Electrostatic-Driven Activity, Loading, Dynamics, and Stability of a Redox Enzyme on Functionalized-Gold Electrodes for Bioelectrocatalysis

The oxygen reduction reaction is the limiting step in fuel cells, and many works are in progress to find efficient cathode catalysts. Among them, bilirubin oxidases are copper-based enzymes that reduce oxygen into water with low overpotentials. The factors that ensure electrocatalytic efficiency of the enzyme in the immobilized state are not well understood, however. In this work, we use a multiple methodological approach on a wide range of pH values for protein adsorption and electrocatalysis to demonstrate the effect of electrostatic interactions on the electrical wiring, dynamics, and stability of a bilirubin oxidase adsorbed on self-assembled-monolayers on gold. We show on one hand that the global charge of the enzyme controls the loading on the interface and that the specific activity of the immobilized enzyme decreases with the enzyme coverage. On the other hand, we show that the dipole moment of the protein and the charge in the vicinity of the Cu site acting as the entry point of electrons drive the enzyme orientation. In case of weak electrostatic interactions, we demonstrate that local pH variation affects the electron transfer rate as a result of protein mobility on the surface. On the contrary, stronger electrostatic interactions destabilize the protein structure and affect the stability of the catalytic signal. These data illustrate the interplay between immobilized protein dynamics and local environment that control the efficiency of bioelectrocatalysis

Enhanced oxygen-tolerance of the full heterotrimeric membrane-bound [NiFe]-hydrogenase of ralstonia eutropha.

Hydrogenases are oxygen-sensitive enzymes that catalyze the conversion between protons and hydrogen. Water-soluble subcomplexes of membrane-bound [NiFe]-hydrogenases (MBH) have been extensively studied for applications in hydrogen-oxygen fuel cells as they are relatively tolerant to oxygen, although even these catalysts are still inactivated in oxidative conditions. Here, the full heterotrimeric MBH of Ralstonia eutropha, including the membrane-integral cytochrome b subunit, was investigated electrochemically using electrodes modified with planar tethered bilayer lipid membranes (tBLM). Cyclic voltammetry and chronoamperometry experiments show that MBH, in equilibrium with the quinone pool in the tBLM, does not anaerobically inactivate under oxidative redox conditions. In aerobic environments, the MBH is reversibly inactivated by O2, but reactivation was found to be fast even under oxidative redox conditions. This enhanced resistance to inactivation is ascribed to the oligomeric state of MBH in the lipid membrane

Biohydrogène : Stratégies d'immobilisation d'hydrogénases sur électrodes

International audienc

Biohydrogen : hydrogenases immobilisation strategies

International audienc

Recent advances in surface chemistry of electrodes to promote direct enzymatic bioelectrocatalysis

International audienceRedox enzymes catalyze major reactions in microorganisms to supply energy for life. Their use in electrochemical biodevices requires their integration on electrodes, while maintaining their activity and optimizing their stability. In return, such applicative development puts forward the knowledge on involved catalytic mechanisms, providing a direct electrode connection of the enzyme is fulfilled. Enzymes being large molecules with active site embedded in an insulating moiety, direct bioelectrocatalysis supposes strategies for specific orientation of the enzyme to be developed. In this review, we summarize recent advances during the past three years in the chemical modification of electrodes favoring direct electrocatalysis. We present the different methodologies used according to the electrode materials, including metals, carbon-based electrodes or porous structures, and discuss the gained insights into bioelectrocatalysis. We especially focus on enzyme engineering which appears as an emerging strategy for enzyme anchoring. Remaining challenges will be discussed with regards to these last findings

New trends in enzyme immobilization at nanostructured interfaces for efficient electrocatalysis in biofuel cells

International audienceBiofuel cells, and among them enzymatic biofuel cells, are expected to take part in a sustainable economy in a next future. The development of such biodevices requires significant improvements in terms of efficiency of enzyme immobilization at the electrodes, so as to enable direct electron transfer, and to increase and stabilize the current densities. Many works during the last years aimed at reaching higher current densities, thus power densities, while increasing the long term stability of the enzymatic bioelectrodes. Search for new enzymes, wild type or mutants, new entrapment procedures, but also new electrode architectures, have been targeted. This review focuses on the materials developed and involved during the last few years to meet these demands via nanostructuration of electrode interfaces. Discussion is essentially focused on cases where direct electron transfer between enzymes and electrochemical interfaces are involved. After having introduced the main reasons for the need of nanostructuration, the materials and methods that are newly developed are described. The consequences on improved performances for enzymatic bioelectrodes are discussed, and finally major challenges for future research are addressed

Recent developments in high surface area bioelectrodes for enzymatic fuel cells

International audienceEnzymatic fuel cells (EFC) function in a similar way to low temperature proton exchange membrane fuel cells (PEMFC) but use enzymes instead of noble metals as catalysts for fuel and oxidant transformation. The need for EFCs that deliver enhanced power has resulted in high surface/volume ratio conductive materials being considered as enzyme host matrices. While the enhanced surface has effectively led to higher catalytic currents, the use of high surface area nanomaterials (HSM) has also induced new issues related to the wiring of enzymes, the role of porosity, and the effect on stability. This review discusses the most important features reported in this area over the past three years, and proposes future directions concerning EFC applications. Recent developments in high surface area bioelectrodes for enzymatic fuel cells. Available from: https://www.researchgate.net/publication/318305120_Recent_developments_in_high_surface_area_bioelectrodes_for_enzymatic_fuel_cells [accessed Jul 19, 2017]

Electrochemical study of the intermolecular electron transfer to Pseudomonas aeruginosa cytochrome cd1 nitrite reductase

The kinetics of electron transfer reaction between cytochrome cd(1) nitrite reductase (NiR) from Pseudomonas aeruginosa and various physiological/non physiological redox partners was investigated using cyclic voltammetry at the pyrolytic graphite electrode. While NiR did not exchange electron with the electrode, cytochrome c(551) and azurin, both from Ps. aeruginosa, behaved as fast electrochemical systems. The intermolecular electron transfers between NiR and cytochrome c(551) or azurin as electron shuttles, in the presence of nitrite, were studied. Second order rate constants of 2 x 10(6) and 1.4 x 10(5) M-1 s(-1) are calculated for cytochrome c(551) and azurin, respectively. The dependence of the second-order rate constant on ionic strength and pH is discussed. Finally, the effect of the global charge of the electron shuttles was explored using differently charged species (proteins or small ions). The experimental results suggest involvement of polar interactions as well as of hydrophobic contacts in the protein recognition prior to the intermolecular electron transfer. As the cross-reaction between Ps. nautica cytochrome c(552) and Ps. aeruginosa NiR was shown to be as efficient as the catalytic reaction involving the physiological partners, it is concluded to a 'pseudo-specificity' in the recognition between NiR and the electron donor