Electrochemical analysis of autodisplayed adrenodoxin (Adx) on the outer membrane of E. coli

In this work, adrenodoxin (Adx) was expressed on the outer membrane of E. coli by autodisplay and then the iron–sulfur cluster was incorporated into apo-Adx by an anaerobic reconstitution process. For the determination of the redox potentials of the iron–sulfur clusters of the autodisplayed Adx, E. coli cells with autodisplayed Adx were immobilized on a gold electrode modified with a self-assembled monolayer of mercaptoundecanoic acid (MUA). From the repeated cyclic voltammetry (CV) analysis, the E. coli (10 mM HEPES buffer, pH 7.0) with autodisplayed Adx showed significant changes in shape with an oxidation peak at + 0.4 V (vs. Ag/AgCl) and a reduction peak at − 0.3 V (vs. Ag/AgCl) after the reconstitution process for the incorporation of the iron–sulfur cluster. From the repeated CV analysis in the reduction and oxidation potential ranges, the iron–sulfur clusters of the autodisplayed Adx were observed to undergo reversible redox reactions via direct electron transfer to the MUA-modified gold electrode.