Northwestern University and Stanford University researchers have engineered a fully synthetic metabolic system that converts a simple liquid molecule derived from carbon dioxide into a core building block of life, potentially opening a new route to convert captured CO2 into commercially valuable chemicals.
In the study, the team demonstrated that formate, a molecule produced from CO2 using electricity and water, can be converted into acetyl-CoA, a universal metabolite used by living cells to build and power essential biochemical processes. As a proof-of-concept, the researchers then used the same system to convert acetyl-CoA into malate, a valuable chemical used in products ranging from foods and cosmetics to biodegradable plastics.
The platform, dubbed the Reductive Formate Pathway (ReForm), differs from natural carbon-fixation pathways in a key way: it is entirely engineered and operates outside of living organisms. Built from redesigned enzymes, ReForm carries out a sequence of metabolic reactions that do not occur in nature, enabling chemical transformations that cells themselves struggle to perform.
The researchers framed the work as a response to the limits of biology in the face of rising atmospheric CO2. While nature has evolved multiple ways to process carbon dioxide, those pathways are not optimized for rapid, scalable conversion of industrially relevant inputs such as formate, and only a small set of microorganisms can naturally metabolize it efficiently—organisms that are often difficult to engineer for manufacturing.
To overcome those constraints, the team relied on cell-free synthetic biology, which uses the molecular “machinery” of cells—enzymes, cofactors and other components—without the cells themselves. By running the chemistry in a controlled test-tube environment, the researchers were able to precisely tune enzyme concentrations and reaction conditions, and rapidly evaluate large numbers of candidate enzymes.
Using the approach, they screened 66 enzymes and more than 3,000 enzyme variants to identify and optimize catalysts capable of performing the non-natural steps required for the pathway. The final design comprises six reaction steps, with five engineered enzymes converting one-carbon feedstocks into acetyl-CoA. The team also showed the system can accept multiple carbon inputs, including formate, formaldehyde, and methanol, expanding its potential usefulness as a modular carbon-upcycling platform.
The researchers said the next steps include further improving the pathway’s efficiency and using the same development toolkit to create additional enzymes and synthetic metabolic routes. The work was supported by the U.S. Department of Energy and the National Science Foundation and was published in Nature Chemical Engineering.
KEY QUOTES:
“The unabated release of CO2 has caused many pressing social and economic challenges for humanity. If we’re going to address this global challenge, we critically need new routes to carbon-negative manufacturing of goods. While nature has evolved several pathways to metabolize CO2, it is unable to keep up with the rapid increase in the amount of atmospheric CO2. Inspired by nature, we sought to use biological enzymes to convert formate derived from CO2 into more valuable materials. Because there isn’t a set of enzymes in nature that can do that, we decided to engineer one.”
“Cells naturally use metabolic reactions to convert one chemical into another. For example, cells can take glucose, or sugar, and convert it into energy. But, in nature, nothing can turn formate into acetyl-CoA. There are some enzymes that can act on formate, but they cannot build it up into something useful. So, we started with a theoretical pathway design and the need for enzymes with functionalities that did not exist in nature.”
“From here, we can imagine this work going in a couple different directions. We would like to further optimize this pathway and explore other designs to make one-carbon conversions more efficient. We also can imagine using the tools that we developed to engineer all kinds of other new enzymes and pathways. It gives us hope for a future where we can combine multiple technologies, both biological and abiological, in unique ways to find new solutions.”
Northwestern’s Ashty Karim, who co-led the study
“ReForm can readily use diverse carbon sources, including formate, formaldehyde and methanol. This is the first demonstration of a synthetic metabolic pathway architecture that can do so. By combining electrochemistry and synthetic biology, the ReForm pathway also expands possible solutions for generalizable CO2-fixation strategies. We anticipate that hybrid technologies that integrate the best of chemistry and the best of biology will provide transformative new directions for a carbon- and energy-efficient future.”
Stanford’s Michael Jewett, who co-led the study with Karim
