Protein and Metabolic Engineering
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Development of Whole-Cell Biocatalysts
Heterogeneous biocatalysis has been studied numerous times as a means of stabilizing an enzyme, and increasing its recyclability from solution. Most often, the support particles for immobilization have been solid-phase supports such as silica particles, gold nanoparticles, or carbon nanotubes. While these systems are effective, they require protein to first be purified before immobilization can be performed. Whole-cell biocatalysis is a method by which the cell that expresses the enzyme becomes the carrier particle itself. This eliminates the need for protein purification which is expensive and time-consuming. Whole-cell biocatalysts can be created via periplasmic expression, cell surface display, or even regular cytosolic expression depending on the substrate being targeted. Another advantage is that these catalysts are easily renewable simply by culturing more cells harboring the necessary recombinant genes.
Currently, we are developing whole-cell biocatalysts for CO2 hydration. Carbon fixation is a very slow process when left uncatalyzed yet is necessary for many different reactions, both physiologically and industrially. Thus, carbonic anhydrase is used to accelerate the rate of CO2 hydration to bicarbonate and carbonate ions. Applications for this technology include carbon capture and storage, biofuel production, and electrochemical biosensors. Our catalysts are created by periplasmically expressing carbonic anhydrase in E. coli. Development of these catalysts includes determining the best periplasmic expression system, modifications to the cell to enhance permeability to the substrate and reactant, and characterizing the lifetime of the catalysts as a design parameter for industrial applications.