Visualizing the Gas Channel of a Monofunctional Carbon Monoxide Dehydrogenase

Abstract

Carbon monoxide dehydrogenase (CODH) plays an important role in the processing of 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. Based on computational predictions, we expect that monofunctional D. vulgaris CODH will have gas channels different from those of bifunctional Moorella thermoaceticacarbon monoxide dehydrogenase/acetyl‐CoA synthase (CODH/ACS). By pressurizing D. vulgaris CODH protein crystals with xenon and solving the structure to 2.04 Å resolution, we identify 12 xenon sites per CODH monomer, thereby elucidating hydrophobic channels used for CO transport. We find that D. vulgaris CODH has one CO channel that has not been experimentally validated previously in a CODH, and a second channel that is shared with Moorella thermoaceticacarbon 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.