Unsymmetrically Regioselective Homodimerization Depends on theSubcellular Colocalization of Laccase/Fasciclin Protein in theBiosynthesis of Phlegmacins

Phlegmacins are homodimeric dihydroanthracenonenatural products featuring two torosachrysone monomers unsymmetri-cally conjugated by 7,10 '-coupling. Herein, we report the identificationand characterization of the biosynthetic gene cluster of phlegmacins inascomyceteTalaromycessp. F08Z-0631. On the basis of theheterologous reconstitution of the phlegmacin pathway inAspergillusoryzae, we demonstrated an unprecedented laccase-involved unsym-metrically regioselective oxidative coupling reaction. The association oflaccase PhlC and the fasciclin partner protein PhlB was verified to beindispensable for the coupling activity. Intriguingly, both proteins can betransferred and located independently at the mitochondrial membrane.Notably, only their subcellular colocalization led to the occurrence ofoxidative dimerization. These observations add new insights into thepoorly understood catalytic mechanisms of various laccases involved inthe biosynthesis of secondary metabolites, particularly those functioning with variable partners

Automated summary

This study identified and characterized the biosynthetic gene cluster of phlegmacins in ascomycete Talaromyces sp. F08Z-0631, and demonstrated an unprecedented enzymatic coupling reaction through heterologous reconstitution. These findings provide new insights into the catalytic mechanisms of enzymes involved in the biosynthesis of secondary metabolites.