STRUCTURAL STUDIES ON ENZYMES INVOLVED IN SIALIC ACID TRANSFERASE, SULFUR ASSIMI

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目及 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者的研究机构。 1)一个系统涉及唾液酸转移酶，或将唾液酸添加到受体碳水化合物上的酶。唾液酸转移酶是催化含唾液酸的寡糖、多糖和糖缀合物合成的关键酶，这些寡糖、多糖和糖缀合物在原核生物和真核生物的许多生理和病理关键过程中起关键作用。尽管它们具有重要的生物学功能，但对这些酶的分子结构和催化机制知之甚少。本项目的长期目标是阐明ST的分子结构和催化机制，并开发ST抑制剂作为可用于治疗癌症和病原性细菌感染的有效治疗剂。2)实验室正在研究的另一种细胞途径是硫同化和硫酸盐活化途径。该实验室使用SSRL收集的数据确定了来自不同生物体的该途径中的许多酶结构。该提案将集中于更好地理解调节途径中的前两种酶以及随后参与含硫生物分子合成的酶的结构要求。3)最后，实验室最近启动的一个新项目是研究植物和光合细菌中参与生色团合成的酶的结构特征。特别是光敏色素的合成，它调节许多细胞对光的反应。PcyA是一种典型的铁氧还蛋白依赖性胆色素还原酶，参与形成藻蓝胆素（phycocyanobilin，PCB），PCB是感光细胞光敏色素和多种藻胆蛋白的发色团的前体。该PcyA酶通过四个电子还原胆绿素，并通过两个自由基中间体进行，这已被EPR光谱证实。我们已经产生了突变体，这些自由基的寿命延长到几个小时。晶体中已形成自由基酶，并经EPR证实。

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. 1) One system is involved in sialyltransferases, or enzymes that add sialic acid onto acceptor carbohydrates. Sialyltransferases are key enzymes that catalyze the synthesis of sialic acid-containing oligosaccharides, polysaccharides, and glycoconjugates that play pivotal roles in many physiologically and pathologically critical processes in both prokaryotic and eukaryotic organisms. Despite their important biological functions, little is known about the molecular architecture and catalytic mechanism of these enzymes. Our long-term goals of this project are to elucidate the molecular structure and catalytic mechanism of STs and to develop ST inhibitors as potent therapeutics that can be used to treat cancers and pathogenic bacterial infections. 2) Another cellular pathway the lab is investigating is in sulfur assimilation and the sulfate activation pathway. The lab has determined a number of enzyme structures in this pathway from diverse organisms using data collected at SSRL. This proposal will focus on better understanding the structural requirements for regulation of the first two enzymes in the pathway as well as subsequent enzymes involved in the synthesis of sulfur containing biomolecules. 3) Finally, a new project the lab has initiated recently is investigating the structural features on plant and photosynthetic bacteria enzymes involved in chromophore synthesis. In particular, synthesis of phytochromes that regulate many cellular processes in response to light. PcyA, a representative ferredoxin-dependent bilin reductase is responsible for the formation of phycocyanobilin (PCB), the precursor of the chromophores of the photoreceptor phytochrome and a number of phycobiliproteins. This PcyA enzyme reduces biliverdin by four electrons, and proceeds through two radical intermediates, which have been confirmed by EPR spectroscopy. We have generated mutants that extend the life time of these radicals to many hours. Radical enzyme has been formed in the crystal and confirmed by EPR.