Schwede T F, Rétey J, Schulz G E
Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität, Freiburg im Breisgau, Germany.
Biochemistry. 1999 Apr 27;38(17):5355-61. doi: 10.1021/bi982929q.
Histidine ammonia-lyase (EC 4.3.1.3) catalyzes the nonoxidative elimination of the alpha-amino group of histidine and is closely related to the important plant enzyme phenylalanine ammonia-lyase. The crystal structure of histidase from Pseudomonas putida was determined at 2.1 A resolution revealing a homotetramer with D2 symmetry, the molecular center of which is formed by 20 nearly parallel alpha-helices. The chain fold, but not the sequence, resembles those of fumarase C and related proteins. The structure shows that the reactive electrophile is a 4-methylidene-imidazole-5-one, which is formed autocatalytically by cyclization and dehydration of residues 142-144 with the sequence Ala-Ser-Gly. With respect to the first dehydration step, this modification resembles the chromophore of the green fluorescent protein. The active center is clearly established by the modification and by mutations. The observed geometry allowed us to model the bound substrate at a high confidence level. A reaction mechanism is proposed.
组氨酸解氨酶（EC 4.3.1.3）催化组氨酸α-氨基的非氧化消除反应，并且与重要的植物酶苯丙氨酸解氨酶密切相关。恶臭假单胞菌组氨酸酶的晶体结构在2.1 Å分辨率下得以确定，显示出具有D2对称性的同四聚体，其分子中心由20个近乎平行的α螺旋构成。其链折叠方式与延胡索酸酶C及相关蛋白质相似，但序列不同。该结构表明，反应性亲电试剂是一个4-亚甲基咪唑-5-酮，它由142 - 144位残基（序列为丙氨酸-丝氨酸-甘氨酸）通过环化和脱水自动催化形成。就第一步脱水反应而言，这种修饰类似于绿色荧光蛋白的发色团。通过这种修饰和突变明确建立了活性中心。所观察到的几何结构使我们能够在高置信度水平上对结合底物进行建模。并提出了一种反应机制。
