transamidase

Transamidases are enzymes that catalyze the transfer of an amide group from one molecule to another, forming new amide bonds in the process. In the classic transglutaminase reaction, the amide donor is a glutamine residue within a substrate protein, and the acceptor is an amine such as a lysine side chain or a small amine donor. The process often results in covalent cross-links between proteins and can also attach amines to proteins, altering their function, localization, or stability. Many transamidases require calcium ions for activity and proceed via an acyl-enzyme intermediate at the glutamine side chain.

Prominent examples include the tissue transglutaminase (TG2) and plasma factor XIIIa, a Ca2+-dependent transglutaminase that cross-links fibrin during blood coagulation. A microbial transglutaminase from Streptomyces mobaraensis is widely used commercially to improve the texture and functional properties of protein-containing foods by cross-linking substrate proteins.

Biological roles attributed to transamidases include extracellular matrix stabilization, cell-matrix interactions, wound healing, and protein maturation. In pathology, TG2 has been implicated as an autoantigen in celiac disease and aberrant transamidation activity has been linked to fibrosis and other disorders. The activity of transamidases is a target of research for therapeutics and for biotechnological protein modification.

Detection and measurement typically use amine substrates that become covalently incorporated into proteins; research uses labeled amines to quantify activity and substrate specificity. Transamidases are distinct from amidases and other transferases by their specific amide-transfer chemistry, and they represent a diverse and widely distributed enzyme family across organisms.