InterPro domain: IPR015944

The aminoacyl-tRNA synthetases ( 6.1.1 ) 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 [ 1 ]. The 20 aminoacyl-tRNA synthetases are divided into two classes, I and II. Class I aminoacyl-tRNA synthetases contain a characteristic Rossman fold and are mostly monomeric, while class II aminoacyl-tRNA synthetases share an anti-parallel beta-sheet formation, flanked by alpha-helices [ 2 ], and are mostly dimeric or multimeric. 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 aci, glutamine, isoleucine, leucine, methionine, tyrosine, tryptophan and valine belong to class I synthetases. The synthetases specific for alanine, asparagine, aspartic acid, glycine, histidine, lysine, phenylalanine, proline, serine, and threonine belong to class-II synthetases.

The 10 class I synthetases are considered to have in common the catalytic domain structure based on the Rossmann fold, which is totally different from the class II catalytic domain structure. The class I synthetases are further divided into three subclasses, a, b and c, according to sequence homology. No conserved structural features for tRNA recognition by class I synthetases have been established.

This entry represents the beta subunit of glycine-tRNA ligase.

In most eubacteria, glycine-tRNA ligase ( 6.1.1.14 ) is an alpha2/beta2 tetramer composed of 2 different subunits [ 3 , 4 , 5 ] while in archaea, eukaryota and some eubacteria, glycine-tRNA ligase is an alpha2 dimer (see IPR002315 ). This entry represents the beta subunit of the tetrameric enzyme. What is most interestingis the lack of similarity between the two types: divergence at the sequencelevel is so great that it is impossible to infer descent from common genes. The alpha (see IPR002310 ) and beta subunits also lack significant sequence similarity.However, they are translated from a single mRNA [ 6 ], and a single chain glycine-tRNA ligase from Chlamydia trachomatis has been found to have significant similarity with both domains, suggesting divergence from a single polypeptide chain [ 6 ].

1. Partition of tRNA synthetases into two classes based on mutually exclusive sets of sequence motifs. Nature 347, 203-6
2. Structural basis for transfer RNA aminoacylation by Escherichia coli glutaminyl-tRNA synthetase. Biochemistry 32, 8758-71
3. Primary structures of both subunits of Escherichia coli glycyl-tRNA synthetase. J. Biol. Chem. 258, 10637-41
4. Human glycyl-tRNA synthetase. Wide divergence of primary structure from bacterial counterpart and species-specific aminoacylation. J. Biol. Chem. 269, 30049-55
5. The glycyl-tRNA synthetase of Chlamydia trachomatis. J. Bacteriol. 177, 5179-85