GLUTAMINE DEPENDENT NAD+ SYNTHETASE FROM MYCOBACTERIUM TUBERCULOSIS

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 底物通道的定义是代谢产物从一个活性部位转移到另一个活性部位，而不需要在溶剂中进行交换。尽管在某些情况下底物通道存在争议，而且远未解决，但实验证明它参与了谷氨酰胺转移酶(GAT)超家族中普遍存在的多结构域酶的催化反应。这些酶催化蛋白质、氨基酸、辅因子、嘌呤和嘧啶生物合成中的关键代谢反应，所有这些生物合成都有一个共同点，即谷氨酰胺在谷氨酰胺酶活性部位水解为谷氨酸和氨。产生的氨通过结构域之间的隧道(氨隧道)转移到受体结构域(合成酶或合成酶结构域)的第二个活性部位。NAD+合成酶代表了GAT超家族中一个未发现和未被描述的类别。它催化依赖于ATP的烟酸腺嘌呤二核苷酸(NaAD+)转化为NAD+，这是NAD+从头合成的最后一步。NAD+历来被认为是参与还原-氧化反应的酶的辅因子。NAD+的一个新出现的重要作用是作为参与细胞信号传递、细胞分裂、细胞寿命和免疫反应的分子的来源。在人类中，NAD+是通过从头合成或从吡啶核苷酸循环途径获得的，而在结核分枝杆菌中，NAD+的产生完全依赖于从头合成途径。该项目的主要目标是在蛋白质中建立催化和局部动力学之间的联系，并表征NAD+合成酶中区域间信号转导和氨转移的机制。这个项目将有助于底物通道和酶催化的基础知识。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Substrate channeling is defined as the transfer of a metabolite from an active site to another without exchanging in the solvent. Although in several cases substrate channeling is controversial and far from being settled, it has been experimentally implicated in the reactions catalyzed by the ubiquitous multidomain enzymes of the glutamine amidotransferase (GAT) superfamily. These enzymes catalyze key metabolic reactions in protein, amino acid, cofactor, purine and pyrimidine biosyntheses, all of which have in common the hydrolysis of glutamine to glutamate and ammonia in the glutaminase active site. The ammonia produced is transfered through an inter-domain tunnel (the ammonia tunnel) to a second active site in the acceptor domain (a synthase or synthetase domain). NAD+ synthetase represents an unprecented and uncharacterized class of the GAT superfamily. It catalyzes the ATP-dependent transformation of nicotinic acid adenine dinucleotide (NaAD+) to NAD+ , the last step of the de novo biosynthesis of NAD+. NAD+ is historically known as the cofactor of enzymes involved in reduction-oxidation reactions. An emerging and important role for NAD+ is as source of molecules involved in cell signaling, cell division, cell longevity and immune response. While in humans NAD+ is obtained either from de novo biosynthesis or from the pyridine nucleotide recycling pathways, in M. tuberculosis NAD+ production relies entirely on the de novo biosynthetic pathway. The main goal of this project is to establish a link between catalysis and local dynamics in the protein and to characterize the mechanisms of interdomain signaling and of ammonia transfer in NAD+ synthetase. This project will contribute to the basic knowledge of substrate channeling and enzyme catalysis.