Electrochemical studies of FeFe-hydrogenases: mechanism and optimisation of their catalytic properties – ECCHYMOSE

FeFe-hydrogenases (H2ases) are large and complex metallo-enzymes which catalyse H2 oxidation and production at a conserved inorganic active-site, the so-called H-cluster. They are studied in various contexts, ranging from bioenergetics to inorganic catalysis, but the main motivation is certainly that both these enzymes and the knowledge we might acquire by studying them will prove useful for designing the catalysts we need to produce hydrogen from water in a clean process. Yet understanding why these enzymes cease to work under adverse conditions, and designing H2ases that are best suited for biotechnological applications, remain major challenges which we plan to tackle using a multidisciplinary approach that combines state-of-the-art electrochemistry, molecular biology, biochemistry and theoretical methods.
The current attempts to use the photosynthetic alga Chlamydomonas reinhardtii to produce H2 from water and light are hampered by the inactivation of this enzyme by the oxygen coming from photosynthetic water oxidation, and also by the fact that the H-cluster is destroyed by light in the UV-Vis range. This photodamage has hardly been characterized yet, and the problem of O2 sensitivity has not been approached by taking advantage of the fact that FeFe-H2ases isolated from various organisms react very differently with O2; yet the latter observation implies that it should be possible to use molecular biology to modify H2ases and make them more O2 tolerant, provided the molecular basis of oxygen sensitivity is understood.
We will combine direct electrochemistry and theoretical chemistry to understand the inhibition of theses enzymes by oxygen and light. Our approach is unique in that we intend to learn about the molecular determinants of inhibition by studying and comparing the properties of artificial hydrogenases and of a number of FeFe H2ases isolated from different microorganisms prepared by the two teams of biochemists and molecular biologists. (See confidential documents & summaries for details.) Recent, joint publications in JACS, Angewandte chemie, Nat. Chem. Biol. etc. show that the five teams have already collaborated very fruitfully, and preliminary results presented in the scientific document attest to the feasibility of the project.
Combining genetic engineering and appropriate electrochemical, photoelectrochemical and theoretical investigations will bring an entire set of new data that will increase greatly our understanding of the reactivity and vulnerability of these biological catalysts. It should also take us closer to the Graal of biohydrogen research: an H2-production biological catalyst that remains active both in the presence of O2 and upon strong illumination.