Serre L, Verdon G, Choinowski T, Hervouet N, Risler J L, Zelwer C
Centre de Biophysique Moléculaire, Centre National de la Recherche Scientifique, rue Charles Sadron, Orléans Cedex 2, 45071, France.
J Mol Biol. 2001 Mar 2;306(4):863-76. doi: 10.1006/jmbi.2001.4408.
Amino acid selection by aminoacyl-tRNA synthetases requires efficient mechanisms to avoid incorrect charging of the cognate tRNAs. A proofreading mechanism prevents Escherichia coli methionyl-tRNA synthetase (EcMet-RS) from activating in vivo L-homocysteine, a natural competitor of L-methionine recognised by the enzyme. The crystal structure of the complex between EcMet-RS and L-methionine solved at 1.8 A resolution exhibits some conspicuous differences with the recently published free enzyme structure. Thus, the methionine delta-sulphur atom replaces a water molecule H-bonded to Leu13N and Tyr260O(eta) in the free enzyme. Rearrangements of aromatic residues enable the protein to form a hydrophobic pocket around the ligand side-chain. The subsequent formation of an extended water molecule network contributes to relative displacements, up to 3 A, of several domains of the protein. The structure of this complex supports a plausible mechanism for the selection of L-methionine versus L-homocysteine and suggests the possibility of information transfer between the different functional domains of the enzyme.
氨酰 - tRNA合成酶对氨基酸的选择需要有效的机制来避免同源tRNA的错误氨酰化。一种校对机制可防止大肠杆菌甲硫氨酰 - tRNA合成酶（EcMet - RS）在体内激活L - 高半胱氨酸，L - 高半胱氨酸是该酶识别的L - 甲硫氨酸的天然竞争者。以1.8 Å分辨率解析的EcMet - RS与L - 甲硫氨酸复合物的晶体结构与最近发表的游离酶结构存在一些显著差异。因此，甲硫氨酸的δ - 硫原子取代了游离酶中与Leu13N和Tyr260O(η)形成氢键的水分子。芳香族残基的重排使蛋白质能够在配体侧链周围形成一个疏水口袋。随后形成的扩展水分子网络导致蛋白质几个结构域发生高达3 Å的相对位移。该复合物的结构支持了一种合理的L - 甲硫氨酸与L - 高半胱氨酸选择机制，并暗示了酶的不同功能结构域之间信息传递的可能性。
