Visualizing the gas channel of a monofunctional carbon monoxide dehydrogenase

Carbon monoxide dehydrogenase (CODH) plays an important role in the processing of the one-carbon gases carbon monoxide and carbon dioxide. In CODH enzymes, these gases are channeled to and from the Ni-Fe-S active sites using hydrophobic cavities. In this work, we investigate these gas channels in a monofunctional CODH from Desulfovibrio vulgaris, which is unusual among CODHs for its oxygen-tolerance. By pressurizing D. vulgaris CODH protein crystals with xenon and solving the structure to 2.10 angstrom resolution, we identify 12 xenon sites per CODH monomer, thereby elucidating hydrophobic gas channels. We find that D. vulgaris CODH has one gas channel that has not been experimentally validated previously in a CODH, and a second channel that is shared with Moorella thermoacetica carbon monoxide dehydrogenase/acetyl-CoA synthase (CODH/ACS). This experimental visualization of D. vulgaris CODH gas channels lays groundwork for further exploration of factors contributing to oxygen-tolerance in this CODH, as well as study of channels in other CODHs. We dedicate this publication to the memory of Dick Holm, whose early studies of the Ni-Fe-S clusters of CODH inspired us all.

Automated summary

In this study, the gas channels in a monofunctional CODH from Desulfovibrio vulgaris were investigated by pressurizing protein crystals and solving the structure. The results revealed an unvalidated gas channel and a shared channel with another CODH, which lays the groundwork for further exploration of oxygen-tolerance factors in this CODH and study of channels in other CODHs.