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Green chemistry and biofuel: the functioning of a key photoenzyme deciphered


​An international consortium of scientists, including an I2BC team, has just deciphered the functioning of FAP (Fatty Acid Photodecarboxylase), a key photoenzyme for the production of biofuels and other high value added molecules. This work, published in Science, was the object of a CEA press release

Published on 12 April 2021
​ This study involved researchers from the Institut de Biosciences et Biotechnologies d'Aix-Marseille in Cadarache, the Institut de Biologie Intégrative de la Cellule in Gif-sur-Yvette, the Institut Polytechnique de Paris in Palaiseau, the Institut de Biologie Structurale in Grenoble, the Universities of Lille and Rennes, the European Synchrotron Radiation Facility and the Institute Laue Langevin (both in Grenoble), the Max-Planck Institute in Heidelberg, the Moscow State University and the SLAC National Accelerator Laboratory in USA.

Photoenzymes are very rare biocatalysts that use light to perform their chemical reaction. Among the handful of natural photoenzymes identified so far, the Fatty Acid Photodecarboxylase (FAP) recently discovered in a microalga (Chlorella) is involved in the generation of hydrocarbons from fatty acids, a process that bears great promise for the production of biofuels and the generation of high-value chemicals. However, how the enzyme accomplishes its function at the molecular level has remained elusive. The observation of the functioning of FAP at the molecular level has just been achieved by an international consortium of scientists (see box). A key to success was the unprecedented combination of multi-faceted experimental and theoretical approaches comprising site-directed mutagenesis, cryotrapping of reaction intermediates, static and kinetic crystallography at synchrotrons and an X-ray free electron laser (XFEL), Fourier-transform infrared spectroscopy (FTIR), time-resolved vibrational and electronic optical spectroscopies and quantum chemical calculations.

Electron transfer (in 300 picoseconds) from the fatty acid substrate to a photo-excited flavin (a yellow enzyme-incorporated vitamin B2-derivative) initiates catalysis in FAP. The consortium established that this event quasi-instantaneously leads to the fundamental catalytic step: dissociation of the substrate into hydrocarbon precursor and carbon dioxide (CO2). A big surprise is the discovery that the majority of the generated CO2 is quickly (100 nanoseconds) transformed into bicarbonate (HCO3) within the enzyme, involving a water molecule and a particular amino acid. Another unexpected finding is an unusual bent conformation of the flavin molecule, which shifts its absorption to the red, so that it harvests photons not exploited by the photosynthetic activity of the microalga. The combined interpretation of results from the diverse and complementary experimental and computational approaches now provides a detailed, atomic-scale picture of FAP at work (Figure).



Artist impression of the enzymatic catalysis proposed in mechanism and dynamics of fatty-acid photodecarboxylase (Science, 2021) © D Sorigué/CEA


The FAP photoenzyme constitutes a novel opportunity for sustainable production of non-fossil hydrocarbon biofuels: by using light, fatty acids produced by microorganisms can be transformed by FAP, in a single step, to hydrocarbons that would be readily usable as fuel. FAP also holds great promises for the light-driven decarboxylation of functionalized carboxylic acids to form high-value chemicals. The elucidation of FAP catalytic mechanism constitutes a solid basis for the optimization of the enzyme for the production of 'green' hydrocarbon fuels and chemicals.

Contacts: for BIAM: Frédéric Beisson (frederic.beisson@cea.fr); for I2BC: Pavel Müller (pavel.muller@i2bc.paris-saclay.fr); for LOB: Marten Vos (marten.vos@polytechnique.edu); for IBS: Martin Weik (weik@ibs.fr ).

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