Aminoacyl tRNA synthetases, class II explained

Aminoacyl-tRNA synthetases, class II is a family of proteins. These proteins 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 a 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 catalytic domain and are mostly monomeric.^[2] Class II aminoacyl-tRNA synthetases share an anti-parallel beta-sheet fold flanked by alpha-helices,^[3] and are mostly dimeric or multimeric, containing at least three conserved regions.^{[4] [5] [6]} 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 and valine belong to class I synthetases; these synthetases are further divided into three subclasses, a, b and c, according to sequence homology. The synthetases specific for alanine, asparagine, aspartic acid, glycine, histidine, lysine, phenylalanine, proline, serine, and threonine belong to class-II synthetases.^[7]

Human proteins containing this domain

• DARS
• DARS2
• KARS
• NARS
• NARS2

Notes and References

1. Delarue M, Moras D, Poch O, Eriani G, Gangloff J . Partition of tRNA synthetases into two classes based on mutually exclusive sets of sequence motifs . Nature . 347 . 6289 . 203–206 . 1990 . 2203971 . 10.1038/347203a0. 1990Natur.347..203E . 4324290 .
2. Moras D, Konno M, Shimada A, Nureki O, Tateno M, Yokoyama S, Sugiura I, Ugaji-Yoshikawa Y, Kuwabara S, Lorber B, Giege R . The 2.0 A crystal structure of Thermus thermophilus methionyl-tRNA synthetase reveals two RNA-binding modules . Structure . 8 . 2 . 197–208 . 2000 . 10673435 . 10.1016/S0969-2126(00)00095-2. free .
3. Perona JJ, Steitz TA, Rould MA . Structural basis for transfer RNA aminoacylation by Escherichia coli glutaminyl-tRNA synthetase . Biochemistry . 32 . 34 . 8758–8771 . 1993 . 8364025 . 10.1021/bi00085a006.
4. Delarue M, Moras D . The aminoacyl-tRNA synthetase family: modules at work . BioEssays . 15 . 10 . 675–687 . 1993 . 8274143 . 10.1002/bies.950151007. 35612984 .
5. Schimmel P . Classes of aminoacyl-tRNA synthetases and the establishment of the genetic code . Trends Biochem. Sci. . 16 . 1 . 1–3 . 1991 . 2053131 . 10.1016/0968-0004(91)90002-D.
6. Cusack S, Leberman R, Hartlein M . Sequence, structural and evolutionary relationships between class 2 aminoacyl-tRNA synthetases . Nucleic Acids Res. . 19 . 13 . 3489–3498 . 1991 . 1852601 . 10.1093/nar/19.13.3489 . 328370.
7. Bairoch A . List of aminoacyl-tRNA synthetases . 2004.