Tungsten and Molybdenum Oxotransferases

9808857约翰逊单核钼或钨中心由一种或两种称为钼蝶呤的特殊蝶呤衍生物、末端氧/硫基和/或蛋白质侧链(丝氨酸、半胱氨酸或硒半胱氨酸)的二硫烯单元配位，构成了30多种不同类别的氧化转移酶的活性部位，这些酶涉及到水中的形式氧原子转移。普遍存在的钼酶参与碳、氮和硫的代谢，在氧化还原电位超过800 mV的范围内催化各种反应，而钨酶主要局限于嗜热厌氧菌，它们在羧酸和醛的水平上催化低电位转化。这项研究的目的是探索这类酶的结构和机制的多样性，特别是钼掺杂和末端氧配体的作用以及决定钨或钼的选择的因素。该方法是光谱方法，通过氧和硫同位素标记实验以及变温磁圆二色谱和电子顺磁共振相结合的方法研究基态和激发态电子结构，并利用共振拉曼光谱研究活性中心结构和催化机理。在分子水平上详细了解金属酶的催化机理将最终导致改进的酶和催化剂，用于重要的生物和工业应用。除了生物技术方面的影响，这类酶还提供了一个独特的机会来探索一种新型的金属酶活性部位是如何通过金属和配体环境的变化来进化的，以响应陆地进化的变化和催化更广泛的氧化转移酶反应的需要。

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.