The structure of 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline decarboxylase provides insights into the mechanism of uric acid degradation
The structure of 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline decarboxylase provides insights into the mechanism of uric acid degradation
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DOI：
10.1074/jbc.m701297200
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发表时间：
2007-06-22
影响因子：
4.8
通讯作者：
Zanotti, Giuseppe
中科院分区：
文献类型：
--
作者：
Cendron, Laura;Berni, Rodolfo;Zanotti, Giuseppe
尿酸完全降解为（S）-尿囊素，如最近阐明的，涉及三个酶促反应。在类人猿进化过程中，该途径的基因被假基因化而失活，导致血液中高浓度的尿酸盐和痛风易感性。在这里，我们描述了同二聚体2-氧代-4-羟基-4-羧基-5-脲基咪唑啉脱羧酶的1.8埃分辨率晶体结构，该酶催化尿酸盐降解途径的最后一步，对于无配体酶和与底物类似物（R）-尿囊素和鸟嘌呤复合的酶。每个单体包含10个α-螺旋，分为两个结构域，并组装在一个新的折叠。活性位点的结构和突变分析使我们能够确定一些对催化至关重要的残基，其中His-67和Glu-87似乎起着特别重要的作用。Glu-87可促进羧酸根基团的退出，因为静电排斥使底物的基态不稳定，而His-67可能参与质子化步骤，导致作为反应产物的（S）-尿囊素对映体的立体选择性形成。2-氧代-4-羟基-4-羧基-5-脲基咪唑啉脱羧酶的结构和功能特性可以提供有用的信息，鉴于这种酶在痛风的酶促治疗中的潜在用途。
The complete degradation of uric acid to (S)-allantoin, as recently elucidated, involves three enzymatic reactions. Inactivation by pseudogenization of the genes of the pathway occurred during hominoid evolution, resulting in a high concentration of urate in the blood and susceptibility to gout. Here, we describe the 1.8 angstrom resolution crystal structure of the homodimeric 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline decarboxylase, which catalyzes the last step in the urate degradation pathway, for both ligand-free enzyme and enzyme in complex with the substrate analogs (R)-allantoin and guanine. Each monomer comprises ten alpha-helices, grouped into two domains and assembled in a novel fold. The structure and the mutational analysis of the active site have allowed us to identify some residues that are essential for catalysis, among which His-67 and Glu-87 appear to play a particularly significant role. Glu-87 may facilitate the exit of the carboxylate group because of electrostatic repulsion that destabilizes the ground state of the substrate, whereas His-67 is likely to be involved in a protonation step leading to the stereoselective formation of the (S)-allantoin enantiomer as reaction product. The structural and functional characterization of 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline decarboxylase can provide useful information in view of the potential use of this enzyme in the enzymatic therapy of gout.