Protein-Cofactor Interactions and EPR Parameters for the QH Quinone Binding Site of Quinol Oxidase. A Density Functional Study
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- 作者：Sylwia Kacprzak ; Martin Kaupp ; and Fraser MacMillan
- 刊名：Journal of the American Chemical Society
- 出版年：2006
- 出版时间：May 3, 2006
- 年：2006
- 卷：128
- 期：17
- 页码：5659 - 5671
- 全文大小：276K
- 年卷期：v.128,no.17(May 3, 2006)
- ISSN：1520-5126
文摘
Recent multifrequency EPR studies of the "high-affinity" quinone binding site of quinol oxidase(QH site) have suggested a very asymmetric hydrogen-bonding environment for the semiquinone radicalanion state. Single-sided hydrogen bonding to the O1 carbonyl position was one of the proposals, whichcontrasts with some previous experimental indications. Here density functional calculations of the EPRparameters (g-tensors, 13C, 1H, and 17O hyperfine tensors) for a wide variety of supermolecular modelcomplexes have been used to provide insight into the detailed relations among structure, environment,and EPR parameters of ubisemiquinone radical anions. A single-sided binding model is not able to accountfor the experimentally observed low gx component of the g-tensor or for the observed magnitude of theasymmetry of the 13C carbonyl HFC tensors. Based on the detailed comparison between computation andexperiment, a model with two hydrogen bonds to O1 and one hydrogen bond to O4 is suggested for the QHsite, but a model with one more hydrogen bond on each side cannot be excluded. Several generalconclusions on the interrelations between EPR parameters and hydrogen bond patterns of ubisemiquinonesin proteins are provided.