TGc

Transglutaminase/protease-like homologues
TGc
SMART accession number:SM00460
Description: Transglutaminases are enzymes that establish covalent links between proteins. A subset of transglutaminase homologues appear to catalyse the reverse reaction, the hydrolysis of peptide bonds. Proteins with this domain are both extracellular and intracellular, and it is likely that the eukaryotic intracellular proteins are involved in signalling events.
Interpro abstract (IPR002931):

This domain is found in many proteins known to have transglutaminase activity, i.e. which cross-link proteins through an acyl-transfer reaction between the gamma-carboxamide group of peptide-bound glutamine and the epsilon-amino group of peptide-bound lysine, resulting in a epsilon-(gamma-glutamyl)lysine isopeptide bond. Tranglutaminases have been found in a diverse range of species, from bacteria through to mammals. The enzymes require calcium binding and their activity leads to post-translational modification of proteins through acyl-transfer reactions, involving peptidyl glutamine residues as acyl donors and a variety of primary amines as acyl acceptors, with the generation of proteinase resistant isopeptide bonds [(PUBMED:12366374)].

Sequence conservation in this superfamily primarily involves three motifs that centre around conserved cysteine, histidine, and aspartate residues that form the catalytic triad in the structurally characterised transglutaminase, the human blood clotting factor XIIIa' [(PUBMED:7913750)]. On the basis of the experimentally demonstrated activity of the Methanobacterium phage psiM2 pseudomurein endoisopeptidase [(PUBMED:9791169)], it is proposed that many, if not all, microbial homologues of the transglutaminases are proteases and that the eukaryotic transglutaminases have evolved from an ancestral protease [(PUBMED:10452618)].

A subunit of plasma Factor XIII revealed that each Factor XIIIA subunit is composed of four domains (termed N-terminal beta-sandwich, core domain (containing the catalytic and the regulatory sites), and C-terminal beta-barrels 1 and 2) and that two monomers assemble into the native dimer through the surfaces in domains 1 and 2, in opposite orientation. This organisation in four domains is highly conserved during evolution among transglutaminase isoforms [(PUBMED:12366374)].

Family alignment:
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There are 8134 TGc domains in 8115 proteins in SMART's nrdb database.

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