Dock-Bregeon Anne-Catherine, Rees Bernard, Torres-Larios Alfredo, Bey Gilbert, Caillet Joel, Moras Dino
IGBMC (CNRS/INSERM/Université Louis Pasteur), Laboratoire de Biologie et Génomique Structurales, 1, rue Laurent Fries, BP 10142, 67400 Illkirch, France.
Mol Cell. 2004 Nov 5;16(3):375-86. doi: 10.1016/j.molcel.2004.10.002.
The fidelity of aminoacylation of tRNA(Thr) by the threonyl-tRNA synthetase (ThrRS) requires the discrimination of the cognate substrate threonine from the noncognate serine. Misacylation by serine is corrected in a proofreading or editing step. An editing site has been located 39 A away from the aminoacylation site. We report the crystal structures of this editing domain in its apo form and in complex with the serine product, and with two nonhydrolyzable analogs of potential substrates: the terminal tRNA adenosine charged with serine, and seryl adenylate. The structures show how serine is recognized, and threonine rejected, and provide the structural basis for the editing mechanism, a water-mediated hydrolysis of the mischarged tRNA. When the adenylate analog binds in the editing site, a phosphate oxygen takes the place of one of the catalytic water molecules, thereby blocking the reaction. This rules out a correction mechanism that would occur before the binding of the amino acid on the tRNA.
苏氨酰 - tRNA合成酶（ThrRS）对tRNA(Thr)进行氨酰化的保真度要求能够区分同源底物苏氨酸和非同源丝氨酸。丝氨酸造成的错误氨酰化会在校读或编辑步骤中得到纠正。一个编辑位点位于距氨酰化位点39埃处。我们报道了该编辑结构域的无配体形式以及与丝氨酸产物、两种潜在底物的非水解类似物（即丝氨酸化的tRNA末端腺苷和丝氨酰腺苷酸）形成复合物时的晶体结构。这些结构展示了丝氨酸是如何被识别而苏氨酸被排斥的，并为编辑机制（即对错误氨酰化的tRNA进行水介导的水解）提供了结构基础。当腺苷酸类似物结合在编辑位点时，一个磷酸氧取代了其中一个催化水分子，从而阻断了反应。这排除了在氨基酸结合到tRNA之前发生校正机制的可能性。
