CD and MCD of CytC3 and Taurine Dioxygenase: Role of the Facial Triad in -KG-Dependent Oxygenases

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• 作者：Michael L. Neidig ; Christina D. Brown ; Kenneth M. Light ; Danica Galoni Fujimori ; Elizabeth M. Nolan ; John C. Price ; Eric W. Barr ; J. Martin Bollinger ; Jr. ; Carsten Krebs ; Christopher T. Walsh ; Edward I
• 刊名：Journal of the American Chemical Society
• 出版年：2007
• 出版时间：November 21, 2007
• 年：2007
• 卷：129
• 期：46
• 页码：14224 - 14231
• 全文大小：223K
• 年卷期：v.129,no.46(November 21, 2007)
• ISSN：1520-5126

文摘

The -ketoglutarate (-KG)-dependent oxygenases are a large and diverse class of mononuclearnon-heme iron enzymes that require Fe^II, -KG, and dioxygen for catalysis with the -KG cosubstratesupplying the additional reducing equivalents for oxygen activation. While these systems exhibit a diversearray of reactivities (i.e., hydroxylation, desaturation, ring closure, etc.), they all share a common structuralmotif at the Fe^II active site, termed the 2-His-1-carboxylate facial triad. Recently, a new subclass of -KG-dependent oxygenases has been identified that exhibits novel reactivity, the oxidative halogenation ofunactivated carbon centers. These enzymes are also structurally unique in that they do not contain thestandard facial triad, as a Cl^- ligand is coordinated in place of the carboxylate. An Fe^II methodology involvingCD, MCD, and VTVH MCD spectroscopies was applied to CytC3 to elucidate the active-site structuraleffects of this perturbation of the coordination sphere. A significant decrease in the affinity of Fe^II for apo-CytC3 was observed, supporting the necessity of the facial triad for iron coordination to form the restingsite. In addition, interesting differences observed in the Fe^II/-KG complex relative to the cognate complexin other -KG-dependent oxygenases indicate the presence of a distorted 6C site with a weak water ligand.Combined with parallel studies of taurine dioxygenase and past studies of clavaminate synthase, theseresults define a role of the carboxylate ligand of the facial triad in stabilizing water coordination via aH-bonding interaction between the noncoordinating oxygen of the carboxylate and the coordinated water.These studies provide initial insight into the active-site features that favor chlorination by CytC3 over thehydroxylation reactions occurring in related enzymes.