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Science 21 December 2001:
Vol. 294. no. 5551, pp. 2559 - 2563
DOI: 10.1126/science.1066198
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Reports

Crystal Structure of the Free Radical Intermediate of Pyruvate:Ferredoxin Oxidoreductase

Eric Chabrière,13 Xavier Vernède,1 Bruno Guigliarelli,2 Marie-Hélène Charon,1 E. Claude Hatchikian,2 Juan C. Fontecilla-Camps1*

In anaerobic organisms, the decarboxylation of pyruvate, a crucial component of intermediary metabolism, is catalyzed by the metalloenzyme pyruvate: ferredoxin oxidoreductase (PFOR) resulting in the generation of low potential electrons and the subsequent acetylation of coenzyme A (CoA). PFOR is the only enzyme for which a stable acetyl thiamine diphosphate (ThDP)-based free radical reaction intermediate has been identified. The 1.87 Å-resolution structure of the radical form of PFOR from Desulfovibrio africanus shows that, despite currently accepted ideas, the thiazole ring of the ThDP cofactor is markedly bent, indicating a drastic reduction of its aromaticity. In addition, the bond connecting the acetyl group to ThDP is unusually long, probably of the one-electron type already described for several cation radicals but not yet found in a biological system. Taken together, our data, along with evidence from the literature, suggest that acetyl-CoA synthesis by PFOR proceeds via a condensation mechanism involving acetyl (PFOR-based) and thiyl (CoA-based) radicals.

1 Laboratoire de Cristallographie et Cristallogenèse des Protéines, Institut de Biologie Structurale Jean-Pierre Ebel, Commissariat à l'Energie Atomique, Université Joseph Fourier, CNRS, 41, rue Jules Horowitz, 38027 Grenoble Cedex 1, France.
2 Unité de Bioenérgetique et Ingénerie des Protéines, Institut de Biologie Structurale et Microbiologie, CNRS, 31, chemin J. Aiguier, 13402 Marseilles, France.
3 Laboratoire de Cristallographie et Modélisation des Matériaux Minéraux et Biologiques, Unité Mixte de Recherche 7036 CNRS, Université Henri Poincaré, Nancy 1B.P. 239, 54506 Vandoeuvre-les-Nancy, France.
*   To whom correspondence should be addressed. E-mail: juan{at}lccp.ibs.fr

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