MECHANISMS OF ME-TRANSFER AND ACETYL-COA SYNTHESIS

产甲烷细菌是人类肠道菌群的重要组成部分，它们的存在和/或不存在已被证明具有明显的流行病学。因此，对产甲烷菌代谢途径的了解对人类健康具有意想不到的意义。这项建议的目的是阐明参与产甲烷菌基本甲基转移反应的多亚单位复合体的结构。其中较大的复合体，乙酰辅酶A脱羧酶合成酶(ACDS)，介导了醋酸酯的C-C键断裂。该复合体分为三个不同的组分，每个组分催化三个反应之一：可逆乙酰辅酶A转移酶活性、CO：CO2氧化还原酶活性和甲基转移酶活性。长期目标是确定这些组分中每一个的结构，以便深入了解它们的催化机理。一旦获得了所有这些结构，它们将被用来组装ACDS复合体的完整图景，这可以作为了解不同组分之间底物转移机制的框架。第二个目标是从甲胺中确定参与甲基营养生长的蛋白质的结构。在这里，主要的焦点不仅是阐明甲基转移酶及其同源皮质激素蛋白的结构，而且还了解甲基是如何与皮质激素因子相互转移的。由于这些皮质中枢在生物学中无处不在，这样的见解将对许多生物系统具有普遍意义。

Methanogenic bacteria form an important part of the human intestinal flora where their presence and/or absence has been shown to have a distinct epidemiology. Hence the understanding of the metabolic pathways of methanogenes has unexpected relevance to human health. The objective of this proposal is to elucidate the structures of multi- subunit complexes that participate in fundamental methyl transfer reactions in methanogens. The larger of these complexes, the acetyl-CoA decarbonylase synthase (ACDS), mediates the C-C bond cleavage of acetate. This complex is compartmentalized into three discrete components, each of which catalyzes one of three reactions: reversible acetyl-CoA transferase activity, CO:CO2 oxidoreductase activity, and methyltransferase activity. The long-term goal is to determine the structures of each of these components in order to gain insight into their catalytic mechanisms. Once all of these structures are obtained, they will be utilized to assemble a complete picture of the ACDS complex that can serve as a framework for understanding the mechanisms of substrate transfer between the different components. The second target is directed at the structural determination of proteins involved in methylotrophic growth from methylamines. Here too the major focus is not only in elucidating the structures of a methyl transferase and its cognate corrinoid protein, but also to understand how a methyl group is transferred to and from a corrinoid factor. As these corrinoid centers are ubiquitous in biology, such insights will be of general relevance to many biological systems.