Optimizing Photoactive Proteins for Optoelectronic Environments by Using Directed Evolution

Genetic engineering has recently emerged as a popular tool for tailoring biological macromolecules to function in nonnative environments. Most protein optimization efforts have advanced in large part as a result of significant advances in the methods and procedures of genetic engineering, most notably, directed evolution. Directed evolution mimics natural selection by combining techniques in genetic modification with differential selection. Most protein engineering research focuses on improving the thermal and chemical properties of enzymatic proteins for pharmaceutical applications. However, the recent emergence of nanobiotechnology has led researchers to broaden the scope of directed evolution. This chapter describes a strategy for tailoring the electronic and photochemical properties of proteins for performance in device applications. Among the many photoactive proteins found in nature, bacteriorhodopsin and its eubacterial counterpart, proteorhodopsin, are two leading candidates for protein-based device applications. The intrinsic stability, branched photochemistry, and photovoltaic properties of bacteriorhodopsin and proteorhodopsin make both proteins excellent candidates for three-dimensional volumetric memories, real-time holographic media, protein-based semiconductor devices, and artificial retinas.