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J. Biol. Chem., Vol. 279, Issue 16, 15723-15727, April 16, 2004

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Trigonal DnaK-DnaJ Complex Versus Free DnaK and DnaJ

HEAT STRESS CONVERTS THE FORMER TO THE LATTER, AND ONLY THE LATTER CAN DO DISAGGREGATION IN COOPERATION WITH ClpB^*

Yo-hei Watanabe and Masasuke Yoshida

From the Chemical Resources Laboratory, R-1, Tokyo Institute of Technology, Nagatsuta 4259, Yokohama 226-8503, Japan

DnaK from Thermus thermophilus (TDnaK) is unique because significant fractions of cellular TDnaK exist as a trigonal K·J complex that consists of three copies each of TDnaK, TDnaJ, and an assembly factor TDafA. Here, chaperone functions of the K·J complex and free TDnaK plus free TDnaJ (K+J) were compared. Substrate proteins were completely denatured at 72–73 °C or 89 °C in the absence or the presence of K·J complex or K+J and were subsequently incubated at a moderate temperature of 55 °C. TGrpE and ATP were always included in the K·J complex and K+J, and TClpB was supplemented at 55 °C. At 72–73 °C, both the K·J complex and K+J suppressed heat aggregation of substrate proteins. During the next incubation at 55 °C, K+J, assisted by TClpB, was able to disaggregate the heat aggregates and efficiently reactivate activities of the proteins, whereas the K·J complex was not; it reactivated only the soluble inactivated proteins. When substrate proteins were heated to 89 °C, both the K·J complex and K+J were no longer able to prevent heat aggregation, and because of selective, irreversible denaturation of TDafA the K·J complex dissociated into K+J, which then exhibited disaggregation activity during the next incubation at 55 °C. Thus, TClpB-assisted disaggregation activity belongs only to K+J, and TDafA is a potential thermosensor for converting the K·J complex to K+J in response to heat stress.

Received for publication, August 8, 2003 , and in revised form, January 13, 2004.

^* This work was supported by Grant-in-aid for Scientific Research on Priority Area No. 14037217 (to M. Y.) 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.

Supported in part by a research fellowship of the Japan Society for the Promotion of Science for Young Scientists.

To whom correspondence should be addressed. Fax: 81-45-924-5277; E-mail: myoshida{at}res.titech.ac.jp.

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