Omi Rie, Goto Masaru, Miyahara Ikuko, Mizuguchi Hiroyuki, Hayashi Hideyuki, Kagamiyama Hiroyuki, Hirotsu Ken
Department of Chemistry, Graduate School of Science, Osaka City University, Osaka 558-8585, Japan.
J Biol Chem. 2003 Nov 14;278(46):46035-45. doi: 10.1074/jbc.M308065200. Epub 2003 Sep 2.
Threonine synthase, which is a PLP-dependent enzyme, catalyzes the beta,gamma-replacement reaction of l-homoserine phosphate to yield threonine and inorganic phosphate. The three-dimensional structures of the enzyme from Thermus thermophilus HB8 in its unliganded form and complexed with the substrate analogue 2-amino-5-phosphonopentanoic acid have been determined at 2.15 and 2.0 A resolution, respectively. The complexed form, assigned as an enamine, uncovered the interactions of the cofactor-analogue conjugate with the active site residues. The binding of the substrate analogue induces a large conformational change at the domain level. The small domain rotates by about 25 degrees and approaches the large domain to close the active site. The complicated catalytic process of the enzyme has been elucidated based on the complex structure to reveal the stereochemistry of the reaction and to present the released inorganic phosphate as a possible catalyst to carry a proton to the Cgamma atom of the substrate.
苏氨酸合酶是一种依赖于磷酸吡哆醛的酶，催化L-高丝氨酸磷酸的β,γ-取代反应，生成苏氨酸和无机磷酸。嗜热栖热菌HB8来源的该酶在无配体形式以及与底物类似物2-氨基-5-膦酰基戊酸结合的复合物形式下的三维结构，分别在2.15 Å和2.0 Å分辨率下得以确定。复合物形式被认定为烯胺，揭示了辅因子类似物共轭物与活性位点残基之间的相互作用。底物类似物的结合在结构域水平上诱导了较大的构象变化。小结构域旋转约25度并靠近大结构域以封闭活性位点。基于复合物结构阐明了该酶复杂的催化过程，以揭示反应的立体化学，并提出释放的无机磷酸可能作为一种催化剂，将一个质子传递到底物的Cγ原子上。
