Structural analysis of the siroheme biosynthetic enzyme CysG, a central player in sulfur metabolism

血红素是一种含铁分子，允许血红蛋白在血液中携带氧气。血红素还在细胞中发挥着许多其他重要的生化功能。有了这个奖项，化学系的生命过程化学项目将资助佛罗里达州立大学的伊丽莎白·斯特鲁普博士研究一种特殊形式的血红素(称为西罗亚铁血红素)。Siroheme使用微生物帮助将环境中的硫或氮化合物化学转化为生物可用的形式。这一研究课题特别重要，因为由于美国南部最近发生洪灾，商业养猪场产生的有毒硫磺副产品造成的环境污染已经成为问题。斯特劳普博士正在研究一种由两种细菌组成的关键酶(CysG)，以确定形成西罗西莫的基础科学。通过了解西罗铁血红素是如何形成的，科学家可能会改进有毒硫化物的生物修复。该项目对不同的本科生和研究生进行了分子结构测定方面的培训，并跟踪了酶在反应的不同阶段的生化活性。斯特劳普博士和她的学生们通过SciGirls和佛罗里达州的下一代科学标准推广计划向初中生和高中生传授对有机化学在生物学中所起作用的赞赏。变形杆菌使用单基因产物(CysG)来合成铁血红素。CsyG是甲基转移酶(CysG-A)和双功能脱氢/铁络合酶(CysG-B)基因融合的产物。CysG-B的双功能及其作为钴络合酶的替代功能的机制尚不清楚。其他生物使用三种不同的酶来合成铁血红素，包括CysG-B同系物SIRC，这是一种单功能脱氢酶。用X射线结晶学、生化分析和傅立叶变换离子回旋共振质谱仪(FT-ICR-MS)分析了合成四氢铁血红素后两步反应的机理。本项目涉及的问题包括CysG-B中的双功能活性中心如何催化脱氢和金属螯合，以及螯合酶如何区分铁和钴来生成铁铁血红素。研究人员还询问，当SIRC，一种同源酶，只起脱氢作用时，CysG-B如何起到双功能脱氢酶/铁络合酶的作用。这一奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Heme is the iron-containing molecule that allows hemoglobin to carry oxygen in blood. Heme also plays many other important biochemical functions in cells. With this award, the Chemistry of Life Processes Program in the Chemistry Division is funding Dr. Elizabeth Stroupe at Florida State University to study a special form of heme (called siroheme). Siroheme helps chemically transform environmental sulfur or nitrogen compounds to biologically usable forms using microbes. This research topic is of particular importance because environmental pollution in the form of toxic sulfur byproducts from commercial pig farms has become problematic due to recent flooding in the southern United States. Dr. Stroupe is studying a key enzyme (CysG) made from two bacteria in order to determine the basic science of siroheme formation. By knowing how siroheme is formed, scientists may improve upon the bio-remediation of toxic sulfur compounds. The project trains diverse groups of undergraduate and graduate students in molecular structure determinations and follows the biochemical activity of enzymes at various stages of reaction. Dr. Stroupe and her students impart an appreciation for the role that organic chemistry plays in biology to middle and high school students through the SCIGirls and Florida's Next Generation Science Standards outreach programs.Proteobacteria use a single gene product (CysG) to synthesize siroheme. CsyG is the product of a gene fusion event between a methyltransferase (CysG-A) and a bifunctional dehydrogenase/ferrochelatase (CysG-B). The mechanisms for CysG-B's bifunctionality and its alternative function as a cobaltchelatase are unknown. Other organisms use three distinct enzymes for siroheme synthesis, including the CysG-B homolog SirC, which is a monofunctional dehydrogenase. X-ray crystallography, biochemical analysis, and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) are applied to dissect the underlying mechanisms for the last two steps of siroheme synthesis. The questions addressed by this project include how bifunctional active sites in CysG-B catalyze dehydrogenation and metal chelation and how chelatase discriminates between iron and cobalt to make siroheme. Researchers also ask how CysG-B functions as a bifunctional dehydogenase/ferrochelatase when SirC, a homologous enzyme, only functions as a dehydrogenase.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.