Postdoctoral Research - Protein-Polymer Biocatalysts
Proteins comprise one of the most impressive categories of polymers known: they produce extremely strong and tough materials, they efficiently catalyze chemical transformations, they selectively bind analytes within complex mixtures, and they harvest light by converting it into chemical energy. By combining the incredible diversity of structure and function of proteins with the stability, chemical diversity, and processability of synthetic polymers, materials with the advantages of both components can be accessed. In order to use proteins as sensors, biofuel cells, or industrial catalysts the protein-based material must maintain mechanical integrity, protein stability and longevity, and access to the protein active site. The self-assembly of proteins in solid-state materials has the ability to achieve each of these requirements.
Two methods for the self-assembly of protein biocatalysts were explored, both relying on the ability of block copolymers to direct self-assembly. First, synthesis of a protein-polymer block copolymer was achieved by site-specific functionalization of cytochrome P450 BM3 with poly(N-isopropylacrylamide). The polymer modified protein generates a material that can be easily processed to create a self-assembled heterogeneous biocatalyst. The self-assembly of the bioconjugate in concentrated solutions was characterized by small-angle x-ray scattering (SAXS) and depolarized light scattering (DPLS). The thin film nanostructure was also investigated by grazing-incidence small-angle x-ray scattering (GISAXS). Catalytic activity of the thin films for C-H oxidation was measured using a variety of substrates.
An additional method for controlling the self-assembly of proteins was probed. Non-specific modification of proteins to vary their surface charge was also examined as a means for directing protein self-assembly. Using model proteins and lysine succinylation, a panel of proteins with varying charge density was synthesized. The ability of these proteins to form complex coacervates with oppositely charged polyelectrolytes was studied in order to identify parameters that governed complex coacervation of proteins. The fundamental parameters uncovered allow any protein of interest to be successfully modified to enable complex coacervation. These findings were applied to the synthesis of complex coacervate core micelles with protein cores. Encapsulation of P450 enzymes in these ionic micelles enables their use as biocatalysts for C-H oxidation.