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J. Biol. Chem., Vol. 280, Issue 48, 39852-39859, December 2, 2005

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Cyc2p, a Membrane-bound Flavoprotein Involved in the Maturation of Mitochondrial c-Type Cytochromes^*

Delphine G. Bernard, Sophie Quevillon-Cheruel¶, Sabeeha Merchant, Bernard Guiard1, and Patrice P. Hamel2

From the Department of Chemistry and Biochemistry, UCLA, Los Angeles, California 90095-1569, Centre de Génétique Moléculaire, CNRS, 91198 Gif-sur-Yvette, France and ^¶Institut de Biochimie et de Biophysique Moléculaire et Cellulaire, Université Paris-Sud, Orsay 91405, France

Mitochondrial apocytochrome c and c₁ are converted to their holoforms in the intermembrane space by attachment of heme to the cysteines of the CXXCH motif through the activity of assembly factors cytochrome c heme lyase and cytochrome c₁ heme lyase (CCHL and CC₁HL). The maintenance of apocytochrome sulfhydryls and heme substrates in a reduced state is critical for the ligation of heme. Factors that control the redox chemistry of the heme attachment reaction to apocytochrome c are known in bacteria and plastids but not in mitochondria. We have explored the function of Cyc2p, a candidate redox cytochrome c assembly component in yeast mitochondria. We show that Cyc2p is required for the activity of CCHL toward apocytochrome c and c₁ and becomes essential for the heme attachment to apocytochrome c₁ carrying a CAPCH instead of CAACH heme binding site. A redox function for Cyc2p in the heme lyase reaction is suggested from 1) the presence of a noncovalently bound FAD molecule in the C-terminal domain of Cyc2p, 2) the localization of Cyc2p in the inner membrane with the FAD binding domain exposed to the intermembrane space, and 3) the ability of recombinant Cyc2p to carry the NADPH-dependent reduction of ferricyanide. We postulate that, in vivo, Cyc2p interacts with CCHL and is involved in the reduction of heme prior to its ligation to apocytochrome c by CCHL.

Received for publication, August 4, 2005 , and in revised form, September 29, 2005.

^* The project was supported by the National Research Initiative of the United States Department of Agriculture Cooperative State Research, Education and Extension Service, Grant 2004-35318-14953 (to S. M.), Muscular Dystrophy Association Grant 3618 (to P. P. H.), and a Ministère de l'Education Nationale, de la Recherche et de la Technologie Fellowship (to D. G. B.). 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.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. 1 and 2.

¹ To whom correspondence may be addressed: Centre de Génétique Moléculaire, CNRS, Ave. de la Terrasse, 91198 Gif-sur-Yvette, France. Tel.: 33-1-69-82-31-84; Fax: 33-1-69-82-31-50; E-mail: guiard{at}cgm.cnrs-gif.fr. ² To whom correspondence may be addressed: Plant Cellular and Molecular Biology, 500 Aronoff Laboratory, 318 W. 12th Ave., The Ohio State University, Columbus, OH 43210. Tel.: 614-292-3817; Fax: 614-292-6345; E-mail: hamel.16{at}osu.edu.

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