Zhao Kehao, Chai Xiaomei, Marmorstein Ronen
The Wistar Institute, University of Pennsylvania, Philadelphia, PA 19104, USA.
Structure. 2003 Nov;11(11):1403-11. doi: 10.1016/j.str.2003.09.016.
Sir2 proteins are NAD(+)-dependant protein deactylases that have been implicated in playing roles in gene silencing, DNA repair, genome stability, longevity, metabolism, and cell physiology. To define the mechanism of Sir2 activity, we report the 1.5 A crystal structure of the yeast Hst2 (yHst2) Sir2 protein in ternary complex with 2'-O-acetyl ADP ribose and an acetylated histone H4 peptide. The structure captures both ligands meeting within an enclosed tunnel between the small and large domains of the catalytic protein core and permits the assignment of a detailed catalytic mechanism for the Sir2 proteins that is consistent with solution and enzymatic studies. Comparison of the ternary complex with the yHst2/NAD(+) complex, also reported here, and nascent yHst2 structure also reveals that NAD(+) binding accompanies intramolecular loop rearrangement for more stable NAD(+) and acetyl-lysine binding, and that acetyl-lysine peptide binding induces a trimer-monomer protein transition involving nonconserved Sir2 residues.
Sir2蛋白是依赖烟酰胺腺嘌呤二核苷酸（NAD(+)）的蛋白质去乙酰化酶，在基因沉默、DNA修复、基因组稳定性、寿命、新陈代谢和细胞生理学中发挥作用。为了确定Sir2活性的机制，我们报道了酵母Hst2（yHst2）Sir2蛋白与2'-O-乙酰基ADP核糖和乙酰化组蛋白H4肽形成的三元复合物的1.5埃晶体结构。该结构捕捉到了两种配体在催化蛋白核心的小结构域和大结构域之间的封闭通道内相遇的情况，并允许为Sir2蛋白指定一种详细的催化机制，这与溶液和酶学研究一致。本文还报道了三元复合物与yHst2/NAD(+)复合物以及新生yHst2结构的比较，结果表明NAD(+)结合伴随着分子内环重排，以实现更稳定的NAD(+)和乙酰赖氨酸结合，并且乙酰赖氨酸肽结合会诱导三聚体-单体蛋白转变，涉及非保守的Sir2残基。
