Hydroxyl regioisomerization of anthracycline catalyzed by a four-enzyme cascade

Significance Enzymatic modifications of anthracycline antibiotics are urgently needed in the fields of biosynthesis, biocatalysis, and even medical chemistry. However, neither hydroxyl regioisomerization nor dehydroxylation of anthracycline core was described previously. Here, we discover an unprecedented hydroxyl regioisomerization process in the biosynthesis of a rare carbon-4 deoxyanthracycline, which includes three tailoring steps performed by a four-enzyme cascade: two-component hydroxylases mediated a cryptic hydroxylation, and two NmrA-like short-chain dehydrogenase/reductases catalyzed a reduction-dearomatization followed by a reduction-dehydration process. This study expands the enzymology and chemistry of type II polyketide synthase and provides tools to generate more analogs by engineering or enzymatic semisynthesis.