Responsive polymer-protein bioconjugates prepared by RAFT polymerization and copper-catalyzed azide-alkyne click chemistry

Responsive polymer-protein conjugates were synthesized by combination of reversible addition-fragmentation chain transfer (RAFT) polymerization and a grafting-to approach by a highly efficient click chemistry strategy. A model protein, bovine serum albumin (BSA), was functionalized with an alkyne moiety by reaction of its free cysteine residue with propargyl maleimide. Azido-terminated poly(N-isopropylacrylamide) (PNIPAM-N-3) was prepared via RAFT, and polymer-protein coupling was accomplished by copper-catalyzed azide-alkyne cycloaddition. In aqueous solution, the conjugates were observed by dynamic light scattering to be larger than the free polymer or the unmodified protein. Upon heating above the PNIPAM lower critical solution temperature (LICST), the PNIPAM-BSA bioconjugates formed stable nanoparticles composed of dehydrated polymer and hydrophilic protein.