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。血红素在细胞中还发挥着许多其他重要的生化功能。有了这个奖项，化学部的生命过程化学项目资助佛罗里达州立大学的Elizabeth Stroupe博士研究一种特殊形式的血红素（称为siroheme）。Siroheme帮助利用微生物将环境中的硫或氮化合物化学转化为生物可用的形式。由于最近美国南部的洪水，商业养猪场产生的有毒硫副产品造成的环境污染已经成为一个问题，因此这个研究课题特别重要。Stroupe博士正在研究一种由两种细菌制成的关键酶（CysG），以确定siroheme形成的基础科学。通过了解西罗血红素是如何形成的，科学家们可以改进有毒硫化合物的生物修复。该项目培养不同群体的本科生和研究生进行分子结构测定，并跟踪酶在不同反应阶段的生化活性。Stroupe博士和她的学生们通过SCIGirls和佛罗里达州下一代科学标准推广项目，向初高中学生传授有机化学在生物学中所扮演的角色。变形杆菌利用单基因产物（CysG）合成血红素。CsyG是甲基转移酶（CysG-A）和双功能脱氢酶/铁螯合酶（CysG-B）基因融合事件的产物。CysG-B的双重功能及其作为钴螯合酶的替代功能的机制尚不清楚。其他生物体使用三种不同的酶来合成西罗血红素，包括CysG-B同源的SirC，这是一种单功能脱氢酶。应用x射线晶体学、生化分析和傅立叶变换离子回旋共振质谱（FT-ICR MS）来剖析西罗血红素合成最后两步的潜在机制。该项目解决的问题包括cyg - b中的双功能活性位点如何催化脱氢和金属螯合，以及螯合酶如何区分铁和钴来制造西罗血红素。研究人员还询问了当同源酶SirC仅作为脱氢酶时，cyg - b如何作为双功能脱氢酶/铁螯合酶发挥作用。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。

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.