Transglutaminase-mediated covalent attachment of polyamines to proteins: mechanisms and potential physiological significance.

Putrescine, spermidine, and spermine can be covalently incorporated as the corresponding peptide-bound gamma-glutamyl-polyamine derivatives into selected glutaminyl residues in proteins and polypeptides that serve as amine acceptor substrates for various calcium-dependent transglutaminases. Once aliphatic diamines or polyamines have been enzymatically incorporated into polypeptides in that fashion, the remaining free primary amino groups can undergo further transglutaminase-catalyzed attachment to other reactive glutaminyl residues to yield bis-(gamma-glutamyl)polyamine cross-bridges. This essay considers mechanistic features of these reactions as catalyzed by various forms of transglutaminases present either extracellularly or intracellularly in mammals. The potential physiological significance of the reactions in mammalian cells and body fluids is discussed.