Phenylalanine-tRNA ligase, class IIc, beta subunit (IPR004532)

Short name: Phe-tRNA-ligase_IIc_bsu

Overlapping homologous superfamilies


Family relationships



Phenylalanine-tRNA ligase (EC: is an alpha2/beta2 tetramer composed of 2 subunits that belongs to class IIc. In eubacteria, a small subunit (pheS gene) can be designated as beta (E. coli) or alpha subunit (see IPR002319). Reciprocally the large subunit (pheT gene) can be designated as alpha (E. coli) or beta. In all other kingdoms the two subunits have equivalent length in eukaryota, and can be identified by specific signatures. The enzyme from Thermus thermophilus has an alpha 2 beta 2 type quaternary structure and is one of the most complicated members of the synthetase family. Identification of phenylalanine-tRNA ligase as a member of class II aaRSs was based only on sequence alignment of the small alpha-subunit with other ligases [PMID: 8199244].

This family describes the beta subunit. The beta subunits break into two subfamilies that are considerably different in sequence, length, and pattern of gaps (see also IPR004531). This family represents the subfamily that includes the beta subunit from bacteria other than spirochetes, as well as a chloroplast-encoded form from Porphyra purpurea. The chloroplast-derived sequence is considerably shorter at the N-terminal.

The aminoacyl-tRNA synthetase (also known as aminoacyl-tRNA ligase) catalyse the attachment of an amino acid to its cognate transfer RNA molecule in a highly specific two-step reaction [PMID: 10704480,PMID: 12458790]. These proteins differ widely in size and oligomeric state, and have limited sequence homology [PMID: 2203971]. 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 [PMID: 10673435]. Class II aminoacyl-tRNA synthetases share an anti-parallel beta-sheet fold flanked by alpha-helices [PMID: 8364025], and are mostly dimeric or multimeric, containing at least three conserved regions [PMID: 8274143, PMID: 2053131, PMID: 1852601]. 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 [PMID: 10447505].

GO terms

Biological Process

GO:0006432 phenylalanyl-tRNA aminoacylation

Molecular Function

GO:0005524 ATP binding
GO:0000287 magnesium ion binding
GO:0004826 phenylalanine-tRNA ligase activity

Cellular Component

GO:0005737 cytoplasm

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.