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。 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。唾液酸基转移酶是催化合成含唾液酸寡糖、多糖和糖共轭化合物的关键酶，在原核生物和真核生物的许多生理和病理过程中发挥着关键作用。尽管它们具有重要的生物学功能，但人们对它们的分子结构和催化机理知之甚少。我们这个项目的长期目标是阐明STS的分子结构和催化机制，并开发ST抑制剂作为有效的治疗药物，可用于治疗癌症和致病菌感染。2)实验室正在研究的另一条细胞途径是硫同化和硫酸盐活化途径。该实验室利用SSRL收集的数据，从不同的生物体中确定了这一途径中的一些酶结构。这项建议将侧重于更好地理解该途径中前两种酶以及参与合成含硫生物分子的后续酶的结构要求。3)最后，实验室最近启动的一个新项目是研究参与生色团合成的植物和光合细菌酶的结构特征。特别是，光敏色素的合成，它调节许多细胞对光的反应过程。PcyA是一种具有代表性的铁氧还蛋白依赖的胆碱还原酶，它负责藻蓝胆蛋白(PCB)的形成，而PCB是光感受器光敏色素发色团的前体和许多藻胆蛋白。这种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，EPR光谱证实了这一点。我们已经产生了突变体，可以将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.