Elucidation of the Tailoring Steps in Julichrome Biosynthesis by Marine Gastropod Mollusk-Associated Streptomyces sampsonii SCSIO 054

The biosynthetic gene cluster governing the production of antibacterial julichromes was identified from marine gastropod mollusk-associated Streptomyces sampsonii SCSIO 054. Post-PKS assembly/tailoring enzymes JuiL, JuiM, JuiI, and JuiN represent key assembly enzymes. JuiL serves as a ketoreductase. JuiM is an acetyltransferase. JuiI carries out an intriguing biaryl coupling of two julichrome Q₆ units (immediate JuiL, JuiM product) to afford julichrome Q_6-6. JuiN carries out tailoring steps on julichrome Q_6-6, transforming Q_6-6 into Q_3-3.