Modular Genetic Code Expansion Platform and PISA Yield Well-Defined Protein-Polymer Assemblies

We present a modular platform from which biohybrid protein-polymer nanostructures can be generated in a straightforward and facile manner. Specifically, an aqueous polymerization-induced self-assembly (PISA) AB block copolymerization system was derived from a mutant superfolder green fluorescent protein (sfGFP) as the solvophilic, stabilizing A block. By genetically encoding sfGFP with an isobutyryl bromide functionality, we grafted a quintessential atom-transfer radical polymerization initiation site with hydroxypropyl methacrylate (HPMA) to form the solvophobic B block. Monitoring nanostructure formation using dynamic light scattering, gel permeation chromatography, and transmission electron microscopy revealed uniform micellar morphologies. The radii of the micelles increased with increasing HPMA block length, resulting in nanoparticle sizes ranging from 15 to 48 nm. Solvophilic stabilization afforded by the encoded sfGFP makes this an ideal PISA initiator, and we posit this platform has potential for generating complex biohybrid nanostructures for other protein-polymer systems.