Synthesis of Uniform Protein−Polymer Conjugates

We have developed a novel technique to synthesize near-uniform protein−polymer conjugates by initiating atom transfer radical polymerization of monomethoxy poly(ethylene glycol)−methacrylate from 2-bromoisobutyramide derivatives of chymotrypsin (a protein−initiator). Polymerization initiated from the monosubstituted protein−initiator resulted in the conjugate containing a single, near-monodisperse polymer chain per protein molecule with polydispersity index 1.05. Increasing the number of conjugated 2-bromoisobutyramide initiators per molecule of protein increased the molecular weights and polydispersity indices of the final protein−polymer conjugates. The generic nature of this technique was demonstrated by initiating polymerization of nonionic, cationic, and anionic monomers from the protein−initiator. Protein−polymer conjugates synthesized by this novel technique retained 50−86% of the original enzyme activity. The technique described herein should be useful in synthesizing well-defined protein−polymer conjugates exhibiting a wide range of physical and chemical properties.