Abstract text (incl. figure legends and references)
The prototypical hydrogen producing enzyme, the membrane-bound formate hydrogenlyase (FHL) complex from Escherichia coli, catalyzes the conversion of formate to CO2 and H2 under anaerobic fermentative conditions. The enzyme is long known to share sequence homology with respiratory complex I, but an energy conserving character of FHL remains elusive.
We aim to get a better understanding of the FHL complex and the role it plays in bacterial bioenergetics by combining high-resolution electron cryo-microscopy (cryo-EM) with complementary biophysical methods.
Our cryo-EM structures reached resolutions of up to 2.6 Å and revealed important differences and similarities between FHL and complex I. We analyzed possible substrate proton pathways to the [NiFe] active site, which may play an important role in the mechanism of the enzyme. Furthermore, we identified an unpredicted metal-ion, which could play a regulatory role in binding the loosely attached formate dehydrogenase component.
Since FHL is an ancestor of respiratory complex I understanding its function on a molecular level sheds light on the evolution of energy conservation from early to modern life.