Genetic optimization and characterization of retinylidene proteins for performance in devices

Retinylidene proteins are integral membrane proteins composed of seven transmembrane helical domains with an all-trans retinal covalently linked to the protein via a conserved lysine residue. This thesis focuses on the photochemical optimization of bacteriorhodopsin for performance in a wide variety of optoelectronic devices. The thesis begins with a detailed discussion of the structure, function and spectral tuning properties of the prokaryotic retinal-binding proteins, bacteriorhodopsin and proteorhodopsin. The mechanisms of spectral tuning in the green-absorbing form of proteorhodopsin are explored by using homology modeling and molecular orbital theory calculation. The stability of BR- and SRII-based GPR model was studied in terms of its potential energy, relative stability and pH dependence properties. Orientation of the guanidinium side chain of arginine 94 and the role of the imidazole moiety of histidine 75 are investigated in detail. Genetic optimization of bacteriorhodopsin results in the generation of BR variants with enhanced M and O state photokinetics. The V49A BR variant exhibits enhanced thermal and photokinetic properties. The V49A protein forms the photostationary Q state efficiently following red light irradiation. The superior characteristics of the BR variant make the variant an ideal candidate for 3D memory. A double BR variant with a long-lived M state photointermediate is identified using time-resolved experiments. The double variant with lengthened M state yield has potential in holography.