Azurin is a Type 1 copper protein that displays a strong blue color, moderately high reduction potential (E°′; 265 mV vs. SHE) and very efficient electron transfer (ET) properties. Its small size and rigid structure makes azurin an ideal protein to investigate and understand structural features responsible for fine-tuning its electronic properties that are responsible for its colors, as well as its functional properties such as E°′ and ET rates. For example, by changing residues in the secondary coordination spheres that are responsible for either hydrophobicity or hydrogen bonding interactions with the conserved Cys that is coordinated to the copper center, we have been able to engineer azurins that cover the entire physiological available E°′ range (from −954 mV to +970 mV vs. SHE) [1] and display one of the lowest reorganization energy [2] and Marcus inverted region for ET [3]. In addition, our ability of to tune its E°′ has made it possible for us to transform azurin from a blue copper center that performs ET function into a red copper center that exhibits enzymatic activity such as reversible S-nitrosylation [4]. The fast, efficient and reversible S-nitrosylation reaction is used to demonstrate its ability to prevent NO inhibition of cytochrome bo3 oxidase activity by competing for NO binding with the native enzyme under physiologically relevant conditions. The knowledge gained from the study of these azurins with different colors and functional properties has laid a strong foundation for designing metalloenzymes that can catalyze reactions with close to zero overpotential.

RGB copper azurins: Engineered azurins that display a wide range of colors, reduction potentials and enzymatic activities

254th National Meeting (2017)

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