Bioelectrocatalysis of Sulfite Dehydrogenase from Sinorhizobium meliloti with Its Physiological Cytochrome Electron Partner

Abstract

We demonstrate electrochemically driven catalytic voltammetry of the Mo‐dependent sulfite dehydrogenase (SorT) from the α‐Proteobacterium Sinorhizobium meliloti with its physiological electron acceptor, the c‐type cytochrome (SorU), with both proteins co‐adsorbed on a chemically modified Au working electrode. Both SorT and SorU were constrained under a perm‐selective dialysis membrane with the biopolymer chitosan as a co‐adsorbate, while the electrode was modified with a 3‐mercaptopropionate self‐assembled monolayer cast on the Au electrode. Cyclic voltammetry of the SorU protein reveals a well‐defined quasireversible FeIII/II redox couple at +130 mV versus NHE in 100 mM phosphate buffer solution (pH 7.0). Introduction of wild‐type sulfite dehydrogenase (SorTWT) and sulfite transforms this transient SorU voltammetric response into a sigmoidal catalytic wave, which increases with sulfite concentration before eventually saturating. In addition to the wild‐type enzyme, the variants SorTR78K, SorTR78M, and SorTR78Q were also examined electrochemically in an effort to better understand the role of amino acid residue Arg78, which is in the vicinity of the Mo active site of SorT.

Electrocatalysis of a Europium‐Dependent Bacterial Methanol Dehydrogenase with Its Physiological Electron‐Acceptor Cytochrome cGJ

“…However, the redox response at +255 mV was greatly enhanced when 0.25 % chitosan solution was co‐adsorbed with the protein at the same electrode surface (Figure b). A similar phenomenon was reported for other proteins such as the c ‐type cytochrome (SorU) from Sinorhizobium meliloti , human cytochrome b 5 and the heme cofactor within human sulfite oxidase at carboxylate‐terminated self‐assembled monolayer‐modified Au electrodes. The exact nature of the Au/MU‐chitosan–cytochrome c GJ interaction is not known but it evidently stabilizes non‐covalent interactions, principally H‐bonding, that keep cytochrome c GJ in proximity of the electrode surface whilst enabling it to reorient during redox cycling.…”

“…However,t he redoxr esponse at + 255 mV was greatly enhanced when 0.25 %c hitosans olution was co-adsorbed with the protein at the same electrode surface ( Figure 2b). As imilar phenomenon was reportedf or other proteins such as the ctype cytochrome (SorU)f rom Sinorhizobium meliloti, [22] human cytochrome b 5 [23] and the heme cofactor within human sulfite oxidase [24] at carboxylate-terminated self-assembled monolay- Chem. Eur.J.…”

Cover Feature: Electrocatalysis of a Europium‐Dependent Bacterial Methanol Dehydrogenase with Its Physiological Electron‐Acceptor Cytochrome cGJ (Chem. Eur. J. 37/2019)

“…However,t he redoxr esponse at + 255 mV was greatly enhanced when 0.25 %c hitosans olution was co-adsorbed with the protein at the same electrode surface (Figure 2b). As imilar phenomenon was reportedf or other proteins such as the ctype cytochrome (SorU)f rom Sinorhizobium meliloti, [22] human cytochrome b 5 [23] and the heme cofactor within human sulfite oxidase [24] at carboxylate-terminated self-assembled monolay- er-modified Au electrodes. The exact nature of the Au/MU-chitosan-cytochrome c GJ interaction is not known but it evidently stabilizes non-covalent interactions, principally H-bonding, that keep cytochrome c GJ in proximity of the electrode surface whilst enabling it to reorient during redox cycling.…”

Recent Progress in the Development of Advanced Functionalized Electrodes for Oxygen Evolution Reaction: An Overview

“…In general, transition metals are tremendously used as electrode materials for many applications [ 59 , 60 , 61 ]. This is because they are highly conductive due to the presence of multiple oxidation states, provide excellent redox properties and the proton is easily inserted or removed into the crystal lattice through the reduction-oxidation process.…”