Structural basis for the catalysis and substrate specificity of homoserine kinase
Structural basis for the catalysis and substrate specificity of homoserine kinase
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DOI：
10.1021/bi010851z
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发表时间：
2001-09-11
期刊：
影响因子：
2.9
通讯作者：
Zhang, H
中科院分区：
文献类型：
--
作者：
Krishna, SS;Zhou, T;Zhang, H
高丝氨酸激酶 (HSK) 是氨基酸生物合成天冬氨酸途径中的第四种酶，催化 L-高丝氨酸 (Hse) 磷酸化为 L-高丝氨酸磷酸盐，L-高丝氨酸磷酸盐是 L-苏氨酸、L-异亮氨酸和高等植物中 L-蛋氨酸生产的中间体。詹氏甲烷球菌 HSK 三元复合物及其氨基酸底物和 ATP 类似物的高分辨率结构已通过 X 射线晶体学测定。这些结构揭示了 Hse 紧密且高度特异性结合的结构决定因素，其与局部构象相结合。强制隔离底物的变化。结合的 Hse 的 δ-羟基距离结合的核苷酸的 γ-磷酸仅 3.4 A，准备好对 γ-磷进行串联攻击。结合的核苷酸在三磷酸尾部是柔性的。然而，Mg2+ 位于具有良好配体几何形状的核苷酸的β-和γ-磷酸盐之间结合的复合物之一中，并由Glu130 的侧链协调。磷酰基受体羟基附近不能有强亲核试剂（碱基）。因此，我们提出HSK的催化机制不涉及激活磷酰基受体羟基的催化碱，而是通过过渡态稳定机制介导。
Homoserine kinase (HSK), the fourth enzyme in the aspartate pathway of amino acid biosynthesis, catalyzes the phosphorylation Of L-homoserine (Hse) to L-homoserine phosphate, an intermediate in the production Of L-threonine, L-isoleucine, and in higher plants, L-Methionine. The high-resolution structures of Methanococcus jannaschii HSK ternary complexes with its amino acid substrate and ATP analogues have been determined by X-ray crystallography. These structures reveal the structural determinants of the tight and highly specific binding of Hse, which is coupled with local conformational. changes that enforce the sequestration of the substrate. The delta -hydroxyl group of bound Hse is only 3.4 A away from the gamma -phosphate of the bound nucleotide, poised for the in-line attack at the gamma -phosphorus. The bound nucleotides are flexible at the triphosphate tail. Nevertheless, a Mg2+ was located in one of the complexes that binds between the beta- and gamma -phosphates of the nucleotide with good ligand geometry and is coordinated by the side chain of Glu130. No strong nucleophile (base) can be located near the phosphoryl acceptor hydroxyl group. Therefore, we propose that the catalytic mechanism of HSK does not involve a catalytic base for activating the phosphoryl acceptor hydroxyl but instead is mediated via a transition state stabilization mechanism.