Henriksson Lena M, Björkelid Christofer, Mowbray Sherry L, Unge Torsten
Department of Cell and Molecular Biology, Uppsala University, Biomedical Center, Box 596, SE-751 24 Uppsala, Sweden.
Acta Crystallogr D Biol Crystallogr. 2006 Jul;62(Pt 7):807-13. doi: 10.1107/S0907444906019196. Epub 2006 Jun 20.
1-deoxy-D-xylulose 5-phosphate reductoisomerase catalyzes the NADPH-dependent rearrangement and reduction of 1-deoxy-D-xylulose 5-phosphate to form 2-C-methyl-D-erythritol 4-phosphate, as the second step of the deoxyxylulose 5-phosphate/methylerythritol 4-phosphate pathway found in many bacteria and plants. The end product, isopentenyl diphosphate, is the precursor of various isoprenoids vital to all living organisms. The pathway is not found in humans; the mevalonate pathway is instead used for the formation of isopentenyl diphosphate. This difference, combined with its essentiality, makes the reductoisomerase an excellent drug target in a number of pathogenic organisms. The structure of 1-deoxy-D-xylulose 5-phosphate reductoisomerase from Mycobacterium tuberculosis (Rv2870c) was solved by molecular replacement and refined to a resolution of 1.9 A. The enzyme exhibited an estimated kcat of 5.3 s-1 and Km and kcat/Km values of 7.2 microM and 7.4x10(5) M-1 s-1 for NADPH and 340 microM and 1.6x10(4) M-1 s-1 for 1-deoxy-D-xylulose 5-phosphate. In the structure, a sulfate is bound at the expected site of the phosphate moiety of the sugar substrate. The M. tuberculosis enzyme displays a similar fold to the previously published structures from Escherichia coli and Zymomonas mobilis. Comparisons offer suggestions for the design of specific drugs. Furthermore, the new structure represents an intermediate conformation between the open apo form and the closed holo form observed previously, giving insights into the conformational changes associated with catalysis.
1-脱氧-D-木酮糖5-磷酸还原异构酶催化1-脱氧-D-木酮糖5-磷酸的NADPH依赖性重排和还原反应，生成2-C-甲基-D-赤藓糖醇4-磷酸，这是许多细菌和植物中发现的脱氧木酮糖5-磷酸/甲基赤藓糖醇4-磷酸途径的第二步。终产物异戊烯基二磷酸是对所有生物体都至关重要的各种类异戊二烯的前体。该途径在人类中不存在；相反，甲羟戊酸途径用于异戊烯基二磷酸的形成。这种差异，再加上其必要性，使得还原异构酶成为许多致病生物中一个极好的药物靶点。通过分子置换解析了结核分枝杆菌（Rv2870c）的1-脱氧-D-木酮糖5-磷酸还原异构酶的结构，并将其精修至1.9埃的分辨率。该酶对NADPH的估计催化常数kcat为5.3 s-1，米氏常数Km和催化效率kcat/Km值分别为7.2 microM和7.4×10(5) M-1 s-1，对1-脱氧-D-木酮糖5-磷酸的Km和kcat/Km值分别为340 microM和1.6×10(4) M-1 s-1。在该结构中，一个硫酸根结合在糖底物磷酸部分的预期位置。结核分枝杆菌的这种酶与先前发表的大肠杆菌和运动发酵单胞菌的结构具有相似的折叠方式。比较结果为特定药物的设计提供了建议。此外，新结构代表了之前观察到的开放无辅基形式和封闭全酶形式之间的中间构象，为与催化作用相关的构象变化提供了深入了解。
