Control of Carbon-Carbon Bond Cleavage by Radical SAM Enzymes – CARBONARA

Natural products and their biosynthetic routes are important sources of inspiration for chemists in their search for new environment-friendly and still highly efficient routes for the synthesis of fine chemicals. Carbon-carbon bond formation and cleavage are among the most difficult reactions. They usually require preliminary activation steps through the insertion of several, often transitory, functional groups. This frequently leads to an increase in the number of steps and a concomitant drop in the yields. Radical-based chemistry is a good alternative, thanks to its unique ability to activate otherwise unreactive positions such as aliphatic carbon atoms. The downside of this approach is that radical-based reactions are really difficult to control. In Nature, radical S-adenosyl-L-methionine (rSAM) enzymes are versatile radical catalysts capable of performing and tightly controlling over seventy different chemical reactions.
With the CARBONARA project, we aim at determining the factors that control and drive radical-based C-C bond cleavage in rSAM enzymes. We want to address the key issues of substrate selectivity and activation, and the questions as to how these proteins control the radical-based chemistry to cleave one particular C-C bond over another and what tightly controls the termination of the reaction and the final products that are formed. To achieve these goals, we have selected five proteins with similar folds, readily available within the consortium, that catalyze C-C bond cleavage in amino acids.
Our consortium consists of three internationally renowned partners with complementary expertise in the fields of biochemistry, structural biology and spectroscopy covering the fundamentals of this fascinating chemistry. Using X-ray crystallography, in vitro functional analyses, electron paramagnetic resonance spectroscopy and theoretical calculations, we want to characterize the functional, structural and electronic parameters that control the C-C cleavage reaction. In this way, we expect to understand and identify the key factors, which are intrinsic to the radical-based reaction itself and the extrinsic ones controlled by the protein matrix. Our original multidisciplinary approach should not only favor a more rational use of radical-based chemistry in organic synthesis, but also lay the foundations for the use of rSAM enzymes as new tools in synthetic biology, in particular through the development of rationally designed chimeras.