Radical SAM Enzymes: Molecular Mechanisms of Radical Initiation

自由基SAM是已知的最大的酶超家族之一，其成员催化 在生活的各个领域的反应都有显著的多样性。自由基SAM酶参与了 必需辅因子和抗生素的合成、DNA损伤的修复和复合体的组装 生物金属簇合物，以及许多其他反应。人体内存在自由基SAM酶 以及在有益微生物和致病微生物中的作用，对理解它们的 基本属性和机制。拟议的研究将促进对 自由基SAM机制，尤其是这种大分子中所有酶所共有的自由基引发过程 和多样化的超级大家庭。研究工作将集中在使用快速冷冻捕获激进中间体- 淬火、低温还原、退火和光解方法。然后，这些中间体将被 利用电子顺磁共振和电子自旋共振等光谱学方法来表征的 核双共振，以及X射线结晶学等结构方法。计算型 研究将提供对稳定性/反应性和反应途径的见解。大部分工作都将建立 关于最近发现的一种新的有机金属中间体，该中间体含有铁与铁之间的直接键 铁-硫簇的结构和腺苷部分的碳，这种结构使人想起辅酶B12。 这些结果将提供对生物学中这种基本和普遍存在的反应的理解，以及它的 令人惊讶的是有机金属化学的介入。

Radical SAM is one of the largest enzyme superfamilies known, with its members catalyzing a remarkable diversity of reactions in all domains of life. Radical SAM enzymes are involved in the synthesis of essential cofactors and antibiotics, repair of DNA damage, and the assembly of complex biological metal clusters, among many other reactions. The presence of radical SAM enzymes in humans as well as in both beneficial and pathogenic microbes lends high significance to understanding their fundamental properties and mechanisms. The proposed research will develop a critical understanding of radical SAM mechanisms, in particular the radical initiation process common to all enzymes in this large and diverse superfamily. Research efforts will focus on trapping radical intermediates using rapid freeze- quench, cryoreduction, annealing, and photolysis approaches. These intermediates will then be characterized by using spectroscopic approaches such as electron paramagnetic resonance and electron- nuclear double resonance, and structural approaches such as X-ray crystallography. Computational studies will provide insights into stability/reactivity and reaction pathways. Much of the work will build on the recent discovery of a novel organometallic intermediate containing a direct bond between an iron of the iron-sulfur cluster and a carbon of an adenosyl moiety, a structure reminiscent of coenzyme B12. The results will provide an understanding of this fundamental and ubiquitous reaction in biology, and its surprising involvement of organometallic chemistry.