Peisach D, Chipman D M, Van Ophem P W, Manning J M, Ringe D
Program in Bioorganic Chemistry, Brandeis University, 415 South Street, Waltham, Massachusetts 02254-9110, USA.
Biochemistry. 1998 Apr 7;37(14):4958-67. doi: 10.1021/bi972884d.
The three-dimensional structures of two forms of the D-amino acid aminotransferase (D-aAT) from Bacillus sp. YM-1 have been determined crystallographically: the pyridoxal phosphate (PLP) form and a complex with the reduced analogue of the external aldimine, N-(5'-phosphopyridoxyl)-d-alanine (PPDA). Together with the previously reported pyridoxamine phosphate form of the enzyme [Sugio et al. (1995) Biochemistry 34, 9661], these structures allow us to describe the pathway of the enzymatic reaction in structural terms. A major determinant of the enzyme's stereospecificity for D-amino acids is a group of three residues (Tyr30, Arg98, and His100, with the latter two contributed by the neighboring subunit) forming four hydrogen bonds to the substrate alpha-carboxyl group. The replacement by hydrophobic groups of the homologous residues of the branched chain L-amino acid aminotransferase (which has a similar fold) could explain its opposite stereospecificity. As in L-aspartate aminotransferase (L-AspAT), the cofactor in D-aAT tilts (around its phosphate group and N1 as pivots) away from the catalytic lysine 145 and the protein face in the course of the reaction. Unlike L-AspAT, D-aAT shows no other significant conformational changes during the reaction.
已通过晶体学方法确定了来自芽孢杆菌属YM-1的两种形式的D-氨基酸转氨酶（D-aAT）的三维结构：磷酸吡哆醛（PLP）形式以及与外部醛亚胺的还原类似物N-(5'-磷酸吡哆基)-D-丙氨酸（PPDA）的复合物。连同先前报道的该酶的磷酸吡哆胺形式[杉尾等人（1995年），《生物化学》34卷，9661页]，这些结构使我们能够从结构角度描述酶促反应的途径。该酶对D-氨基酸的立体特异性的一个主要决定因素是由三个残基（Tyr30、Arg98和His100，后两个残基由相邻亚基提供）组成的基团，该基团与底物α-羧基形成四个氢键。支链L-氨基酸转氨酶（具有相似的折叠结构）的同源残基被疏水基团取代，可以解释其相反的立体特异性。与L-天冬氨酸转氨酶（L-AspAT）一样，D-aAT中的辅因子在反应过程中（围绕其磷酸基团和N1作为枢轴）从催化赖氨酸145和蛋白质表面倾斜离开。与L-AspAT不同，D-aAT在反应过程中没有其他明显的构象变化。
