Examining the role of phosphate in glycosyl transfer reactions of Cellulomonas uda cellobiose phosphorylase using d-glucal as donor substrate
作者:Patricia Wildberger、Lothar Brecker、Bernd Nidetzky
DOI:10.1016/j.carres.2012.04.003
日期:2012.7
becomes protonated from below its six-membered ring through stereoselective re side attack at C-2. The proposed catalytic mechanism, which is supported by results of docking studies, involves direct protonation of D-glucal by the enzyme-bound phosphate, which then performs nucleophilic attack on the reactive C-1 of donor substrate. When offered D-glucose next to D-glucal and phosphate, CuCPase produces
已显示来自纤维单胞菌的纤维二糖磷酸化酶(CuCPase)利用D-葡萄糖作为缓慢的供体底物,用于立体定向糖基转移至无机磷酸盐,得到2-脱氧-α-D-葡萄糖1-磷酸作为产物。当在D(2)O中进行时,D-葡萄糖的酶促磷酸水解会在C-2的赤道位置掺入氘,这意味着立体化学反应过程,其中底物通过立体选择性的侧面进攻从其六元环下方质子化在C-2。拟议的催化机制得到对接研究结果的支持,涉及通过酶结合的磷酸盐直接使D-葡萄糖质子化,然后对供体底物的反应性C-1进行亲核攻击。如果在D-葡萄糖和磷酸盐旁边提供D-葡萄糖,CuCPase产生2-脱氧-β-D-葡萄糖基-(1→4)-D-葡萄糖和2-脱氧-α-D-葡萄糖1-磷酸的比例受存在的两个受体底物的质量作用支配。催化浓度的磷酸盐可有效促进2-脱氧-β-D-葡萄糖基-(1→4)-D-葡萄糖的酶促合成,表明催化反应通过CuCPase,D-葡萄糖,磷酸盐和D-葡萄糖。