A new thermophilic ene‐reductase from the filamentous anoxygenic phototrophic bacterium Chloroflexus aggregans

Aiming at expanding the biocatalytic toolbox of ene‐reductase enzymes, we decided to explore photosynthetic extremophile microorganisms as unique reservoir of (new) biocatalytic ac-tivities. We selected a new thermophilic ene‐reductase homologue in Chloroflexus aggregans, a pe-culiar filamentous bacterium. We report here on the functional and structural characterization of this new enzyme, which we called CaOYE. Produced in high yields in recombinant form, it proved to be a robust biocatalyst showing high thermostability, good solvent tolerance and a wide range of pH optimum. In a preliminary screening, CaOYE displayed a restricted substrate spectrum (with generally lower activities compared to other ene‐reductases); however, given the amazing metabolic ductility and versatility of Chloroflexus aggregans, further investigations could pinpoint pecu-liar chemical activities. X‐ray crystal structure has been determined, revealing conserved features of Class III (or thermophilic‐like group) of the family of Old Yellow Enzymes: in the crystal pack-ing, the enzyme was found to assemble as dimer even if it behaves as a monomer in solution. The description of CaOYE catalytic properties and crystal structure provides new details useful for en-larging knowledge, development and application of this class of enzymes.