Radical SAM enzymes (rSAM) and oxygenases are two of the most common and versatile metalloprotein structural domains in nature. In collaboration with groups from Singapore and China, we have identified a group of fused rSAM-oxygenase enzymes that catalyze crosslink formation and OH addition in ribosomally synthesized and translationally modified peptides (RiPPs). Crystal structure determination of the oxygenase domain, revealed a novel structural fold, named $\alpha$KG-HExxH, different to the well-known jelly-roll fold characteristic of α-ketoglutarate and non-haem iron oxygenases. The novel αKG-HExxH fold, which evolved from Zn proteases, extends the family of α-ketoglutarate non-haem iron enzymes and represents a unique family of ribosomally synthesized and post-translationally modified peptide modifying enzymes. The discovery of a fusion of αKG-HExxH oxygenase with an rSAM domain is fascinating because the necessity of molecular oxygen to catalyze hydroxylations in such close proximity to the rSAM domain, which contains FeS clusters sensitive to oxygen-induced inactivation, requires a highly dynamic regulation between the fused enzymatic domains. The observed natural fusion will undoubtedly lead to the synthesis of medically relevant natural products by such enzymes.
Fused radical SAM and αKG-HExxH domain proteins contain a distinct structural fold and catalyse cyclophane formation and β-hydroxylation. Morishita, Y., Ma, S., De La Mora, E. et al. Nat. Chem. 2024 ; doi : 10.1038/s41557-024-01596-9.
Contact : Yvain Nicolet, Metalloproteins Group (IBS/METALLO)