Microbial transglutaminase (MTG) catalyses an acyl transfer reaction by means of a Cys-Asp diad mechanism, in which the gamma-carboxyamide groups of peptide-bound glutamine residues act as the acyl donors. The MTG molecule forms a single, compact domain belonging to the alpha+beta folding class, containing 11 alpha-helices and 8 beta-strands. The alpha-helices and the beta-strands are concentrated mainly at the amino and carboxyl ends of the polypeptide, respectively. These secondary structures are arranged so that a beta-sheet is surrounded by alpha-helices, which are clustered into three regions [1].

1: Crystal structure of microbial transglutaminase from Streptoverticillium mobaraense. Kashiwagi T, Yokoyama K, Ishikawa K, Ono K, Ejima D, Matsui H, Suzuki E; J Biol Chem. 2002;277:44252-44260. PMID:12221081