Biosynthesis of vitamin B2 -: An essential zinc ion at the catalytic site of GTP cyclohydrolase II
Biosynthesis of vitamin B2 -: An essential zinc ion at the catalytic site of GTP cyclohydrolase II
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DOI：
10.1046/j.1432-1033.2002.03239.x
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发表时间：
2002-11-01
期刊：
影响因子：
--
通讯作者：
Bacher, A
中科院分区：
文献类型：
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作者：
Kaiser, J;Schramek, N;Bacher, A
GTP环水解酶II催化GTP分解释放甲酸盐和焦磷酸，生成2，5-二氨基-6-核糖氨基-4(~H)-嘧啶酮5‘-磷酸，这是核黄素生物合成的第一个中间体。该酶的每个亚基含有一个锌离子。用丝氨酸取代半胱氨酸残基54、65或67导致蛋白质无结合锌，不能从GTP的咪唑环或中间类似物2-氨基-5-甲酰氨基-6-核糖氨基-4(3H)-嘧啶酮5‘-三磷酸释放甲酸。然而，突变蛋白保留了从GTP和甲酰胺类中间类似物释放焦磷酸的能力。这些数据表明，该酶催化了一个有序反应，其中焦磷酸盐的水解性释放先于咪唑环的水解性攻击。开环和甲酸盐的释放都依赖于锌离子作为Lewis酸，它激活了参与两个碳-氮键顺序水解的两个水分子。
GTP cyclohydrolase II catalyzes the hydrolytic release of formate and pyrophosphate from GTP producing 2,5-diamino-6-ribosylamino-4(3H)-pyrimidinone 5'-phosphate, the first committed intermediate in the biosynthesis of riboflavin. The enzyme was shown to contain one zinc ion per subunit. Replacement of cysteine residue 54, 65 or 67 with serine resulted in proteins devoid of bound zinc and unable to release formate from the imidazole ring of GTP or from the intermediate analog, 2-amino-5-formylamino-6-ribosylamino- 4(3H)-pyrimidinone 5'-triphosphate. However, the mutant proteins retained the capacity to release pyrophosphate from GTP and from the formamide-type intermediate analog. The data suggest that the enzyme catalyzes an ordered reaction in which the hydrolytic release of pyrophosphate precedes the hydrolytic attack of the imidazole ring. Ring opening and formate release re both dependent on zinc ion acting as Lewis acid, which activates the two water molecules involved in the sequential hydrolysis of two carbon nitrogen bonds.