Gas channel rerouting in a primordial enzyme: Structural insights of the carbon-monoxide dehydrogenase/acetyl-CoA synthase complex from the acetogen Clostridium autoethanogenum

• Published in: Biochimica et biophysica acta. Bioenergetics 2021-01, Vol.1862 (1), p.148330, Article 148330
• Main Authors: Lemaire, Olivier N., Wagner, Tristan
• Format: Article
• Language: English
• Subjects: Acetogenesis; Acetyl Coenzyme A - chemistry; Acetyl Coenzyme A - metabolism; Aldehyde Oxidoreductases - chemistry; Aldehyde Oxidoreductases - metabolism; Bacterial Proteins - chemistry; Bacterial Proteins - metabolism; C1-metabolism; Carbon Monoxide - chemistry; Carbon Monoxide - metabolism; Clostridium - enzymology; CO-dehydrogenase/acetyl-CoA synthase; Crystallography, X-Ray; Gas channeling; Moorella - enzymology; Multienzyme Complexes - chemistry; Multienzyme Complexes - metabolism; Oxidation-Reduction; Protein Structure, Quaternary; Waste-gas conversion; X-ray crystal structure
• ISSN: 0005-2728; 1879-2650
• DOI: 10.1016/j.bbabio.2020.148330

Clostridium autoethanogenum, the bacterial model for biological conversion of waste gases into biofuels, grows under extreme carbon-monoxide (CO) concentrations. The strictly anaerobic bacterium derives its entire cellular energy and carbon from this poisonous gas, therefore requiring efficient molecular machineries for CO-conversion. Here, we structurally and biochemically characterized the key enzyme of the CO-converting metabolism: the CO-dehydrogenase/Acetyl-CoA synthase (CODH/ACS). We obtained crystal structures of natively isolated complexes from fructose-grown and CO-grown C. autoethanogenum cultures. Both contain the same isoforms and if the overall structure adopts the classic α2β2 architecture, comparable to the model enzyme from Moorella thermoacetica, the ACS binds a different position on the CODH core. The structural characterization of a proteolyzed complex and the conservation of the binding interface in close homologs rejected the possibility of a crystallization artefact. Therefore, the internal CO-channeling system, critical to transfer CO generated at the C-cluster to the ACS active site, drastically differs in the complex from C. autoethanogenum. The 1.9-Å structure of the CODH alone provides an accurate picture of the new CO-routes, leading to the ACS core and reaching the surface. Increased gas accessibility would allow the simultaneous CO-oxidation and acetyl-CoA production. Biochemical experiments showed higher flexibility of the ACS subunit from C. autoethanogenum compared to M. thermoacetica, albeit monitoring similar CO-oxidation and formation rates. These results show a reshuffling of internal CO-tunnels during evolution of these Firmicutes, putatively leading to a bidirectional complex that ensure a high flux of CO-conversion toward energy conservation, acting as the main cellular powerplant. [Display omitted] •Structure of the CODH/ACS complex solved from a waste gas-converting bacterium.•The CODH-ACS interface drastically differs from the model of Moorella thermoacetica.•The CODH dimer structure reveals the organization of C-clusters and CO-channels.•Internal CO tunneling system is reshuffled to fit the novel binding mode.•A porous gas channeling would allow bi-directionality during CO-autotrophic growth.