This family includes animal transglutaminases and other bacterial proteins of unknown function. 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' [1]. On the basis of the experimentally demonstrated activity of the Methanobacterium phage pseudomurein endoisopeptidase [2], 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. [3]

1: Three-dimensional structure of a transglutaminase: human blood coagulation factor XIII. Yee VC, Pedersen LC, Le Trong I, Bishop PD, Stenkamp RE, Teller DC; Proc Natl Acad Sci USA 1994;91:7296-7300. PMID:7913750

2: Molecular analysis of Methanobacterium phage psiM2. Pfister P, Wasserfallen A, Stettler R, Leisinger T; Mol Microbiol 1998;30:233-244. PMID:9791169

3: A superfamily of archaeal, bacterial, and eukaryotic proteins homologous to animal transglutaminases [In Process Citation] Makarova KS, Aravind L, Koonin EV; Protein Sci 1999;8:1714-1719. PMID:10452618