University of Chinese Academy of Sciences, Beijing, 100049, China; Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, 300308, China.
Institute of Biological Chemistry, Academia Sinica, Taipei, 11529, Taiwan.
Biochem Biophys Res Commun. 2020 Jan 1;521(1):31-36. doi: 10.1016/j.bbrc.2019.10.035. Epub 2019 Oct 23.
The epimerase MoeE5 from Streptomyces viridosporus converts UDP-glucuronic acid (UDP-GlcA) to UDP-galacturonic acid (UDP-GalA) to provide the first sugar in synthesizing moenomycin, a potent inhibitor against bacterial peptidoglycan glycosyltransferases. The enzyme belongs to the UDP-hexose 4-epimerase family, and uses NAD as its cofactor. Here we present the complex crystal structures of MoeE5/NAD/UDP-GlcA and MoeE5/NAD/UDP-glucose, determined at 1.48 Å and 1.66 Å resolution. The cofactor NAD is bound to the N-terminal Rossmann-fold domain and the substrate is bound to the smaller C-terminal domain. In both crystals the C4 atom of the sugar moiety of the substrate is in close proximity to the C4 atom of the nicotinamide of NAD, and the O4 atom of the sugar is also hydrogen bonded to the side chain of Tyr154, suggesting a productive binding mode. As the first complex structure of this protein family with a bound UDP-GlcA in the active site, it shows an extensive hydrogen-bond network between the enzyme and the substrate. We further built a model with the product UDP-GalA, and found that the unique Arg192 of MoeE5 might play an important role in the catalytic pathway. Consequently, MoeE5 is likely a specific epimerase for UDP-GlcA to UDP-GalA conversion, rather than a promiscuous enzyme as some other family members.
来自变红红链霉菌的差向异构酶 MoeE5 将 UDP-葡萄糖醛酸 (UDP-GlcA) 转化为 UDP-半乳糖醛酸 (UDP-GalA)，为莫能菌素的合成提供了第一个糖基，莫能菌素是一种针对细菌肽聚糖糖基转移酶的强效抑制剂。该酶属于 UDP-己糖 4-差向异构酶家族，以 NAD 为辅因子。我们在此介绍了 MoeE5/NAD/UDP-GlcA 和 MoeE5/NAD/UDP-葡萄糖复合物的晶体结构，其分辨率分别为 1.48Å 和 1.66Å。辅因子 NAD 与 N 端 Rossmann 折叠结构域结合，底物与较小的 C 端结构域结合。在这两个晶体中，底物糖部分的 C4 原子与 NAD 中烟酰胺的 C4 原子非常接近，并且糖的 O4 原子也与 Tyr154 的侧链形成氢键，表明结合方式具有产性。作为该蛋白家族与活性位点结合的第一个 UDP-GlcA 复合物结构，它显示了酶与底物之间广泛的氢键网络。我们进一步构建了含有产物 UDP-GalA 的模型，并发现 MoeE5 的独特 Arg192 可能在催化途径中发挥重要作用。因此，MoeE5 可能是 UDP-GlcA 到 UDP-GalA 转化的特异性差向异构酶，而不是其他一些家族成员那样的混杂酶。
