Insights into the Catalytic Mechanism of dTDP-Glucose4,6-Dehydratase from Quantum Mechanics/Molecula

• 作 者: 马广才 刘永军
• 机 构: 山东大学理论化学研究所,济南,山东 250100
• 出 处: 第十二届全国量子化学会议
• 发表日期: 2014年1期

　　dTDP-Glucose 4,6-dehydratase catalyzes the biotransformation of dTDP-glucose into dTDP-4-keto-6-deoxy-glucose.We have utilized the quantum mechanical/molecular mechanical(QM/MM)approach to investigate the reaction mechanism of dTDP-glucose 4,6-dehydratase from Streptomyces venezuelae.On the basis of our calculation results,the previously proposed mechanism has been revised.It is demonstrated that the overall catalytic cycle can be divided into three distinct chemical steps: oxidation,dehydration and reduction,containing four enzymatic elementary reactions,and one non-enzymatic enol-ketotautomerization reaction.The oxidation step proceeds through a concerted asynchronous mechanism with a calculated barrier of 20.7 kcal/mol,in which the hydride transfer lags behind the proton transfer.The dehydration step prefers to a stepwise mechanism rather than a concerted mechanism,which involves an enolate intermediate.Two highly conserved residues Glu129 and Asp128 are involved in this step.In the reduction step,the NADH returns the hydride back to glycosyl C6 and the phenolic hydroxyl of Tyr151 spontaneously denotes proton to C4-keto group,forming an enol sugar as enzymatic product.After dissociating from the dehydratase active site and diffusing into the solution,this enol sugar will facilely rearrange to give the more favorable dTDP-4-keto-6-dexoyglucose product.Although the Thr127 is not directly involved in the whole enzymatic reaction,it may be responsible for promoting the catalysis by forming hydrogen-bonding interactions with glycosyl.These calculation results have provided a new understanding of the catalytic mechanism of dTDP-glucose 4,6-dehydratase,even though it is different from the previously experimental proposals.