Understanding forking enzymes could lead to more efficient production of renewable fuels and chemicals News

With support from the DOE’s Basic Energy Sciences Program, NREL researchers are unlocking the secrets of flavin-based electron bifurcation at the atomic level

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Enzymes are life: without these biological catalysts, the metabolic reactions that fuel the growth of bacteria, plants and animals would not occur at the speed necessary to sustain life.

Organisms control and manipulate energy in many ways to ensure cellular metabolism and survival. One method that the award-winning National Renewable Energy Laboratory (NREL) research team is focusing on is flavin-based electron bifurcation (FBEB).

A full understanding of the complex biochemistry of FBEBs can help design enzymatic processes so that energy from biomass or waste resources can be used more efficiently to produce biofuels or common chemicals at lower environmental and economic costs.

Funding from the U.S. Department of Energy’s Office of Science, Basic Energy Sciences (DOE-BES) program supported FBEB research at NREL through the Biological Electron Transfer and Catalysis Center (BETCy), a DOE-BES-funded Energy Frontier Research Center; DOE-BES Funded Core Program for Photosynthetic Energy Transduction; and a DOE-BES Early Career Award to Cara Lubner.

“The NREL team’s work on bifurcation provides a critical scientific basis for improving processes for more efficient renewable fuels and chemicals,” said Bill Tumas, deputy laboratory director in the Materials, Chemistry and Computation Directorate and NREL’s BES point of contact.

Unraveling the mechanistic secrets of flavin-based electron bifurcation

FBEB has recently gained acceptance as a primary mechanism for producing and conserving biological energy. What was unknown was how this mechanism worked.

So a team from NREL and partner universities across the country began investigating the secrets of the FBEB mechanism. Cara Lubner, David Mulder, and Paul King led the NREL team and investigated previously unknown features of flavin-based enzymes to understand how they generate two levels of energy during the FBEB reaction.

They discovered key design features of FBEB enzymes that allow the energy level of an electron pair to be bifurcated into low and high energy levels, which are distributed between chemical reactions with different energy demands.

“The team’s discoveries uncovered how electrons move around the heart of the enzyme, leading to an understanding of how the enzyme solves the problem of conducting an energy-intensive chemical reaction at room temperature and pressure,” said Maureen McCann, director of the Center for Biological Sciences at NREL. “In the long term, knowledge of the fundamental mechanisms at the atomic and electronic levels opens up transformation possibilities that enable energy-intensive chemical reactions to be carried out on an industrial scale.”

NREL’s unique technical capabilities enable insight into FBEB enzymes at the atomic level

To decipher the inner workings of the FBEB enzymes, the team leveraged NREL’s unique technical capabilities, including the Advanced Spin Resonance Facility and the Ultrafast Optical Biophysics Laboratory for electron paramagnetic resonance (EPR) and transient absorption spectroscopy methods.

Together, this made it possible to study at the atomic level how the enzyme’s electronic circuitry, which includes a flavin cofactor and iron-sulfur clusters, enables the sharing of electron pairs in reactions between substrates and products.

The results revealed key thermodynamic and electron spin properties of the circuits that are ultimately responsible for controlling electron flow in the enzyme, leading to the formation of FBEB. Because FBEB is a departure from what normally occurs during a metabolic reaction, i.e. losing energy as heat and producing lower energy products, the effect is energy saving.

The team published the study “Mechanistic insights into energy conservation by flavin-based electron bifurcation” in: Nature Chemical Biology.

NREL scientists receive the 2023 Faraday Horizon Award for electron bifurcation research

This groundbreaking work on electron bifurcation also resulted in additional accolades. Cara Lubner, David Mulder and Paul King of NREL and a number of university partners have received the 2023 Faraday Horizon Prize from the British Royal Society of Chemistry.

The Faraday Horizon Prizes are awarded to recognize recent significant new discoveries or advances in physical chemistry. The prize was awarded for “the successful discovery of the principles underlying how living systems divide electron pairs into high- and low-energy pools without causing energy-wasting ‘short-circuit’ reactions.”

Congratulations to the NREL team and university partners on this award.

Learn more about basic energy science at NREL or the U.S. Department of Energy’s Office of Science.