Unité de Bioénergétique et Ingénierie des Protéines, UMR 7281, Centre National de la Recherche Scientifique, Institut de Microbiologie de la Méditerranée, and Aix-Marseille University, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France.
Inorg Chem. 2012 Mar 19;51(6):3409-19. doi: 10.1021/ic201533p. Epub 2012 Mar 7.
The periplasmic nitrate reductase NAP belongs to the DMSO reductase family that regroups molybdoenzymes housing a bis-molybdopterin cofactor as the active site. Several forms of the Mo(V) state, an intermediate redox state in the catalytic cycle of the enzyme, have been evidenced by EPR spectroscopy under various conditions, but their structure and catalytic relevance are not fully understood. On the basis of structural data available from the literature, we built several models that reproduce the first coordination sphere of the molybdenum cofactor and used DFT methods to make magneto-structural correlations on EPR-detected species. "High-g" states, which are the most abundant Mo(V) species, are characterized by a low-anisotropy g tensor and a high g(min) value. We assign this signature to a six-sulfur coordination sphere in a pseudotrigonal prismatic geometry with a partial disulfide bond. The "very high-g" species is well described with a sulfido ion as the sixth ligand. The "low-g" signal can be successfully associated to a Mo(V) sulfite-oxidase-type active site with only one pterin moiety coordinated to the molybdenum ion with an oxo or sulfido axial ligand. For all these species we investigate their catalytic activity using a thermodynamic point of view on the molybdenum coordination sphere. Beyond the periplasmic nitrate reductase case, this work provides useful magneto-structural correlations to characterize EPR-detected species in mononuclear molybdoenzymes.
周质硝酸盐还原酶 NAP 属于 DMSO 还原酶家族，该家族包含钼酶，其活性位点为双钼喋呤辅因子。通过各种条件下的 EPR 光谱，已经证明了该酶催化循环中的中间氧化还原状态 Mo(V) 存在几种形式，但它们的结构和催化相关性尚未完全理解。基于文献中可用的结构数据，我们构建了几个模型，这些模型再现了钼辅因子的第一配位层，并使用 DFT 方法对 EPR 检测到的物种进行磁结构相关性研究。“高 g”态是最丰富的 Mo(V) 物种，其特征是各向异性 g 张量低和 g(min) 值高。我们将此特征分配给具有部分二硫键的拟三角棱柱几何形状的六硫配位层。“非常高 g”物种可以很好地用硫离子作为第六配体来描述。“低 g”信号可以成功地与 Mo(V)亚硫酸盐氧化酶型活性位点相关联，该活性位点只有一个蝶呤部分与钼离子配位，具有一个轴向配体为氧或硫。对于所有这些物种，我们从钼配位层的热力学角度研究了它们的催化活性。除了周质硝酸盐还原酶的情况外，这项工作还提供了有用的磁结构相关性，以表征单核钼酶中 EPR 检测到的物种。
