[SCAN] Towards a Hydrogen-based energy paradigm: Improving the O2 tolerance of a [NiFeSe] hydrogenase

Title: Towards a Hydrogen-based energy paradigm: Improving the O2 tolerance of a [NiFeSe] hydrogenase

Speaker: Pedro Matias

Affiliation: Industry and Medicine Applied Crystallography 

Abstract: Rising CO2 emissions and the depletion of fossil fuel reserves are a global concern. Automobiles powered by internal combustion engines (especially diesel) also produce nitrogen oxides (NOx) which are a known health concern. Hydrogen has long been considered an attractive energy vector for reducing global CO2/NOx emissions. However, current H2/O2 fuel cells require the expensive rare metal Pt as electrode materials and hydrogen is mostly obtained from fossil fuels.

Some living organisms use or produce hydrogen in their metabolic processes through specialized enzymes, Hydrogenases (Hases), which catalyze the reversible oxidation of the H2 molecule. Hases are therefore good candidates for using hydrogen as an energy vector in an economic paradigm based on renewable sources, either for applications in H2/O2 fuel cells, replacing Pt, or in devices for H2 production. Hases are classified according to the metals present in their active site: [NiFe], [FeFe] and [Fe]. In the catalytic site of the [NiFe] Hases, a binuclear Ni-Fe co-factor is bound to the protein chain by four cysteine residues and the Fe atom is also coordinated by three diatomic ligands (two CO and one CN). In addition, [NiFe] Hases contain several Fe-S clusters.

[NiFeSe] Hases are a [NiFe] subclass where one of the cysteines is replaced by a selenocysteine residue. The [NiFeSe] Hases are specially interesting for use in biotechnological applications, since they are more active in both H2 production and oxidation than standard [NiFe] Hases, display less inhibition by the product H2, and most importantly have a higher degree of O2 tolerance. Nevertheless, they are also susceptible to inactivation by O2. For more than 12 years, my Lab has been collaborating with the Labs of Inês Cardoso Pereira (Bacterial Energy Metabolism) and Cláudio Soares (Protein Modeling) on biochemical, electrochemical, spectroscopic and structural studies of the [NiFeSe] Hase from the sulfate-reducing bacterium Desulfovibrio vulgaris Hildenborough (DvH).

Earlier studies allowed the identification of the structural consequences of oxidative damage to the enzyme: a reversible chemical oxidation of the Fe-S cluster closest to the active site and an irreversible oxidation to sulfinate of a cysteine residue bound to the Ni atom in the active site.

The development of a system for homologous expression of the enzyme allowed the production of variants by residue mutation, aiming to improve its O2 tolerance. Of the three such variants produced to date, two were successful in largely preventing or delaying the cysteine oxidation, and electrochemical and biochemical activity assays of these variants revealed an increase in O2 tolerance in comparison with the wild-type enzyme.

In parallel, experiments with crystals pressurized with Krypton and Oxygen gases aimed at mapping the possible gas access routes to the enzyme active site.

Zoom webinar - ITQB NOVA Virtual auditorium

https://zoom.us/j/729768442