Structure and biosynthetic implication of 5R-(N-acetyl-L-cysteinyl)-14S-hydroxy-dihydrokalafungin from a mutant of the actVA-ORF4 gene for actinorhodin biosynthesis in Streptomyces coelicolor A3(2).

Actinorhodin (ACT, 1), an aromatic polyketide produced by Streptomyces coelicolor A3(2),1 belongs to a class of benzoisochromanequinone (BIQ) antibiotics (Figure 1a).2 Because 1 has a symmetrical structure in which two BIQ units are coupled via a C–C bond, its enzymatic formation in a regiospecific manner has drawn considerable attention. ACT biosynthesis is controlled by the act cluster, which comprises 22 genes, and the functions of several genes remain elusive.