Crystal structure of the free radical intermediate of pyruvate:ferredoxin oxidoreductase.
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 A-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.
Chabrière
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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.
Vernède
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Guigliarelli
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Charon
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Hatchikian
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Fontecilla-Camps
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D000105:Acetyl Coenzyme A / Q000378:metabolism; D000693:Anaerobiosis; D001665:Binding Sites; D002245:Carbon Dioxide / Q000378:metabolism; D002384:Catalysis; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003067:Coenzymes / Q000737:chemistry* / Q000378:metabolism; D003460:Crystallization; D018360:Crystallography, X-Ray; D003901:Desulfovibrio / Q000201:enzymology*; D019281:Dimerization; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals / Q000737:chemistry / Q000378:metabolism; D007658:Ketone Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D008968:Molecular Conformation; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011487:Protein Conformation; D050743:Pyruvate Synthase; D019289:Pyruvic Acid / Q000378:metabolism; D013835:Thiamine Pyrophosphate / Q000737:chemistry* / Q000378:metabolism
D003067:Coenzymes; D005609:Free Radicals; D002245:Carbon Dioxide; D000105:Acetyl Coenzyme A; D019289:Pyruvic Acid; D007658:Ketone Oxidoreductases; D050743:Pyruvate Synthase; D013835:Thiamine Pyrophosphate