Tungsten and Molybdenum Oxotransferases

单核钼或钨中心由一个或两个特殊的蝶呤衍生物的二硫代单位配位，称为钼蝶呤，末端氧/硫基和/或蛋白质侧链（丝氨酸，半胱氨酸或硒代半胱氨酸）构成30多种不同类型的氧转移酶的活性位点，这些酶涉及正式的氧原子向水或从水转移。普遍存在的钼酶参与碳、氮和硫的代谢，催化氧化还原电位超过800 mV的各种反应，而钨酶主要局限于嗜热厌氧菌，在羧酸和醛的水平上催化低电位转化。本研究的目的是探索这类酶的结构和机制多样性，特别强调钼酸盐和末端氧配体的作用以及决定钨或钼选择的因素。该方法是光谱学的，利用最近成功的利用共振拉曼探测活性位点结构和催化机制，通过氧和硫同位素标记实验，结合变温磁圆二色性和EPR来研究基态和激发态电子结构。在分子水平上详细了解金属酶的催化机制将最终导致酶和催化剂的改进，用于重要的生物和工业应用。除了生物技术意义之外，这类酶提供了一个独特的机会来探索一种新型金属酶活性位点是如何通过金属和配体环境的变化来响应进化的陆地变化和催化更广泛的氧转移酶反应的需要而进化的。

9808857 Johnson Mononuclear molybdenum or tungsten centers coordinated by the dithiolene units of one or two special pterin derivatives termed molybdopterin, terminal oxo/sulfido groups and/or protein side chains (serine, cysteine or selenocysteine) constitute the active sites of more than 30 distinct classes of oxotransferase enzymes involving formal oxygen atom transfer to or from water. The ubiquitous molybdoenzymes are involved in the metabolism of carbon, nitrogen and sulfur catalyzing a diverse range reactions spanning more than 800 mV in redox potential, whereas the tungstoenzymes are largely confined to thermophilic anaerobes in which they catalyze low potential conversions at the level of carboxylic acids and aldehydes. The objective of this research is to explore the structural and mechanistic diversity in this class of enzymes with particular emphasis on the role of the molybdopterin and terminal oxo ligands and the factors dictating the choice of tungsten or molybdenum. The approach is spectroscopic and exploits recent successes in using resonance Raman to probe the active site structures and catalytic mechanism via oxygen and sulfur isotopic labeling experiments and the combination of variable temperature magnetic circular dichroism and EPR to investigate ground and excited state electronic structure. Detailed understanding of the catalytic mechanisms of metallo-enzymes at the molecular level will ultimately lead to improved enzymes and catalysts for important biological and industrial applications. In addition to the biotechnological implications, this class of enzymes offer a unique opportunity to explore how a novel type of metalloenzyme active site has evolved via changes in the metal and ligand environment in response to evolutionary terrestrial changes and the need to catalyze a wider range of oxotransferase reactions.