Tuning the Catalytic Bias of Hydrogenase Enzymes
Hydrogenase enzymes catalyze the seemingly simple interconversion of protons and electrons with hydrogen (H2) gas. These enzymes are ubiquitous in nature, being found in bacteria and archaea as well as in single-celled eukaryotes. They are important in H2 gas cycling and interspecies H2 gas transfer as well as in the energetics of many microbial systems.
The unifying feature of all hydrogenases of the [FeFe]-type is a complex and unique metallocluster termed the “H-cluster.” The H-cluster contains a conventional cubane [4Fe-4S] subcluster that is bridged through a cysteinyl thiolate to a unique 2Fe subcluster having carbon monoxide, cyanide, and azadithiolate ligands.
A group of researchers at Washington State University, in collaboration with Stanford Synchrotron Radiation Lightsource X-ray macromolecular crystallography (MX) scientists, solved several hydrogenase structures from Clostridium pasteurianum to very high resolution using beam line12-2 and found dual conformations of residues near the H-cluster. X-ray free-electron laser (XFEL) data were also collected at the Linac Coherent Light Source X-ray Pump Probe station, which provided evidence that the different conformations represented different oxidation states.
Together with electrochemical, spectroscopic and theoretical calculations, the group found that key amino acids within the H-cluster adopted different conformations as a function of oxidation state. This structural flexibility makes it possible to modulate the properties of the electronic structure of the H-cluster via secondary, noncovalent interactions. The researchers propose that the dynamic changes observed in C. pasteurianum are important for imposing a neutral catalytic bias or an efficacy in catalyzing both H2 oxidation and proton reduction at similar rates.
Artz, J. H., et al. 2020. “Tuning Catalytic Bias of Hydrogen Gas Producing Hydrogenases,” Journal of the American Chemical Society 142(3), 1227–35. [DOI:10.1021/jacs.9b08756]