Torres-Larios Alfredo, Sankaranarayanan Rajan, Rees Bernard, Dock-Bregeon Anne Catherine, Moras Dino
Laboratoire de Biologie et Génomique Structurales, IGBMC, 1 rue Laurent Fries, BP 10142, 67400 Illkirch Cedex, France.
J Mol Biol. 2003 Aug 1;331(1):201-11. doi: 10.1016/s0022-2836(03)00719-8.
The crystal structures of threonyl-tRNA synthetase (ThrRS) from Staphylococcus aureus, with ATP and an analogue of threonyl adenylate, are described. Together with the previously determined structures of Escherichia coli ThrRS with different substrates, they allow a comprehensive analysis of the effect of binding of all the substrates: threonine, ATP and tRNA. The tRNA, by inserting its acceptor arm between the N-terminal domain and the catalytic domain, causes a large rotation of the former. Within the catalytic domain, four regions surrounding the active site display significant conformational changes upon binding of the different substrates. The binding of threonine induces the movement of as much as 50 consecutive amino acid residues. The binding of ATP triggers a displacement, as large as 8A at some C(alpha) positions, of a strand-loop-strand region of the core beta-sheet. Two other regions move in a cooperative way upon binding of threonine or ATP: the motif 2 loop, which plays an essential role in the first step of the aminoacylation reaction, and the ordering loop, which closes on the active site cavity when the substrates are in place. The tRNA interacts with all four mobile regions, several residues initially bound to threonine or ATP switching to a position in which they can contact the tRNA. Three such conformational switches could be identified, each of them in a different mobile region. The structural analysis suggests that, while the small substrates can bind in any order, they must be in place before productive tRNA binding can occur.
本文描述了来自金黄色葡萄球菌的苏氨酰 - tRNA合成酶（ThrRS）与ATP及苏氨酰腺苷酸类似物的晶体结构。结合先前测定的大肠杆菌ThrRS与不同底物的结构，这些结构使得我们能够全面分析所有底物（苏氨酸、ATP和tRNA）结合的影响。tRNA通过将其受体臂插入N端结构域和催化结构域之间，导致前者发生大幅旋转。在催化结构域内，活性位点周围的四个区域在结合不同底物时显示出显著的构象变化。苏氨酸的结合诱导多达50个连续氨基酸残基的移动。ATP的结合引发核心β折叠的一个链 - 环 - 链区域在某些Cα位置发生高达8埃的位移。另外两个区域在结合苏氨酸或ATP时协同移动：在氨酰化反应第一步中起关键作用的模体2环，以及当底物就位时封闭活性位点腔的有序环。tRNA与所有四个可移动区域相互作用，几个最初与苏氨酸或ATP结合的残基切换到能够与tRNA接触的位置。可以识别出三个这样的构象转换，每个转换发生在不同的可移动区域。结构分析表明，虽然小底物可以以任何顺序结合，但它们必须在tRNA有效结合发生之前就位。
