Photochemical and Thermal Stability of Green and Blue Proteorhodopsins: Implications for Protein-Based Bioelectronic Devices

摘要

The photochemical and thermal stability of the detergent solubilized blue- and green-absorbing proteorhodpsins, BPR and GPR respectively, are investigated to determine viability of these proteins for photonic device applications. Photochemical stability is studied by using pulsed laser excitation and differential uv-vis spectroscopy to assign the photocyclicity. GPR, with a cyclicity of 7×10⁴ photocycles protein⁻¹, is 4–5 times more stable than BPR (9×10³ photocycles protein⁻¹), but is less stable than native bacteriorhodopsin (9×10⁵ photocycles protein⁻¹) or the 4-keto-bacteriorhodopsin analog (1×10⁵ photocycles protein⁻¹). The thermal stabilities are assigned by using differential scanning calorimetry and thermal bleaching experiments. Both proteorhodopsins display excellent thermal stability, with melting temperatures above 85°C, and remain photochemically stable up to 75°C. The biological relevance of our results is also discussed. The lower cyclicity of BPR is found to be adequate for the long-term biological function of the host organism at ocean depths of 50 m or more.