Tailoring Site Specificity of Bioconjugation Using Step-Wise Atom-Transfer Radical Polymerization on Proteins.

Protein-polymer conjugates are powerful combinations of the biotic and abiotic worlds that impact many industries. Predicting the site and impact of polymer growth from the surface of proteins is only useful if we can use that information to choose which site to modify synthetically. We have explored the combination of a predictive algorithm with a unique stepwise atom-transfer radical polymerization (ATRP) to selectively move the predominant modification sites around a model enzyme. Lysozyme was modified with defined stoichiometric ratios of polymerization initiators and initiation inhibitors to selectively and strategically grow poly(carboxybetaine methacrylate) polymers from different protein sites. Electrospray ionization mass spectrometry was used to examine the uniformity of the lysozyme-initiator and lysozyme-inhibitor complexes prior to polymer growth. Bioactivity of the lysozyme-polymer conjugates was examined as a function of polymer location on the enzyme surface. Step-wise atom-transfer radical polymerization from proteins provides a versatile and modular approach that can be extended to the rational and selective design of other protein-polymer conjugates.