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J. Biol. Chem., Vol. 279, Issue 37, 38111-38117, September 10, 2004

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Identification of a Major Inter-ring Coupling Step in the GroEL Reaction Cycle^*

Daniel Poso, Anthony R. Clarke, and Steven G. Burston¶

From the Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, Bristol BS8 1TD, United Kingdom

It has been shown previously that the double-ring structure of GroEL can be converted to a single-ring species by site-directed amino acid replacements at the ring interface and that the resultant molecule retains many of the crucial chaperonin properties; it is structurally stable, hydrolytically active, and can bind both the co-chaperonin, GroES, and unfolded substrate proteins. By comparing the behavior of the double- and single-ring structures in response to nucleotide binding and hydrolysis, we elucidate steps in the ATP-driven reaction cycle at which there is conformational coupling between the rings. Remarkably, the parting of the rings has little effect either on the thermodynamic properties of ATP binding or on the ATP-induced conformational changes prior to hydrolysis. However, there is a marked effect on the rate-limiting process in the steady-state cycle; a step that is coincident with bond cleavage in ATP. The effect of the ring-ring interaction is to increase its activation enthalpy from 42.0 to 94.2 kJ/mol. These results show that the major conformational coupling step, where structural rearrangements in one ring are propagated to the other, is the slowest process the ATPase cycle of GroEL.

Received for publication, February 17, 2004 , and in revised form, May 5, 2004.

^* 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 by a Wellcome Trust program grant.

^¶ Supported by a Wellcome Trust project grant.

Supported by the EPSRC and a full scholarship from the Biochemistry Department of the University of Bristol. To whom correspondence should be addressed. E-mail: d.poso{at}bristol.ac.uk or s.g.burston{at}bristol.ac.uk.

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