Avalos José L, Bever Katherine M, Wolberger Cynthia
Howard Hughes Medical Institute, Department of Biophysics and Biophysical Chemistry, School of Medicine, Johns Hopkins University, 725 N. Wolfe Street, Baltimore, Maryland 21205, USA.
Mol Cell. 2005 Mar 18;17(6):855-68. doi: 10.1016/j.molcel.2005.02.022.
Sir2 enzymes form a unique class of NAD(+)-dependent deacetylases required for diverse biological processes, including transcriptional silencing, regulation of apoptosis, fat mobilization, and lifespan regulation. Sir2 activity is regulated by nicotinamide, a noncompetitive inhibitor that promotes a base-exchange reaction at the expense of deacetylation. To elucidate the mechanism of nicotinamide inhibition, we determined ternary complex structures of Sir2 enzymes containing nicotinamide. The structures show that free nicotinamide binds in a conserved pocket that participates in NAD(+) binding and catalysis. Based on our structures, we engineered a mutant that deacetylates peptides by using nicotinic acid adenine dinucleotide (NAAD) as a cosubstrate and is inhibited by nicotinic acid. The characteristics of the altered specificity enzyme establish that Sir2 enzymes contain a single site that participates in catalysis and nicotinamide regulation and provides additional insights into the Sir2 catalytic mechanism.
Sir2 酶构成了一类独特的依赖烟酰胺腺嘌呤二核苷酸（NAD⁺）的脱乙酰酶，参与多种生物学过程，包括转录沉默、细胞凋亡调控、脂肪动员和寿命调节。Sir2 活性受烟酰胺调节，烟酰胺是一种非竞争性抑制剂，它通过碱基交换反应抑制脱乙酰作用。为阐明烟酰胺抑制的机制，我们测定了含有烟酰胺的 Sir2 酶的三元复合物结构。这些结构表明，游离烟酰胺结合在一个保守口袋中，该口袋参与 NAD⁺ 的结合和催化。基于我们得到的结构，我们设计了一种突变体，该突变体使用烟酸腺嘌呤二核苷酸（NAAD）作为共底物对肽进行脱乙酰化，并受烟酸抑制。这种特异性改变的酶的特性表明，Sir2 酶含有一个参与催化和烟酰胺调节的单一位点，并为 Sir2 催化机制提供了更多见解。
