Crystal structure of CobK reveals strand-swapping between Rossmann-fold domains and molecular basis of the reduced precorrin product trap.
Crystal structure of CobK reveals strand-swapping between Rossmann-fold domains and molecular basis of the reduced precorrin product trap.
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DOI：
10.1038/srep16943
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发表时间：
2015-11-30
影响因子：
4.6
通讯作者：
Pickersgill RW
中科院分区：
文献类型：
--
作者：
Gu S;Sushko O;Deery E;Warren MJ;Pickersgill RW
CoBK催化钴胺生物合成途径中前角质环的基本还原。CobK的晶体结构表明，尽管没有特征序列，但该酶包含两个Rossmann折叠结构域，分别与辅酶和底物结合。两个平行的β-折叠交换了它们的最后一条β-链，得到了一种新颖的片状拓扑，这是罗斯曼折叠的一个有趣的变体。捕获的辅酶和产物的三元络合物显示了五个保守的碱性残基，它们紧密地锚定着产物的四个吡咯的羧基。脱辅酶和全酶结构中的环状结构都无序地包围着产物，进一步加强了结合。该结构与C18质子化和前角蛋白-6A的前R氢化物从NADPH转移到C19的机理相一致，揭示了CobK的特异性所依赖的相互作用。还原的前角蛋白产物几乎完全被埋葬，这表明了一种非凡的代谢物通道，生物合成途径中的下一种酶触发了产物的释放。
CobK catalyzes the essential reduction of the precorrin ring in the cobalamin biosynthetic pathway. The crystal structure of CobK reveals that the enzyme, despite not having the signature sequence, comprises two Rossmann fold domains which bind coenzyme and substrate respectively. The two parallel β-sheets have swapped their last β-strands giving a novel sheet topology which is an interesting variation on the Rossmann-fold. The trapped ternary complex with coenzyme and product reveals five conserved basic residues that bind the carboxylates of the tetrapyrrole tightly anchoring the product. A loop, disordered in both the apoenzyme and holoenzyme structures, closes around the product further tightening binding. The structure is consistent with a mechanism involving protonation of C18 and pro-R hydride transfer from NADPH to C19 of precorrin-6A and reveals the interactions responsible for the specificity of CobK. The almost complete burial of the reduced precorrin product suggests a remarkable form of metabolite channeling where the next enzyme in the biosynthetic pathway triggers product release.