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首页> 外文OA文献 >D-ribose-5-phosphate isomerase B from Escherichia coli is also a functional D-allose-6-phosphate isomerase, while the Mycobacterium tuberculosis enzyme is not
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D-ribose-5-phosphate isomerase B from Escherichia coli is also a functional D-allose-6-phosphate isomerase, while the Mycobacterium tuberculosis enzyme is not

机译：大肠杆菌的D-核糖5-磷酸异构酶B也是一种功能性D-阿洛糖6-磷酸异构酶，而结核分枝杆菌酶不是

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Interconversion of D-ribose-5-phosphate (R5P) and D-ribulose-5-phosphate is an important step in the pentose phosphate pathway. Two unrelated enzymes with R5P isomerase activity were first identified in Escherichia coli, RpiA and RpiB. In this organism, the essential 5-carbon sugars were thought to be processed by RpiA, while the primary role of RpiB was suggested to instead be interconversion of the rare 6-carbon sugars D-allose-6-phosphate (All6P) and D-allulose-6-phosphate. In Mycobacterium tuberculosis, where only an RpiB is found, the 5-carbon sugars are believed to be the enzyme's primary substrates. Here, we present kinetic studies examining the All6P isomerase activity of the RpiBs from these two organisms and show that only the E. coli enzyme can catalyze the reaction efficiently. All6P instead acts as an inhibitor of the M. tuberculosis enzyme in its action on R5P. X-ray studies of the M. tuberculosis enzyme co-crystallized with All6P and 5-deoxy-5-phospho-D-ribonohydroxamate (an inhibitor designed to mimic the 6-carbon sugar) and comparison with the E. coli enzyme's structure allowed us to identify differences in the active sites that explain the kinetic results. Two other structures, that of a mutant E. coli RpiB in which histidine 99 was changed to asparagine and that of wild-type M. tuberculosis enzyme, both co-crystallized with the substrate ribose-5-phosphate, shed additional light on the reaction mechanism of RpiBs generally.
机译：D-核糖-5-磷酸酯（R5P）和D-核糖-5-磷酸酯的相互转化是戊糖磷酸途径中的重要步骤。首先在大肠杆菌中鉴定出两种具有R5P异构酶活性的不相关酶，即RpiA和RpiB。在这种生物中，必需的5碳糖被认为是RpiA加工的，而RpiB的主要作用则是将稀有的6碳糖D-阿洛糖6-磷酸（All6P）和D- 6-磷酸阿洛糖。在仅发现RpiB的结核分枝杆菌中，认为5碳糖是该酶的主要底物。在这里，我们目前进行动力学研究，检查来自这两种生物的RpiBs的All6P异构酶活性，并显示只有大肠杆菌酶才能有效地催化反应。相反，All6P在其对R5P的作用中充当结核分枝杆菌酶的抑制剂。与All6P和5-deoxy-5-phospho-D-ribonohydroxamate（设计用来模拟6碳糖的抑制剂）共结晶的结核分枝杆菌酶的X射线研究以及与大肠杆菌酶结构的比较使我们以确定解释动力学结果的活性位点的差异。其他两个结构，即突变的大肠杆菌RpiB的结构（其中组氨酸99变为天冬酰胺）和野生型结核分枝杆菌的结构，都与5核糖核糖共结晶，这为反应提供了更多的亮点。 RpiB的一般机制。

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