Effects of Elimination of a Helix Regions on Direct Electron Transfer-type Bioelectrocatalytic Properties of Copper Efflux Oxidase

We investigated properties of direct electron transfer (DET)-type bioelectrocatalysis of recombinant native Copper efflux oxidase (rCueO) and its variants which lack a helices covering the electron-donating substrate-binding site (Delta alpha 5-7CueO, Delta alpha 5CueO, Delta alpha 6-7CueO, and Delta alpha 5-7+1/2 alpha 5CueO) at mesoporous carbon electrodes without pretreatment and modified with positively or negatively charged aromatic amines. Kinetic and thermodynamic parameters of the electrode reaction were obtained by analysis of steady-state catalytic waves based on a random orientation model and examined the results on the basis of the structural information of the enzymes. The data suggested that the electron transfer pathway is different from that in solution; electrons are transferred from an electrode to the T1 Cu site through the negatively charged position near the T1 Cu site in rCueO without passing through the a helix region in DET-type bioelectrocatalysis. Positively charged electrode was a suitable scaffold for DET-type reaction of rCueO. The T1 Cu site in Delta alpha 5CueO became somewhat hydrophobic and hydrophobic electrode worked as a suitable scaffold for the variant. Negatively charged electrode seems to induce unfavorable attractive orientation for DET-type reaction between the electrode and positively charged region of the CueOs on the opposite side of the T1 Cu site. (C) The Author(s) 2020. Published by ECSJ.