Mechanism of Sir2 Family of NAD+-dependent Deacetylases

描述（由申请人提供）：沉默信息调节因子2（Sir 2）酶家族在从一些细菌到人类的生物体中是保守的。它们参与了许多细胞过程，如通过非同源末端连接修复DNA双链断裂、染色体稳定性、衰老和基因沉默。增加SIR 2基因的剂量可以促进酵母和C.优雅该提案的重点是确定底物特异性和Sir 2家族酶的催化机制。因为这些酶存在于许多生物体中，并且因为它们似乎位于细胞的不同区域，所以每种酶都有可能具有独特的底物。这些酶的真实底物尚未完全确定。Sir 2及其同系物（称为sirtuins）的酶功能最近才被确定。研究表明，sirtuins是NAD+依赖性的脱乙酰酶，催化一种独特的反应，该反应将NAD+分解和底物脱乙酰化紧密结合，形成一种新的化合物O-乙酰基-ADP-核糖。我们最近发现O-乙酰基-ADP-核糖本身具有生物学作用（未发表数据）。sirtuins如何执行这样一个独特的机制，并产生一个新的化合物仍然是未知的。在这个提议中，底物特异性和催化机制的细节将被确定。

DESCRIPTION (provided by applicant): The silent information regulator 2 (Sir2) family of enzymes is conserved in organisms ranging from some bacteria to human. They have been implicated in many cellular processes such as the repair of DNA doublestrand breaks through nonhomologous end-joining, chromosome stability, aging, and gene silencing. Increased dosage of SIR2 genes promoted increased lifespan in yeast and C. elegans. The focus of this proposal is to determine the substrate specificity and the mechanism of catalysis by the Sir2 family of enzymes. Because these enzymes are present in many organisms and because they appear to be localized in different areas in the cell, it is possible that each has unique substrates. The authentic substrates for these enzymes have not been well established. The enzymatic function of Sir2 and its homologs, called sirtuins, were established just recently. It was demonstrated that sirtuins are NAD+-dependent deacetylases, catalyzing a unique reaction, which tightly couples NAD+ breakdown and substrate deacetylation to the formation of a novel compound, O-acetyl-ADP-ribose. We have recently shown that O-acetyl-ADP-ribose itself has a biological roles (unpublished data). How sirtuins carry out such a unique mechanism and produce a novel compound is still unknown. In this proposal, substrate specificity and the details of the catalytic mechanism will be determined.