Electrochemistry of a high redox potential laccase obtained by computer-guided mutagenesis combined with directed evolution

Abstract

Electrochemical characterization of the GreeDo variant of a high redox potential fungal laccase obtained by laboratory evolution together with computer-guided mutagenesis, in comparison to its parental variety (the OB-1 mutant), is presented. Both laccases, when immobilized on graphite electrodes either by direct physical adsorption or covalently attached via gold nanoparticles, were capable of both non-mediated and mediator-based bioelectroreduction of molecular oxygen at low overpotentials. GreeDo exhibited higher open circuit potential values and onset potentials for oxygen bioelectroreduction compared to OB-1. However, even though in homogeneous catalysis GreeDo outperforms OB-1 in terms of turnover numbers and catalytic efficiency, when exposed to high redox potential substrates, direct electron transfer based bioelectrocatalytic currents of GreeDo and OB-1 modified electrodes were similar. High operational stability of freely diffusing GreeDo and also the immobilized enzyme in the acidic electrolyte was registered, in agreement with high storage stability of GreeDo in acidic solutions. Keywords: Laccase, Oxygen bioelectroreduction, Direct electron transfer, Graphite electrode, Gold nanoparticles, T1 site redox potential