The microbial transglutaminase immobilization on carboxylated poly(N-isopropylacrylamide) for thermo-responsivity

• Transglutaminase was immobilized on carboxylated poly(N-isopropylacrylamide).
• The pNIPAM-mTG conjugate showed a low critical solution temperature around 39 °C.
• The pNIPAM-mTG conjugate can catalyze protein cross-linking and PEGylation in soluble form.
• The pNIPAM-mTG conjugate can be removed from reaction based on thermal transition.

Microbial transglutaminase (mTG) is widely utilized in the PEGylation of pharmaceutical proteins. mTG immobilization can be achieved via covalent bonding on solid supports. However, the catalytic efficiency of mTG immobilized on solid supports was significantly reduced by mass transfer limitation. To overcome this limitation, mTG was covalently immobilized on the thermo-responsive carboxylated poly(N-isopropylacrylamide) (pNIPAM). The pNIPAM-mTG conjugate exhibited reversibly solubility in aqueous solution with a low critical solution temperature (LCST) at 39 °C, i.e., it was insoluble above 39 °C and soluble below 39 °C. The pH dependence of the pNIPAM-mTG conjugate was similar with that of the native mTG. Upon conjugation to pNIPAM, the optimal temperature of mTG shifted down from 50–55 °C to 40–45 °C, and the thermal stability of the conjugate was elevated. The easy separation of the pNIPAM-mTG conjugate with its substrate and the catalytic efficiency of the pNIPAM-mTG conjugate were demonstrated by employing the pNIPAM-mTG conjugate to cross-link bovine serum albumin (BSA) and catalyze PEGylation of therapeutic protein, cytochrome c (Cyt C), respectively. The thermo-responsive mTG is suitable to modify proteins in food processing and biomedical engineering.