The FAD-Dependent Monooxygenase Albo65 Mediates Self-Resistance in Albofungin Biosynthesis.

The production of specialized small molecules in microorganisms often involves self-resistance mechanisms to prevent autotoxicity. Albofungins belong to the xanthone-containing aromatic polyketides with potent antimicrobial activities. However, its self-resistance mechanism remains unknown. Here we report the discovery of a flavin adenine dinucleotide (FAD)-dependent monooxygenase, Albo65, that mediates self-resistance in albofungin biosynthesis in Streptomyces monomycini NRRL B-24309. Deletion of albo65 resulted in almost no albofungin production and increased the sensitivity of the mutant strain to albofungin. Heterologous expression of albo65 in a nonproducing host increased the resistance of the host to albofungin. Biochemical studies showed that Albo65 catalyzes the oxidative inactivation of albofungin in vitro, and the resulting reaction mixture exhibited reduced antibacterial activity. Based on this discovery, the albofungin-albo65 pair was successfully developed as a highly sensitive selection system for yeasts. This work provides insights into the self-resistance mechanisms in albofungin biosynthesis and explores potential applications of Albo65 in basic and applied biological research.