The Molecular Choreography of Efficient Microbial Carbon Capture

A new structural study reveals the mechanism used by anaerobic microbes to grow on waste gases
 

Researchers at three collaborating Max Planck Institutes have unveiled the process by which certain single-celled microorganisms convert carbon dioxide into energy-rich compounds in oxygen-free environments. An understanding of this mechanism has the potential to inspire and inform biological and biomimetic carbon-capture strategies.
 

Text: Pamela Ornelas

As the scientific community seeks sustainable solutions to reduce our carbon dioxide (CO₂) footprint, nature offers an abundance of inspiration. In addition to photosynthesis, six other natural pathways are known by which living organisms remove CO­­₂ from the atmosphere to turn it into biomass. Understanding how these pathways work at an atomic level is an important step on the road to engineering climate solutions. The oldest CO­₂-fixation pathway, used in many oxygen-free environments, is known as the Wood-Ljungdahl pathway (WLP). The WLP is the most energy-efficient CO₂-fixation pathway, allowing anaerobic bacteria and archaea to generate ATP through CO₂ fixation.

A multidisciplinary work, led by Bonnie Murphy, Gerhard Hummer and Tristan Wagner, and involving researchers from the Max Planck Institutes of Biophysics, Marine Microbiology and, Molecular Cell Biology and Genetics, solved the mysteries of the central enzyme of the WLP: the Carbon Monoxide Dehydrogenase/Acetyl-CoA Synthase (CODH/ACS) complex. This enzyme performs a dual function, first transforming CO₂ to carbon monoxide (CO), and then using the CO to produce a central building block of metabolism called acetyl-CoA.

Using a combination of electron microscopy, X-ray crystallography, and computational techniques, Yin and Lemaire et al. studied the architecture of CODH/ACS from the bacterium Clostridium autoethanogenum, a microbe that is used in industrial bioreactors to turn industrial waste gasses into biofuels. Their findings, published in the journal Science, provide a far more complete picture of how the complex carries out the demanding reactions of CO₂ fixation. Max Yin, a postdoc at the MPI of Biophysics and one of the lead authors on the study, commented on the findings: ‘Although this protein complex has been studied in the past, there was still a lot still unknown about how it works at an atomic level. In particular, the acetyl-CoA synthase does a complicated molecular dance, rearranging and interacting with partner molecules in the cell, to be able to make acetyl-CoA’.