Catalysis of the Cleavage of Uridine 3‘-2,2,2-Trichloroethylphosphate by a Designed Helix−Loop−Helix Motif Peptide
作者:Jesus Razkin、Helena Nilsson、Lars Baltzer
DOI:10.1021/ja075478i
日期:2007.11.28
catalyze the hydrolysis of phosphodiesters. The active site on the surface of the folded catalyst is composed of two histidine and four arginine residues, with the capacity to provide general acid, general base, and/or nucleophilic catalysis as well as transition state stabilization. Uridine 3'-2,2,2 trichloroethylphosphate (2) is a mimic of RNA with a leaving group pKa of 12.3. Its hydrolysis is energetically
折叠成螺旋-环-螺旋基序并二聚化形成四螺旋束的 42 个残基肽已被设计用于催化磷酸二酯的水解。折叠催化剂表面的活性位点由两个组氨酸和四个精氨酸残基组成,具有提供一般酸、一般碱和/或亲核催化以及过渡态稳定的能力。尿苷 3'-2,2,2 三氯乙基磷酸酯 (2) 是 RNA 的模拟物,离去基团 pKa 为 12.3。它的水解在能量上不如带有对硝基苯基离去基团的常用模型底物有利,因此是设计能够切割 RNA 的催化剂的更现实模型。多肽催化剂在 pH 7.0 下水解 2 的二级速率常数为 418 x 10(-6) M-1 s-1,咪唑催化反应的产物为 1.66 x 10(-6) M-1 s-1。pH 依赖性表明催化是由于残基的非质子化形式,pKa 约为 5.3,观察到的动力学溶剂同位素效应为 1.9,表明在过渡态存在显着的氢键,与一般酸碱催化一致. 速率常数比 k2(Pep)/k2(Im) 为 252