(620t) Synthesis of Well-Defined Protein-Polymer Conjugates Using Ligase-Mediated Site-Specific Modification and RAFT Polymerization

Advances in materials synthesis using proteins have allowed for the preparation of a variety of protein-polymer materials that find numerous applications in medicine, synthesis, and environmental monitoring.  Protein-polymer conjugates, or bioconjugates, may be designed with linear and branched hydrophilic polymer such as PEG or may be combined with hydrophobic or crosslinked polymers resulting in insoluble supports in the form of gels, foams, fibers, wipes, and coatings.  Synthesis of protein-polymer materials involves attachment of polymer chains or initiators for polymer synthesis to the reactive functionalities on the enzyme.  Typically, protein modification approaches provide little control over the number and location of modification sites on the protein surface.  Approaches that allow site-specific and bioorthogonal chemical modification of proteins are needed for the design of well-defined protein-polymer conjugates.  We have used a novel approach to incorporate bioorthogonal reactive handles for site-specific protein modification that uses ligase-mediated post-translational modifications. This approach uses the enzyme lipoic acid ligase (LplA) to modify a protein, which contains a unique peptide tag (LAP), with clickable azide groups that may then serve as sites for polymer attachment.  In this work we investigate the potential utility of designing uniform protein-polymer conjugates using the LAP/LplA system and RAFT polymerization.  We have synthesized an alkyne terminated chain transfer agent; however, to improve the solubility of this RAFT agent a short macro-CTA of acrylamide was grown in solvent first.  The macro-CTA was subsequently conjugated to the ligated GFP in a buffer solution using the copper catalyzed click reaction.  The macro-CTA GFP conjugates were chain extended with functional monomers to create a library of bioconjugates with different insertion sites, chain lengths and chemical functionalities.  These bioconjugates were characterized to determine the number CTA of attachments, polymer length, and stability.