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J. Biol. Chem., Vol. 283, Issue 30, 20857-20863, July 25, 2008

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The Type III Secretion Chaperone SycE Promotes a Localized Disorder-to-Order Transition in the Natively Unfolded Effector YopE^*

Loren Rodgers, Alicia Gamez, Roland Riek^¶||, and Partho Ghosh¹

From the Section of Molecular Biology and the Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, the ^¶Salk Institute for Biological Studies, La Jolla, California 92037, and the ^||Laboratory of Physical Chemistry, Eidgenössische Technische Hochschule Zürich, CH-8093 Zürich, Switzerland

Many virulence-related, bacterial effector proteins are translocated directly into the cytosol of host cells by the type III secretion (TTS) system. Translocation of most TTS effectors requires binding by specific chaperones in the bacterial cytosol, although how chaperones promote translocation is unclear. To provide insight into the action of such chaperones, we studied the consequences of binding by the Yersinia chaperone SycE to the effector YopE by NMR. These studies examined the intact form of the effector, whereas prior studies have been limited to well ordered fragments. We found that YopE had the characteristics of a natively unfolded protein, with its N-terminal 100 residues, including its chaperone-binding (Cb) region, flexible and disordered in the absence of SycE. SycE binding caused a pronounced disorder-to-order transition in the Cb region of YopE. The effect of SycE was strictly localized to the Cb region, with other portions of YopE being unperturbed. These results provide stringent limits on models of chaperone action and are consistent with the chaperone promoting formation of a three-dimensional targeting signal in the Cb region of the effector. The target of this putative signal is unknown but appears to be a bacterial component other than the TTS ATPase YscN.

Received for publication, March 25, 2008 , and in revised form, May 5, 2008.

^* This work was supported, in whole or in part, by National Institutes of Health Grants T32 GM007240 (to L. R.) and R01 AI061452 (to P. G.). This work was also supported by grants from the Universitywide AIDS Research Program (to L. R.) and the National Science Foundation Bridges to the Doctorate Program (to A. G.). 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 Fig. S1.

¹ To whom correspondence should be addressed: Dept. of Chemistry & Biochemistry 0375, 9500 Gilman Dr., University of California, San Diego, La Jolla, CA 92093-0375. Fax: 858-822-2871; E-mail: pghosh{at}ucsd.edu.

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