Protein Domain : Lysine-tRNA ligase IPR002904

Type	Family
Description	Lysine-tRNA ligase (also known as Lysyl-tRNA synthetase) ( ) is an alpha 2 homodimer that belong to both class I and class II. In eubacteria and eukaryota lysine-tRNA ligases belong to class II in the same family as aspartyl tRNA ligase. The class Ic lysine-tRNA ligase family is present in archaea and in a number of bacterial groups that include the alphaproteobacteria and spirochaetes[ ]. A refined crystal structures shows that the active site of LysU is shaped to position the substrates for the nucleophilic attack of the lysine carboxylate on the ATP alpha-phosphate. No residues are directly involved in catalysis, but a number of highly conserved amino acids and three metal ions coordinate the substrates and stabilise the pentavalent transition state. A loop close to the catalytic pocket, disordered in the lysine-bound structure, becomes ordered upon adenine binding [].The aminoacyl-tRNA synthetases (also known as aminoacyl-tRNA ligases) catalyse the attachment of an amino acid to its cognate transfer RNA molecule in a highly specific two-step reaction [ , ]. These proteins differ widely in size and oligomeric state, and have limited sequence homology []. The 20 aminoacyl-tRNA synthetases are divided into two classes, I and II. Class I aminoacyl-tRNA synthetases contain a characteristic Rossman fold catalytic domain and are mostly monomeric []. Class II aminoacyl-tRNA synthetases share an anti-parallel β-sheet fold flanked by α-helices [], and are mostly dimeric or multimeric, containing at least three conserved regions [, , ]. However, tRNA binding involves an α-helical structure that is conserved between class I and class II synthetases. In reactions catalysed by the class I aminoacyl-tRNA synthetases, the aminoacyl group is coupled to the 2'-hydroxyl of the tRNA, while, in class II reactions, the 3'-hydroxyl site is preferred. The synthetases specific for arginine, cysteine, glutamic acid, glutamine, isoleucine, leucine, methionine, tyrosine, tryptophan, valine, and some lysine synthetases (non-eukaryotic group) belong to class I synthetases. The synthetases specific for alanine, asparagine, aspartic acid, glycine, histidine, phenylalanine, proline, serine, threonine, and some lysine synthetases (non-archaeal group), belong to class-II synthetases. Based on their mode of binding to the tRNA acceptor stem, both classes of tRNA synthetases have been subdivided into three subclasses, designated 1a, 1b, 1c and 2a, 2b, 2c [].
Short Name	Lys-tRNA-ligase