Biosynthesis of Colitose: Expression, Purification, and Mechanistic Characterization of GDP-4-keto-6-deoxy-<scp>d</scp>-mannose-3-Dehydrase (ColD) and GDP-<scp>l</scp>-colitose Synthase (ColC)
作者:Jenefer Alam、Noelle Beyer、Hung-wen Liu
DOI:10.1021/bi0483763
日期:2004.12.1
itself. Our studies also established ColC as GDP-L-colitose synthase, which is a bifunctional enzyme catalyzing the C-5 epimerization of GDP-4-keto-3,6-dideoxy-D-mannose and the subsequent C-4 keto reduction of the resulting L-epimer to give GDP-L-colitose. Reported herein are the detailed accounts of the overexpression, purification, and characterization of ColD and ColC. Our studies show that their
L-Colitose是在革兰氏阴性脂多糖的O-抗原中发现的3,6-二脱氧己糖。为了研究这种不寻常糖的生物合成,我们已经克隆并测序了假单胞菌耶尔森氏菌VI的L-colitose生物合成基因簇。此簇中的colD和colC基因已过表达,每种基因产物均已纯化和鉴定。我们的结果表明,ColD作为GDP-4-酮-6-脱氧-D-甘露糖-3-脱水酶,负责GDP-4-酮-6-脱氧-D-甘露糖的C-3脱氧。此酶是辅酶B(6)依赖的,其催化作用是通过氨基转移步骤开始的,其中吡ido醛5'-磷酸酯(PLP)在L-谷氨酸的前体中转化为吡ido胺5'-磷酸酯(PMP)。该辅酶与酮糖底物形成席夫碱,所得的加合物经历PMP介导的β脱水反应,生成糖烯胺中间体,互变异构化和水解后释放出氨,生成GDP-4-酮基3,6-双脱氧-D-甘露糖为产物。结合的氨基转移-脱氧活性将ColD本身置于一类中。我们的研究还将ColC确立为GDP