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.

As the scientific community seeks sustainable solutions to reduce our carbon dioxide (CO₂) footprint, nature offers inspiration: in addition to photosynthetic carbon fixation, there are other natural CO­­₂ fixation pathways used by different organisms. Understanding how these pathways work at an atomic level is an important goal on the road to engineering climate solutions. The oldest known CO­₂-fixation pathway, used in many oxygen-free environments, is known as the Wood-Ljungdahl pathway. This pathway is highly energy-efficient, allowing some anaerobic bacteria and archaea to grow using the energy they generate through CO₂ fixation.

Now, a multidisciplinary team from the Max Planck Institutes of Biophysics, Marine Microbiology and, Molecular Cell Biology and Genetics, led by Bonnie Murphy, Gerhard Hummer and Tristan Wagner, worked together to solve the mysteries of the central enzyme of the Wood-Ljungdahl pathway, known as 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 this 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 gas-based bioreactors. Their findings provide a far more complete picture of the CODH/ACS mechanism. The authors highlight that the acetyl-CoA synthase does a complicated molecular choreography, rearranging and interacting with partner molecules in the cell, to be able to make acetyl-CoA.

According to Max Yin, a postdoc at the Max Planck Institute of Biophysics and one of the lead authors on the study, although this protein complex has been studied in the past, there was a lot still unknown about how it works at an atomic level. Altogether, the resolved atomic structures allowed the authors to draw a detailed reaction mechanism of the CODH/ACS enzyme, crucial for CO₂ fixation in anaerobic organisms.