascent chain causes an up to 9-fold increase in the rate of TF association, which provides a kinetic explanation for the observed ability of TF to efficiently compete with other cytosolic chaperones for binding to nascent chains. Furthermore, a subset of longer nascent polypeptides promotes the stabilization of TF-ribosome complexes, which increases the half-life of these complexes from 15 to 50 s. Nascent chains thus regulate their folding environment generated by ribosome-associated chaperones.

Received for publication, October 5, 2007 , and in revised form, November 26, 2007.

^* This work was supported by Deutsche Forschungsgemeinschaft Grant SFB638 (to B. B. and E. D.), Human Frontier Science Programs (to E. D. and N. B.), a Heisenberg fellowship from the Deutsche Forschungsgemeinschaft (to E. D.), a fellowship from the Boehringer Ingelheim Fonds (to A. H.), and by a grant from the Fonds der Chemischen Industrie (to B. B.), by the Swiss National Science Fundation (SNSF), the National Center of Excellence in Research (NCER) Structured Biology program of the SNSF, and the ETH Research grant TH-3104-1 (to N. 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 Experimental Procedures, Figs. 1 and 2, Table 1, and additional references.

¹ To whom correspondence may be addressed. Tel.: 49-6221-546795; Fax: 49-6221-545894; E-mail: e.deuerling{at}zmbh.uni-heidelberg.de. ² To whom correspondence may be addressed. Tel.: 49-6221-546795; Fax: 49-6221-545894; E-mail: bukau{at}zmbh.uni-heidelberg.de.