Protein-engineering improvement of direct electron transfer-type bioelectrocatalytic properties of D-fructose dehydrogenase

Abstract

D-Fructose dehydrogenase (FDH) contains a flavin adenine dinucleotide (FAD) in subunit I and three heme c moieties (1c, 2c, and 3c from the N-terminus) as the electron transfer relaying sites. The electron transfer in direct electron transfer-type bioelectrocatalysis of FDH is proposed to proceed in sequence from FAD, through heme 3c, to heme 2c without going through heme 1c. In order to improve the performance of the bioelectrocatalysis, we constructed a variant (M450QΔ1cFDH) in which 143 amino acid residues involving heme 1c were removed and M450 as the sixth axial ligand of heme 2c was replaced with glutamine to negatively shift the formal potential of heme 2c. The M450QΔ1cFDH variant was adsorbed on a planar gold electrode. The variant-adsorbed electrode produced a clear sigmoidal steady-state catalytic wave of fructose oxidation in cyclic voltammetry. The limiting current density was 1.4 times larger than that of the recombinant (native) FDH. The half-wave potential of the wave shifted by 0.2 V to the negative direction. M450QΔ1cFDH adsorbed rather homogeneously in orientations suitable for DET-type bioelectrocatalysis.