Unveiling the Post-PKS Redox Tailoring Steps in Biosynthesis of the Type II Polyketide Antitumor Antibiotic Xantholipin

SummaryXantholipin from Streptomyces flavogriseus is a curved hexacyclic aromatic polyketide antitumor antibiotic. The entire 52 kb xantholipin (xan) biosynthetic gene cluster was sequenced, and bioinformatic analysis revealed open reading frames encoding type II polyketide synthases, regulators, and polyketide tailoring enzymes. Individual in-frame mutagenesis of five tailoring enzymes lead to the production of nine xantholipin analogs, revealing that the xanthone scaffold formation was catalyzed by the FAD binding monooxygenase XanO4, the δ-lactam formation by the asparagine synthetase homolog XanA, the methylenedioxy bridge generation by the P450 monooxygenase XanO2 and the hydroxylation of the carbon backbone by the FAD binding monooxygenase XanO5. These findings may also apply to other polycyclic xanthone antibiotics, and they form the basis for genetic engineering of the xantholipin and similar biosynthetic gene clusters for the generation of compounds with improved antitumor activities.

Graphical AbstractFigure optionsDownload full-size imageDownload high-quality image (121 K)Download as PowerPoint slideHighlights► Cloning and sequencing of the complete xantholipin biosynthesis gene cluster ► Identification of genes for xanthone and methylenedioxy bridge formation ► An unusual C11 ketoreductase for the prearomatic reduction ► Multiple redox tailoring for type II PKS biosynthesis