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首页> 外文期刊>Journal of Molecular Biology >Structural insights into the substrate specificity of (S)-ureidoglycolate amidohydrolase and its comparison with allantoate amidohydrolase
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Structural insights into the substrate specificity of (S)-ureidoglycolate amidohydrolase and its comparison with allantoate amidohydrolase

机译：对氨基甲酸氨基水解酶的底物特异性的结构见解及其与丙二酸氨酸氨基水解酶的比较

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摘要

In plants, the ureide pathway is a metabolic route that converts the ring nitrogen atoms of purine into ammonia via sequential enzymatic reactions, playing an important role in nitrogen recovery. In the final step of the pathway, (S)-ureidoglycolate amidohydrolase (UAH) catalyzes the conversion of (S)-ureidoglycolate into glyoxylate and releases two molecules of ammonia as by-products. UAH is homologous in structure and sequence with allantoate amidohydrolase (AAH), an upstream enzyme in the pathway with a similar function as that of an amidase but with a different substrate. Both enzymes exhibit strict substrate specificity and catalyze reactions in a concerted manner, resulting in purine degradation. Here, we report three crystal structures of Arabidopsis thaliana UAH (bound with substrate, reaction intermediate, and product) and a structure of Escherichia coli AAH complexed with allantoate. Structural analyses of UAH revealed a distinct binding mode for each ligand in a bimetal reaction center with the active site in a closed conformation. The ligand directly participates in the coordination shell of two metal ions and is stabilized by the surrounding residues. In contrast, AAH, which exhibits a substrate-binding site similar to that of UAH, requires a larger active site due to the additional ureido group in allantoate. Structural analyses and mutagenesis revealed that both enzymes undergo an open-to-closed conformational transition in response to ligand binding and that the active-site size and the interaction environment in UAH and AAH are determinants of the substrate specificities of these two structurally homologous enzymes.
机译：在植物中，硫化物途径是通过顺序酶促反应将嘌呤的环氮原子转化为氨，在氮气回收中发挥重要作用。在该途径的最后步骤中， - 氨基甲酸二糖醇氨基水（UAH）催化 - 将（S）的转化为甲酸乙酯转化为乙醛酸盐并释放两种氨分子作为副产物。 UAH在结构和仲氨酸氨基水（AAH）中的结构和序列中是同源的，途径中的上游酶具有与酰胺酶类似的功能相似，但用不同的基材。两种酶以齐心的方式表现出严格的底物特异性和催化反应，导致嘌呤降解。在这里，我们报告了拟南芥uAh的三种晶体结构（与底物，反应中间体和产物结合），以及与丙二醇酸酯络合的大肠杆菌Aah的结构。 UAH的结构分析显示了双金属反应中心中的每个配体的不同结合模式，其具有闭合构象的活性位点。配体直接参与两个金属离子的配位壳，并通过周围的残留物稳定。相反，由于丙二醇酸盐中的另外的ureido基团，呈现出类似于UAH的底物结合位点的AAH，其需要较大的活性位点。结构分析和诱变显示，两种酶响应于配体结合而经历开孔的构象过渡，并且UAH和AAH中的有源位点尺寸和相互作用环境是这两种结构同源酶的底物特异性的决定因素。

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