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J. Biol. Chem., Vol. 279, Issue 43, 44621-44627, October 22, 2004

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The Chloroplast Rieske Iron-Sulfur Protein

AT THE CROSSROAD OF ELECTRON TRANSPORT AND SIGNAL TRANSDUCTION^*

Catherine de Vitry, Yexin Ouyang¶, Giovanni Finazzi, Francis-André Wollman, and Toivo Kallas¶

From the Physiologie Membranaire et Moléculaire du Chloroplaste CNRS UPR 1261, Institut de Biologie Physico-Chimique, 13 Rue Pierre et Marie Curie, 75005 Paris, France and ^¶Department of Biology and Microbiology, University of Wisconsin, Oshkosh, Wisconsin 54901

We have addressed the functional and structural roles of three domains of the chloroplast Rieske iron-sulfur protein; that is, the flexible hinge that connects the transmembrane helix to the soluble cluster-bearing domain, the N-terminal stromal protruding domain, and the transmembrane helix. To this aim mutants were generated in the green alga Chlamydomonas reinhardtii. Their capacities to assemble the cytochrome b f complex, perform plastoquinol oxidation, and signal ⁶redox-induced activation of the light-harvesting complex II kinase during state transition were tested in vivo. Deletion of one residue and extensions of up to five residues in the flexible hinge had no significant effect on complex accumulation or electron transfer efficiency. Deletion of three residues (3G) dramatically decreased reaction rates by a factor of 10. These data indicate that the chloroplast iron-sulfur protein-linking domain is much more flexible than that of its counterpart in mitochondria. Despite greatly slowed catalysis in the 3G mutant, there was no apparent delay in light-harvesting complex II kinase activation or state transitions. This indicates that conformational changes occurring in the Rieske protein did not represent a limiting step for kinase activation within the time scale tested. No phenotype could be associated with mutations in the N-terminal stromal-exposed domain. In contrast, the N17V mutation in the Rieske protein transmembrane helix resulted in a large decrease in the cytochrome f synthesis rate. This reveals that the Rieske protein transmembrane helix plays an active role in assembly-mediated control of cytochrome f synthesis. We propose a structural model to interpret this phenomenon based on the C. reinhardtii cytochrome b₆f structure.

Received for publication, June 22, 2004 , and in revised form, August 5, 2004.

^* This work was supported by the CNRS, National Science Foundation Grant MCB 0091415, and University of Wisconsin-Oshkosh Faculty Development R788 grants (to T. K.). 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.

To whom correspondence should be addressed. Tel.: 33-1-58-41-50-55; Fax: 33-1-58-41-50-22; E-mail: catherine.devitry{at}ibpc.fr.

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