Transglutaminase catalyzed dissociation and association of protein-polyamine complex

Transglutaminase 2 (TG2) has been reported to be involved in cell growth through the formation of epsilon-(gamma-glutamyl) lysine (Gln-Lys) or N-(gamma-glutamyl) polyamine (Gln-polyamine). We have recently reported that the inhibition of Gln-Lys cross-linking by the formation of Gln-spermidine led to the increase of DNA synthesis in regenerating rat liver. TG2 may catalyze the replacement reaction between Lys residues in protein and polyamines. In the present study, we attempted to develop an experimental model for ascertaining this replacement reaction. We examined whether or not TG2 exhibited the association and dissociation reaction of Gln-polyamine bond in protein, using N,N-dimethylcasein (DC). The dissociated polyamines were identified by autoradiography. The dissociation of [(14)C] polyamines from DC bond [(14)C] polyamines complex by TG2 could occur in the presence of non-radioactive polyamines as second amine donor, whereas in the absence, could not almost occur. Moreover, it was indicated that this release of old [(14)C] polyamine bonded to DC was due to binding of added new [(14)C] polyamine to Gln residues in DC. These results demonstrate that TG2 catalyzes the replacement reaction between added [(14)C] polyamine and DC bond [(14)C] polyamine. The dissociation and association reaction may both occur together, the new DC-polyamine complex being formed at the same time as the dissociation of old DC-polyamine complex, since readying a second amine donor is necessary to dissociate DC-polyamine complex. These results indicate that this experimental model is successful in the study of TG2-catalyzed dissociation and association reaction of Gln-polyamine bond in protein.