SPECIMEN - Spectroscopic Investigation into the Mechanisms of Electron Bifurcation in [FeFe]-Hydrogenase for Green Catalysis Solutions

Improving solar fuel generating technologies and industrial catalysts are two essential aspects of tackling the ever-increasing issue of climate change. Electron bifurcating enzymes are systems which provide a blueprint to tackle both of these areas.

SPECIMEN sets out to elucidate the catalytic mechanisms and electron transfer pathways in the electron bifurcating [FeFe]-hydrogenase HydABC from Thermatoga maritima (Tm) via a combination of advanced CW/pulsed electron paramagnetic resonance (EPR) spectroscopies paired with state-of-the-art spectro-electrochemistry (SEC) and biochemical techniques.

These advanced physical characterisation techniques, tightly coupled with biochemical methods for manipulating and tailoring samples, provide the most advanced toolkit for identifying and interrogating enzymatic electron transfer pathways, and the key structural/chemical factors that govern their involvement in electron bifurcation.

The 44 FeS clusters and four flavin mononucleotide (FMN) sites of HydABC will be exploited to understand the electron bifurcating mechanism in the enzyme.

Firstly, the role of FMN in electron bifurcation will be determined by hyperfine spectroscopy (ESEEM, HYSCORE, ENDOR, EDNMR and THYCOS), which will distinguish between the type of FMN radical produced (neutral vs. anionic), elucidating the mechanism.

Next, these hyperfine techniques will be employed to investigate how the radical intermediate is stabilised by interactions with amino acid residues of the protein sequence, and the role of conformational changes in this process.

Finally, pulsed dipolar EPR spectroscopy will be used to determine how these protein conformational changes operate within the electron bifurcating mechanism, with particular emphasis on the formation of electron transfer pathways, elucidating the synergy between changes in the electronic structure of FMN and the conformation of the protein to achieve bifurcation.