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J. Biol. Chem., Vol. 281, Issue 31, 21813-21819, August 4, 2006

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Co-translational Binding of GroEL to Nascent Polypeptides Is Followed by Post-translational Encapsulation by GroES to Mediate Protein Folding^*

Bei-Wen Ying, Hideki Taguchi¹, and Takuya Ueda²

From the Department of Medical Genome Sciences, Graduate School of Frontier Sciences, The University of Tokyo, FSB-401, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562 and the Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency, 4-1-8 Honcho Kawaguchi, Saitama, 332-0012, Japan

The eubacterial chaperonins GroEL and GroES are essential chaperones and primarily assist protein folding in the cell. Although the molecular mechanism of the GroEL system has been examined previously, the mechanism by which GroEL and GroES assist folding of nascent polypeptides during translation is still poorly understood. We previously demonstrated a co-translational involvement of the Escherichia coli GroEL in folding of newly synthesized polypeptides using a reconstituted cell-free translation system (Ying, B. W., Taguchi, H., Kondo, M., and Ueda, T. (2005) J. Biol. Chem. 280, 12035–12040). Employing the same system here, we further characterized the mechanism by which GroEL assists folding of translated proteins via encapsulation into the GroEL-GroES cavity. The stable co-translational association between GroEL and the newly synthesized polypeptide is dependent on the length of the nascent chain. Furthermore, GroES is capable of interacting with the GroEL-nascent peptide-ribosome complex, and experiments using a single-ring variant of GroEL clearly indicate that GroES association occurs only at the trans-ring, not the cis-ring, of GroEL. GroEL holds the nascent chain on the ribosome in a polypeptide length-dependent manner and post-translationally encapsulates the polypeptide using the GroES cap to accomplish the chaperonin-mediated folding process.

Received for publication, March 31, 2006 , and in revised form, May 22, 2006.

^* This work was supported by Grants-in aid for Scientific Research on Priority Area 14037217 (to T. U.) and 17049009 (to H. T.) from the Ministry of Education, Science, Sports and Culture of Japan. 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 may be addressed. Tel./Fax: 81-4-7136-3644; E-mail: taguchi{at}k.u-tokyo.ac.jp. ² To whom correspondence may be addressed. Tel.: 81-4-7136-3641; Fax: 81-4-7136-3642; E-mail: ueda{at}k.u-tokyo.ac.jp.

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