Okamoto A, Higuchi T, Hirotsu K, Kuramitsu S, Kagamiyama H
Department of Chemistry, Faculty of Science, Osaka City University.
J Biochem. 1994 Jul;116(1):95-107. doi: 10.1093/oxfordjournals.jbchem.a124509.
We determined the three-dimensional structures of aspartate aminotransferase (AspAT) from Escherichia coli and its complex with inhibitor (2-methyl-L-aspartate) at 1.8A resolution. This enzyme reversibly catalyzes the transamination reaction and is a dimer of two identical subunits. Each subunit has 396 amino acid residues and one pyridoxal 5'-phosphate as a cofactor, and is divided into two domains, one large and the other small. Upon binding of the inhibitor, the small domain rotates by 5 degrees toward the large domain to close the active site. This domain movement is caused mainly by small but important main-chain conformational changes in the residues located over the domain interface of the small domain. In chicken mitochondrial AspAT, the domain movement was larger, with a rotational angle of 13 degrees. By comparison of these two structures, the difference in the rotational angles was found to be caused by the larger opening of the domain in the open form of chicken mitochondrial AspAT. Although the overall structures of these two enzymes were almost identical, the surface area of the domain interface in the E. coli enzyme was larger than that in mitochondrial AspAT, suggesting that the structure of the domain interface is responsible for the degree of movement of the small domain.
我们测定了来自大肠杆菌的天冬氨酸转氨酶（AspAT）及其与抑制剂（2-甲基-L-天冬氨酸）复合物的三维结构，分辨率为1.8埃。该酶可逆地催化转氨基反应，是由两个相同亚基组成的二聚体。每个亚基有396个氨基酸残基和一个磷酸吡哆醛作为辅因子，分为两个结构域，一个大结构域和一个小结构域。抑制剂结合后，小结构域向大结构域旋转5度以关闭活性位点。这种结构域运动主要是由小结构域结构域界面上方残基中微小但重要的主链构象变化引起的。在鸡线粒体AspAT中，结构域运动更大，旋转角度为13度。通过比较这两种结构，发现旋转角度的差异是由鸡线粒体AspAT开放形式中结构域更大的开口引起的。尽管这两种酶的整体结构几乎相同，但大肠杆菌酶中结构域界面的表面积大于线粒体AspAT中的表面积，这表明结构域界面的结构决定了小结构域的运动程度。
