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

4 years ago

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

Ju-Chun Hsiao, Palraj Kalimuthu, Paul V. Bernhardt, Ulrike Kappler, Remya Purushothaman Nair

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. SorT it out: Electrochemically driven catalysis of a Mo-dependent bacterial sulfite dehydrogenase (SorT) is achieved with its physiological electron acceptor, a c-type cytochrome (SorU), acting as a mediator of electron transfer at a chemically modified Au working electrode. Inter-protein electron transfer is examined by comparing the wild-type SorT with a selection of variant forms.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/celc.201700838