ABSTRACT
The gene encoding melamine deaminase (TriA) from
Pseudomonas
sp. strain NRRL B-12227 was identified, cloned into
Escherichia coli
, sequenced, and expressed for in vitro study of enzyme activity. Melamine deaminase displaced two of the three amino groups from melamine, producing ammeline and ammelide as sequential products. The first deamination reaction occurred more than 10 times faster than the second. Ammelide did not inhibit the first or second deamination reaction, suggesting that the lower rate of ammeline hydrolysis was due to differential substrate turnover rather than product inhibition. Remarkably, melamine deaminase is 98% identical to the enzyme atrazine chlorohydrolase (AtzA) from
Pseudomonas
sp. strain ADP. Each enzyme consists of 475 amino acids and differs by only 9 amino acids. AtzA was shown to exclusively catalyze dehalogenation of halo-substituted triazine ring compounds and had no activity with melamine and ammeline. Similarly, melamine deaminase had no detectable activity with the halo-triazine substrates. Melamine deaminase was active in deamination of a substrate that was structurally identical to atrazine, except for the substitution of an amino group for the chlorine atom. Moreover, melamine deaminase and AtzA are found in bacteria that grow on melamine and atrazine compounds, respectively. These data strongly suggest that the 9 amino acid differences between melamine deaminase and AtzA represent a short evolutionary pathway connecting enzymes catalyzing physiologically relevant deamination and dehalogenation reactions, respectively.
摘要
编码三聚氰胺脱氨酶(TriA)基因的
假单胞菌
菌株 NRRL B-12227 中三聚氰胺脱氨酶(TriA)的编码基因被鉴定并克隆到
大肠杆菌
测序,并表达用于体外酶活性研究。三聚氰胺脱氨酶从三聚氰胺中移除三个氨基中的两个,依次生成氨线和酰胺。第一次脱氨基反应的速度比第二次快 10 倍以上。酰胺内酯对第一个或第二个脱氨基反应没有抑制作用,这表明较低的酰胺水解速率是由于底物周转率不同而不是产物抑制所致。值得注意的是,三聚氰胺脱氨酶与来自假单胞菌的阿特拉津氯水解酶(AtzA)有 98% 的相同之处。
假单胞菌
菌株 ADP 的阿特拉津氯水解酶(AtzA)有 98% 的相同之处。每种酶由 475 个氨基酸组成,只有 9 个氨基酸不同。研究表明,AtzA 只催化卤代三嗪环化合物的脱卤作用,对三聚氰胺和二甲氨基酚没有活性。同样,三聚氰胺脱氨酶对卤代三嗪底物也没有可检测到的活性。三聚氰胺脱氨酶对结构上与阿特拉津相同的底物具有脱氨活性,只是用一个氨基取代了氯原子。此外,三聚氰胺脱氨酶和 AtzA 分别存在于在三聚氰胺和阿特拉津化合物上生长的细菌中。这些数据有力地表明,三聚氰胺脱氨酶和 AtzA 之间的 9 个氨基酸差异代表了连接分别催化生理相关脱氨和脱卤反应的酶的一条短进化途径。