Aminoacyl tRNA synthetases, class II

{{Short description|Protein family}}

{{Infobox protein family

|Symbol = Aa-tRNA-synt_II

|Name = Aminoacyl-tRNA synthetase, class II

|Pfam = PF00152

|InterPro = IPR006195

|PROSITE =

|CDD = cd00768

|PDB = {{PDB|1asy}} {{PDB|1asz}} {{PDB|1b8a}} {{PDB|1bbu}} {{PDB|1bbw}} {{PDB|1c0a}} {{PDB|1e1o}} {{PDB|1e1t}} {{PDB|1e22}} {{PDB|1e24}}

}}

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.{{cite journal |vauthors=Delarue M, Moras D, Poch O, Eriani G, Gangloff J |title=Partition of tRNA synthetases into two classes based on mutually exclusive sets of sequence motifs |journal=Nature |volume=347 |issue=6289 |pages=203–206 |year=1990 |pmid=2203971 |doi=10.1038/347203a0|bibcode=1990Natur.347..203E |s2cid=4324290 }}

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.{{cite journal |vauthors=Moras D, Konno M, Shimada A, Nureki O, Tateno M, Yokoyama S, Sugiura I, Ugaji-Yoshikawa Y, Kuwabara S, Lorber B, Giege R |title=The 2.0 A crystal structure of Thermus thermophilus methionyl-tRNA synthetase reveals two RNA-binding modules |journal=Structure |volume=8 |issue=2 |pages=197–208 |year=2000 |pmid=10673435 |doi=10.1016/S0969-2126(00)00095-2|doi-access=free }} Class II aminoacyl-tRNA synthetases share an anti-parallel beta-sheet fold flanked by alpha-helices,{{cite journal |vauthors=Perona JJ, Steitz TA, Rould MA |title=Structural basis for transfer RNA aminoacylation by Escherichia coli glutaminyl-tRNA synthetase |journal=Biochemistry |volume=32 |issue=34 |pages=8758–8771 |year=1993 |pmid=8364025 |doi=10.1021/bi00085a006}} and are mostly dimeric or multimeric, containing at least three conserved regions.{{cite journal |vauthors=Delarue M, Moras D |title=The aminoacyl-tRNA synthetase family: modules at work |journal=BioEssays |volume=15 |issue=10 |pages=675–687 |year=1993 |pmid=8274143 |doi=10.1002/bies.950151007|s2cid=35612984 }}{{cite journal |author =Schimmel P |title=Classes of aminoacyl-tRNA synthetases and the establishment of the genetic code |journal=Trends Biochem. Sci. |volume=16 |issue=1 |pages=1–3 |year=1991 |pmid=2053131 |doi=10.1016/0968-0004(91)90002-D}}{{cite journal |vauthors=Cusack S, Leberman R, Hartlein M |title=Sequence, structural and evolutionary relationships between class 2 aminoacyl-tRNA synthetases |journal=Nucleic Acids Res. |volume=19 |issue=13 |pages=3489–3498 |year=1991 |pmid=1852601 |doi=10.1093/nar/19.13.3489 |pmc=328370}} 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.{{cite journal |author =Bairoch A |title=List of aminoacyl-tRNA synthetases |year=2004}}