Biosynthesis of clinically used antibiotic fusidic acid and identification of two short-chain dehydrogenase/reductases with converse stereoselectivity.

Fusidic acid is the only fusidane-type antibiotic that has been clinically used. However, biosynthesis of this important molecule in fungi is poorly understood. We have recently elucidated the biosynthesis of fusidane-type antibiotic helvolic acid, which provides us with clues to identify a possible gene cluster for fusidic acid ( cluster). This gene cluster consists of eight genes, among which six are conserved in the helvolic acid gene cluster except and . Introduction of the two genes into the NSAR1 expressing the conserved six genes led to the production of fusidic acid. A stepwise introduction of and revealed that the two genes worked independently without a strict reaction order. Notably, we identified two short-chain dehydrogenase/reductase genes and in the cluster, which showed converse stereoselectivity in 3-ketoreduction. This is the first report on the biosynthesis and heterologous expression of fusidic acid.