Arnez J G, Sankaranarayanan R, Dock-Bregeon A C, Francklyn C S, Moras D
a Laboratoire de Biologie Structurale , Institut de Génétique et de Biologie Moléculaire et Cellulaire , CNRS/INSERM/ULP, BP 163 , 67404 , Illkirch Cedex , France.
J Biomol Struct Dyn. 2000;17 Suppl 1:23-7. doi: 10.1080/07391102.2000.10506600.
Abstract The crystal structures of histidyl- (HisRS) and threonyl-tRNA synthetase (ThrRS) from E. coli and glycyl-tRNA synthetase (GlyRS) from T. thermophilus, all homodimeric class IIa enzymes, were determined in enzyme-substrate and enzyme-product states corresponding to the two steps of aminoacylation. HisRS was complexed with the histidine analog histidinol plus ATP and with histidyl-adenylate, while GlyRS was complexed with ATP and with glycyl-adenylate; these complexes represent the enzyme-substrate and enzyme-product states of the first step of aminoacylation, i.e. the amino acid activation. In both enzymes the ligands occupy the substrate-binding pocket of the N-terminal active site domain, which contains the classical class II aminoacyl-tRNA synthetase fold. HisRS interacts in the same fashion with the histidine, adenosine and α-phosphate moieties of the substrates and intermediate, and GlyRS interacts in the same way with the adenosine and α-phosphate moieties in both states. In addition to the amino acid recognition, there is one key mechanistic difference between the two enzymes: HisRS uses an arginine whereas GlyRS employs a magnesium ion to catalyze the activation of the amino acid. ThrRS was complexed with its cognate tRNA and ATP, which represents the enzyme-substrate state of the second step of aminoacylation, i.e. the transfer of the amino acid to the 3'-terminal ribose of the tRNA. All three enzymes utilize class II conserved residues to interact with the adenosine-phosphate. ThrRS binds tRNA(Thr) so that the acceptor stem enters the active site pocket above the adenylate, with the 3'-terminal OH positioned to pick up the amino acid, and the anticodon loop interacts with the C-terminal domain whose fold is shared by all three enzymes. We can thus extend the principles of tRNA binding to the other two enzymes.
摘要 测定了来自大肠杆菌的组氨酰 - tRNA合成酶（HisRS）和苏氨酰 - tRNA合成酶（ThrRS）以及嗜热栖热菌的甘氨酰 - tRNA合成酶（GlyRS）的晶体结构，这三种酶均为同二聚体IIa类酶，其晶体结构是在与氨酰化两步反应相对应的酶 - 底物和酶 - 产物状态下测定的。HisRS与组氨酸类似物组氨醇加ATP以及组氨酰 - 腺苷酸形成复合物，而GlyRS与ATP以及甘氨酰 - 腺苷酸形成复合物；这些复合物代表氨酰化第一步即氨基酸活化的酶 - 底物和酶 - 产物状态。在这两种酶中，配体占据N端活性位点结构域的底物结合口袋，该结构域包含经典的II类氨酰 - tRNA合成酶折叠。HisRS以相同方式与底物和中间体的组氨酸、腺苷和α - 磷酸部分相互作用，并且GlyRS在两种状态下均以相同方式与腺苷和α - 磷酸部分相互作用。除了氨基酸识别外，这两种酶之间存在一个关键的机制差异：HisRS使用精氨酸而GlyRS利用镁离子催化氨基酸的活化。ThrRS与其同源tRNA和ATP形成复合物，这代表氨酰化第二步即氨基酸转移到tRNA的3' - 末端核糖上的酶 - 底物状态。所有这三种酶都利用II类保守残基与腺苷 - 磷酸相互作用。ThrRS结合tRNA(Thr)，使得受体茎进入腺苷酸上方的活性位点口袋，3' - 末端OH定位以接受氨基酸，并且反密码子环与C端结构域相互作用，所有这三种酶都具有该结构域的折叠。因此，我们可以将tRNA结合的原理扩展到其他两种酶。
