InterPro domain: IPR016061

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 [ 1 , 2 ]. These proteins differ widely in size and oligomeric state, and have limited sequence homology [ 3 ]. 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 [ 4 ]. Class II aminoacyl-tRNA synthetases share an anti-parallel beta-sheet fold flanked by alpha-helices [ 5 ], and are mostly dimeric or multimeric, containing at least three conserved regions [ 6 , 7 , 8 ]. However, tRNA binding involves an alpha-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 [ 9 ].

Proline tRNA ligase (also known as Prolyl tRNA synthetase) ( 6.1.1.15 ) exists in two forms, which are loosely related. The first form is present in the majority of eubacteria species. The second one, present in some eubacteria, is essentially present in archaea and eukaryota. Proline-tRNA ligase belongs to class IIa.

This domain is found at the C-terminal in archaeal and eukaryotic enzymes, as well as in certain bacterial ones.

1. Aminoacyl-tRNA synthetases, the genetic code, and the evolutionary process. Microbiol. Mol. Biol. Rev. 64, 202-36
2. Aminoacyl-tRNA synthetases: versatile players in the changing theater of translation. RNA 8, 1363-72
3. Partition of tRNA synthetases into two classes based on mutually exclusive sets of sequence motifs. Nature 347, 203-6
4. The 2.0 A crystal structure of Thermus thermophilus methionyl-tRNA synthetase reveals two RNA-binding modules. Structure 8, 197-208
5. Structural basis for transfer RNA aminoacylation by Escherichia coli glutaminyl-tRNA synthetase. Biochemistry 32, 8758-71
6. The aminoacyl-tRNA synthetase family: modules at work. Bioessays 15, 675-87
7. Classes of aminoacyl-tRNA synthetases and the establishment of the genetic code. Trends Biochem. Sci. 16, 1-3
8. Sequence, structural and evolutionary relationships between class 2 aminoacyl-tRNA synthetases. Nucleic Acids Res. 19, 3489-98
9. Evolution of aminoacyl-tRNA synthetases--analysis of unique domain architectures and phylogenetic trees reveals a complex history of horizontal gene transfer events. Genome Res. 9, 689-710