Glutamine binding opens the ammonia channel and activates glucosamine-6P synthase
Glutamine binding opens the ammonia channel and activates glucosamine-6P synthase
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DOI：
10.1074/jbc.m511689200
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发表时间：
2006-02-17
影响因子：
4.8
通讯作者：
Golinelli-Pimpaneau, B
中科院分区：
文献类型：
--
作者：
Mouilleron, S;Badet-Denisot, MA;Golinelli-Pimpaneau, B
葡糖胺-6 β合酶催化果糖-6 β和谷氨酰胺合成葡糖胺-6 β，并使用通道将氨从其转氨酶转移到其合酶活性位点。葡糖胺-6P合酶的X射线结构已经在果糖-6P存在下以2.05埃分辨率测定，并且在果糖-6P和6-重氮-5-氧代-L-正亮氨酸存在下以2.35埃分辨率测定，6-重氮-5-氧代-L-正亮氨酸是共价修饰N-末端催化半胱氨酸的谷氨酰胺亲和类似物，因此模拟谷氨酰胺水解期间形成的γ-谷氨酰硫酯中间体。谷氨酰胺类似物的固定通过几种主要的结构变化激活酶：1）环的闭合以屏蔽谷氨酰胺酶位点，伴随着显著的结构域铰链，2）参与谷氨酰胺水解的催化残基的活化，即Cys-1和Asn-98的α-氨基，其被定位以形成氧阴离子空穴，和3）打开氨通道的Trp-74吲哚基团的75度旋转。
Glucosamine-6P synthase catalyzes the synthesis of glucosamine-6P from fructose-6P and glutamine and uses a channel to transfer ammonia from its glutaminase to its synthase active site. X-ray structures of glucosamine-6P synthase have been determined at 2.05 angstrom resolution in the presence of fructose-6P and at 2.35 angstrom resolution in the presence of fructose-6P and 6-diazo-5-oxo-L-norleucine, a glutamine affinity analog that covalently modifies the N-terminal catalytic cysteine, therefore mimicking the gamma-glutamylthioester intermediate formed during hydrolysis of glutamine. The fixation of the glutamine analog activates the enzyme through several major structural changes: 1) the closure of a loop to shield the glutaminase site accompanied by significant domain hinging, 2) the activation of catalytic residues involved in glutamine hydrolysis, i.e. the alpha-amino group of Cys-1 and Asn-98 that is positioned to form the oxyanion hole, and 3) a 75 degrees rotation of the Trp-74 indole group that opens the ammonia channel.