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 （Sir2）酶家族在从一些细菌到人类的生物中是保守的。它们参与了许多细胞过程，如DNA双链断裂的修复、非同源末端连接、染色体稳定、衰老和基因沉默。增加SIR2基因的剂量可以延长酵母和秀丽隐杆线虫的寿命。本提案的重点是确定底物特异性和Sir2家族酶的催化机制。由于这些酶存在于许多生物体中，并且它们似乎位于细胞的不同区域，因此每种酶都可能具有独特的底物。这些酶的真正底物还没有很好地确定。Sir2及其同系物sirtuins的酶促功能是最近才确定的。研究表明sirtuins是NAD+依赖的去乙酰化酶，它催化了一种独特的反应，将NAD+分解和底物去乙酰化紧密结合在一起，形成一种新的化合物o -acetyl- 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（未发表的数据）。sirtuins是如何实现这种独特的机制并产生一种新的化合物的，目前还不清楚。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 We have recently shown that O-acetyl-ADP-ribose itself has a biological roles (unpublished data).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.