Ultimate downsizing of d-fructose dehydrogenase for improving the performance of direct electron transfer-type bioelectrocatalysis

d-Fructose dehydrogenase (FDH), a membrane-bound heterotrimeric enzyme, shows strong activity in direct electron transfer (DET)-type bioelectrocatalysis. An FDH variant (Δ1c2cFDH) which lacks 199 amino acid residues including two heme c moieties from N-terminus was constructed, and its DET-type bioelectrocatalytic performance was evaluated with cyclic voltammetry at Au planar electrodes. A DET-type catalytic current of d-fructose oxidation was clearly observed on Δ1c2cFDH-adsorbed Au electrodes. Detailed analysis of the steady-state catalytic current indicated that Δ1c2cFDH transports the electrons to the electrode via heme 3c at a more negative potential and at more improved kinetics than the recombinant (native) FDH. Keywords: Fructose dehydrogenase, Direct electron transfer, Protein engineering, Downsizing, Redox potential shif