| Summary: | Fuel cell draws increasing attention because of its high theoretical efficiency (over 90%). However, the actual efficiency is limited by the large overpotential (500-600 mV) of the oxygen reduction reaction (ORR), which demands a potent ORR catalyst to decrease the overpotential. Towards this goal, my thesis focuses on mimicking the heme-copper oxidase and engineering a multi-copper oxidase for efficient oxygen reduction with high turnover frequency and low overpotential Heme-copper oxidases catalyze four-electron reduction of oxygen to water, and the energy harvested is utilized to drive the synthesis of adenosine triphosphate. While much effort has been made to design a catalyst mimicking the function of terminal oxidases, most biomimetic catalysts have much lower activity than native oxidases. Herein we report a designed oxidase in myoglobin with an O2 reduction rate (52 s−1) comparable to that of a native cytochrome (cyt) cbb3 oxidase (50 s−1) under identical conditions. We achieved this goal by engineering more favorable electrostatic interactions between a functional oxidase model designed in sperm whale myoglobin and its native redox partner, cyt b5, resulting in a 400-fold electron transfer (ET) rate enhancement. Achieving high activity equivalent to that of native enzymes in a designed metalloenzyme offers deeper insight into the roles of tunable processes such as ET in oxidase activity and enzymatic function and may extend into applications such as more efficient oxygen reduction reaction catalysts for biofuel cells. The other system we studied is a multi-copper oxidase called small laccase (SLAC), which consists of a catalytic trinuclear copper center (TNC) and a Type 1 (T1) Cu center for electron transfer. However, the ORR overpotential of SLAC is relatively high (400 mV) because of the lower reduction potential (Eo') of the T1 Cu (370 mV) compared to fungal laccases (780 mV). Built upon our previous success in tuning reduction potentials of T1 Cu protein azurin, we have made significant progress in ...
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