Engineering cytochromes for photocatalysis: Biohybrid assemblies for light-driven dye decoloration

A major challenge in developing effective photocatalysts lies in engineering the efficient coupling of one-electron photochemistry with the multi-electron requirements of chemical transformations. Here we demonstrate biohybrid assemblies that achieve this key performance requirement by storing photoenergized electrons on multiple heme cofactors within the MtrC enzyme which catalyzes azo dye reduction. The biohybrid assemblies were created by site-selective labeling of MtrC with a Ru(II) (bipyridine)₃ photosensitizer dye. Photocatalytic azo dye reduction and decoloration occurred when these assemblies were irradiated in the presence of a sacrificial electron donor. Our Ru(II) (bipyridine)₃-MtrC biohybrid assemblies operate in a manner analogous to Ru(II) (bipyridine)₃-sensitized TiO₂ in the sense that photoenergized electrons accumulate in the MtrC heme chain rather than in the TiO₂ conduction band prior to driving reductive chemical transformations. We anticipate that decoration of the photosensitized MtrC protein with electrocatalysts (natural or synthetic) will enable the Ru(II) (bipyridine)₃-MtrC assemblies to drive a wide range of light-driven reductive transformations. Thus, MtrC provides a natural alternative to TiO₂ materials for which the production and disposal present significant environmental and energy impacts.