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J. Biol. Chem., Vol. 281, Issue 12, 8169-8174, March 24, 2006

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Self-association and Chaperone Activity of Hsp27 Are Thermally Activated^*

From the Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada

The small heat shock protein 27 (Hsp27) is an oligomeric, molecular chaperone in vitro. This chaperone activity and other physiological roles attributed to Hsp27 have been reported to depend on the state of self-association. In the present work, we have used sedimentation velocity experiments to demonstrate that the self-association of Hsp27 is independent of pH and ionic strength but increases significantly as the temperature is increased from 10 to 40 °C. The largest oligomers formed at 10 °C are 8-12 mer, whereas at 40 °C oligomers as large as 22-30 mer are observed. Similarly, the chaperone activity of Hsp27 as indicated by its ability to inhibit dithiothreitol-induced insulin aggregation also increases with increased temperature, with a particularly sharp increase in activity as temperature is increased from 34 to 43 °C. Similar studies of an Hsp27 triple variant that mimics the behavior of the phosphorylated protein establish that this protein has greatly diminished chaperone activity that responds minimally to increased temperature. We conclude that Hsp27 can exploit a large number of oligomerization states and that the range of oligomer size and the magnitude of chaperone activity increase significantly as temperature is increased over the range that is relevant to the physiological heat shock response.

Received for publication, November 23, 2005 , and in revised form, January 23, 2006.

^* This work was supported in part by Canadian Institutes of Health Research Operating Grant MCP-14021 (to A. G. M.), a University graduate fellowship and a Cordula and Günter Paetzold fellowship (to B. L.-G.), and a Canada Research Chair (to A. G. M.). 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 should be addressed: Dept. of Biochemistry and Molecular Biology, Life Sciences Centre, 2350 Health Sciences Mall, University of British Columbia, Vancouver, B.C. V6T 1Z3, Canada. Tel.: 604-822-3719; Fax: 604-822-6860; E-mail: mauk{at}interchange.ubc.ca.

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