Mechanisms of Iron-Sulfur Dependent Reactions

项目总结/摘要 甲基化反应在生物学中的普遍性和重要性已得到充分证实。甲基基团是 附加到广泛的生物分子，包括许多小分子代谢物和天然 产品和各种大分子，如蛋白质、DNA、RNA、碳水化合物和脂质。在广大 在大多数甲基化反应中，S-腺苷甲硫氨酸（SAM）是附加甲基的来源。在 在经典的甲基转移酶反应中，强亲核试剂如氧、氮和硫攻击sp3- 在极性SN 2反应中杂交SAM的甲基，得到S-腺苷高半胱氨酸作为副产物。 碳原子也可以通过这种机制甲基化，但只有当合适的亲核碳负离子可以被甲基化时， 生成的.相对最近，已经发现SAM可以用于甲基化惰性碳或 亚膦酸磷原子通过涉及自由基中间体的途径。这些非典型的SAM- 在抗生素、抗真菌剂、抗癌剂 和除草天然产物，并且仅由基团S-内的酶催化， 腺苷蛋氨酸超家族自由基SAM甲基化酶目前由三类（A类，B类， 和C类），基于结构体系结构、辅因子要求和作用机制。A类 酶使用Cys二联体催化sp2-杂交碳中心的甲基化。B类酶使用 钴胺素辅因子催化sp2-和sp3-杂化碳中心的甲基化。C类酶 使用两个同时结合的SAM分子来甲基化sp2杂化的碳中心。而且都要说明 附加的甲基衍生自SAM的第二分子。这项工作将继续努力， 了解这些自由基SAM甲基化酶如何工作，特别关注确定结构的努力 这些酶与底物、辅因子和中间体的结合。重要的系统包括RNA 涉及抗生素抗性的甲基酶，以及涉及生物合成的甲基酶 重要的抗生素，如硫链丝菌素A，那西肽和碳青霉烯类，目前最后的抗生素 度假村.

PROJECT SUMMARY/ABSTRACT The prevalence and significance of methylation reactions in biology is well established. Methyl groups are appended to a wide array of biological molecules, including numerous small-molecule metabolites and natural products, and various macromolecules, such as proteins, DNA, RNA, carbohydrates, and lipids. In the vast majority of methylation reactions, S-adenosylmethionine (SAM) is the source of the appended methyl group. In classical methyltransferase reactions, strong nucleophiles such as oxygen, nitrogen, and sulfur attack the sp3- hybridized methyl group of SAM in a polar SN2 reaction, affording S-adenosylhomocysteine as a co-product. Carbon atoms can also be methylated by this mechanism, but only if a suitably nucleophilic carbanion can be generated. Relatively recently, it has come to light that SAM can be used to methylate inert carbon or phosphinate phosphorous atoms via pathways involving radical intermediates. These noncanonical SAM- dependent methylations are found in numerous biosynthetic pathways for antibiotic, antifungal, anticancer, and herbicidal natural products, and are catalyzed exclusively by enzymes within the radical S- adenosylmethionine superfamily. Radical SAM methylases currently consist of three classes (Class A, Class B, and Class C) based on structural architecture, cofactor requirement, and mechanism of action. Class A enzymes use a Cys dyad to catalyze methylation of sp2-hybridized carbon centers. Class B enzymes use cobalamin cofactors to catalyze methylation of both sp2- and sp3-hybridized carbon centers. Class C enzymes use two simultaneously bound molecules of SAM to methylate sp2-hybridized carbon centers. In all cases, the appended methyl group derives from a second molecule of SAM. This work will continue our efforts to understand how these radical SAM methylases work, with a particular focus on efforts to determine structures of these enzymes with bound substrates, cofactors, and intermediates. Important systems include RNA methylases that are involved in antibiotic resistance, as well as methylases that are involved in the biosynthesis of important antibiotics, such as thiostrepton A, nosiheptide, and carbapenems, the antibiotics currently of last resort.