Stabilization of the Highly Hydrophobic Membrane Protein, Cytochrome bd Oxidase, on Metallic Surfaces for Direct Electrochemical Studies

Abstract

The cytochrome bd oxidase catalyzes the reduction of oxygen to water in bacteria and it is thus an interesting target for electrocatalytic studies and biosensor applications. The bd oxidase is completely embedded in the phospholipid membrane. In this study, the variation of the surface charge of thiol-modified gold nanoparticles, the length of the thiols and the other crucial parameters including optimal phospholipid content and type, have been performed, giving insight into the role of these factors for the optimal interaction and direct electron transfer of an integral membrane protein. Importantly, all three tested factors, the lipid type, the electrode surface charge and the thiol length mutually influenced the stability of films of the cytochrome bd oxidase. The best electrocatalytic responses were obtained on the neutral gold surface when the negatively charged phosphatidylglycerol (PG) was used and on the charged gold surface when the zwitterionic phosphatidylethanolamine (PE) was used. The advantages of the covalent binding of the membrane protein to the electrode surface over the non-covalent binding are also discussed.

Membrane Protein Modified Electrodes in Bioelectrocatalysis

“…The size of the NPs significantly affects the electron transfer rates and smaller particles reduced the requirement of overpotential for O 2 reduction activity by E. coli cytochrome bo 3 [54]. The group of Hellwig has recently studied the role of the surface charge of thiol-modified gold NPs, the length of the thiols and the effect of phospholipid composition on the interaction and DET between NP and the membrane enzyme, cytochrome bd [55]. Both cytochromes bo 3 and bd used in the aforementioned studies were isolated and stabilised in DDM buffer.…”