Correspondence on "Fortification of FeS Clusters Reshapes Anaerobic CO Dehydrogenase into an Air-Viable Enzyme ThroughMultilayered Sealing of O2 Tunnels"

In their recent communication in Angewandte Chemie (10.1002/anie.202508565), Suk Min Kim and coworkers have described the effect of modifying the gas channels of the CO dehydrogenase II from Carboxydothermus hydrogenoformans, an enzyme that oxidizes reversibly CO into CO2. Their goal was to use mutagenesis to slow down the arrival of O2 at the active site. They reported a large increase in the resistance against oxygen, one of the major barriers to the application of this extremely fast and efficient enzyme in biotechnological devices, with an increase in the IC50 of more than two orders of magnitudes for some variants, with only a minor impact on the affinity of the enzyme for CO. We have produced the same variants, and characterized them in depth using Protein Film Electrochemistry. We used an approach that has proven very useful to learn and understand about the reactivity of CO dehydrogenases (and other redox enzymes like hydrogenases) with O2. We found that, contrary to the claims by Kim and coworkers, the A559W and the A559W/V610H mutants are not more resistant than the WT against oxygen.