Research: Project 2
Unraveling the secrets of biological H2 production.
H2 is an attractive alternative to traditional fossil fuels because it has a very high energy content per unit weight and releases only energy and water when burned. Unfortunately, approximately 95% of the H2 produced commercially is derived from fossil fuels, and it is therefore neither environmentally friendly nor renewable. Many microorganisms, however, produce H2 naturally, often using enzymes known as hydrogenases. In particular, H2 generated by oxygenic phototrophs holds special promise because water is the substrate and the energy required for H2 production is derived from light.
Hydrogenases are found in a diverse array of microorganisms, and they are separated into three subclasses based on the composition of their active sites: [FeFe]-, [NiFe]-, and [Fe]-hydrogenases. [FeFe]- hydrogenases in particular have garnered significant interest because they are among the most efficient H2-producing catalysts known. The active site of [FeFe]- hydrogenases consists of an unusual dinuclear iron center coordinated to CO, CN-, and a five-atom dithiolate. Although considerable progress has been made in elucidating the structure and assembly of the catalytic site, relatively little effort has focused on the mechanism by which electrons and protons are transferred to the active site.
We are particularly interested in the intramolecular transport of substrates. Proton transfer is an essential component of H2 production, and we recently identified four amino acid residues that form a proton pathway between the active site and the enzyme surface. Furthermore, many bacterial [FeFe]- hydrogenases appear to contain a branched electron transport pathway, and experiments in our lab are designed to elucidate the role of these two different pathways. Additional unresolved questions include the mechanism by which electron and proton transfer are coupled as well as ideal strategies for engineering a robust microorganism to serve as an H2 production factory.