New Nickel Environment for Biology: Cofactor Assembly and Function

通过这个奖项，化学部生命过程化学项目资助了密歇根州立大学的Robert Hausinger博士和Jian Hu博士，研究微生物如何将乳酸的两个镜像结构相互转化，乳酸是碳水化合物代谢的核心元素。这种酶被称为乳酸外消旋酶，它需要蛋白质成分和镍。镍在生物学中很少被发现。更值得注意的是，乳酸外消旋酶中的镍存在于以前从未观察到的独特环境中。这个项目研究细菌是如何制造辅助因子来创造独特的环境的。这项工作为结构和生化机制领域的博士后研究员、研究生和本科生提供培训。这些研究人员还参与了与该主题相关的公众实践教育活动，这些活动将在大学的年度科学节上吸引所有年龄段的终身学习者。本研究阐明了乳酸消旋酶活性所需的四种蛋白的结构和功能方面。描述了LarB催化烟酸腺嘌呤二核苷酸吡啶环羧基化和磷酸酐键水解生成吡啶-3,5-二羧酸单核苷酸的新反应。对LarE（一种牺牲硫转移酶）的进一步研究，确定了两个羧基如何转化为硫代羧酸基，并确定了酶的脱氢丙氨酸侧链是否可以再生为半胱氨酸。这项工作揭示了LarC如何催化ctp依赖的Ni安装成吡啶-3-5-二硫代羧酸单核苷酸，这是环金属化反应的第一个生物例子，以产生辅助因子。最后，这些研究表明了辅因子是如何结合到不同的LarA物种上的，并确定了该酶催化的其他潜在转化。综上所述，这种新型含镍辅助因子的生物合成和作用可以被描述。这项创新的研究扩展了我们对镍生物化学的理解，并建立了一个涉及拴系镍钳辅助因子的氧化还原化学的新范例。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

With this award, the Chemistry of Life Processes Program in the Chemistry Division is funding Dr. Robert Hausinger and Dr. Jian Hu from Michigan State University to characterize how a microorganism interconverts the two mirror image structures of lactic acid, a central element of carbohydrate metabolism. The enzyme that does this, called lactate racemase, requires both a protein component and nickel. Nickel is very rarely found in biology. Even more remarkably, the nickel in lactate racemase is present in a unique environment never before observed. This project investigates how the bacterium makes the cofactor that creates the unique environment. This effort provides training to a postdoctoral researcher, a graduate student, and undergraduate students in the areas of structure and biochemical mechanisms. These researchers also participate in hands-on educational activities for the public related to this topic that will engage lifelong learners of all ages at the annual Science Festival at the university.This research elucidates structure-function aspects of the four proteins required for lactate racemase activity. It characterizes how LarB catalyzes a new reaction, carboxylation of the pyridinium ring of nicotinic acid adenine dinucleotide while hydrolyzing the phosphoanhydride linkage to produce pyridinium-3,5-dicarboxylic acid mononucleotide. Additional studies of LarE, a sacrificial sulfur transferase, establish how the two carboxylic acid groups are transformed into thiocarboxylate groups and define whether the resulting dehydroalanine side chain of the enzyme can be regenerated to cysteine. This work uncovers how LarC catalyzes the CTP-dependent installation of Ni into pyridinium-3-5-dithiocarboxylic acid mononucleotide, the first biological example of a cyclometallation reaction, to create the cofactor. Finally, these investigations show how the cofactor is bound to different LarA species and identifies other potential transformations catalyzed by the enzyme. In combination, the biosynthesis and roles of this novel nickel-containing cofactor can be described. This innovative research expands our understanding of nickel biochemistry and establishes a new paradigm for redox chemistry involving a tethered nickel-pincer cofactor.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.