Pradimicin B

Pradimicins are potent antifungal antibiotics with effective inhibitory effects against HIV-1. Pradimicin A consists of an unusual dihydrobenzo[α]naphthacenequinone aglycone substituted with a combination of D-alanine and two sugar moieties. Detailed genetic studies revealed most steps in pradimicin A biosynthesis, but the glycosylation mechanism remained inconclusive. The biosynthetic gene cluster of pradimicin A contains two putative glycosyltransferases, pdmQ and pdmS. However, the exact involvement of each gene in biosynthesis and the particular steps required for precise structural modification was unknown. In this study, the exact role of each gene was evaluated by insertional inactivation and complementation studies. Analysis of the metabolite from both of the disruption mutants revealed abolishment of pradimicin A and complementation resulted in the recovery of production. After deletion of pdmQ, pradimicin B was found to accumulate, whereas deletion of pdmS resulted in the accumulation of aglycone of pradimicin. Together, these results suggest that pdmS is responsible for the attachment of thomosamine to form pradimicin B which in turn is glycosylated by pdmQ to form pradimicin A. These results allowed us to deduce the exact order of terminal tailoring by glycosylation and provided insight into the mechanism of pradimicin A biosynthesis.

The biosynthetic pathway of pradimicin S (PRM-S) was investigated by using sinefungin and bioconversion experiments with aglycones of pradimicin A (PRM-A) and Actinomadura spinosa AA0851, a PRM-S producer. Addition of sinefungin to the strain inhibited the formation of 11-O-demethyl-7-O-methylpradinone II (11dM-7M-PNII) as also determined to occur with its addition to the PRM-A producer. In feeding PRM-A aglycone and its analogs to the strain early in PRM-S biosynthesis, good identifications of bioconverted products were obtained by frit-FAB LC/MS as follows: 11-O-demethylpradinone II (11dM-PNII), 11dM-7M-PNII, 11-O-demethylpradinone I (11dM-PNI), 11-O-demethylpradimicinone I (11dM-PMNI) and pradimicinone I (PMNI) were converted to PRM-S. Pradimicin B (PRM-B) and pradimicin L (PRM-L) were converted to PRMs-L and -S and PRM-S, respectively. A biosynthetic pathway for PRM-S is proposed.

Pradimicins are antifungal and antiviral natural products from Actinomadura hibisca P157-2. The sugar moieties play a critical role in the biological activities of these compounds. There are two glycosyltransferase genes in the pradimicin biosynthetic gene cluster, pdmS and pdmQ, which are putatively responsible for the introduction of the sugar moieties during pradimicin biosynthesis. In this study, we disrupted these two genes using a double crossover approach. Disruption of pdmS led to the production of pradimicinone I, the aglycon of pradimicin A, which confirmed that PdmS is the O-glycosyltransferase responsible for the first glycosylation step and attaching the 4',6'-dideoxy-4'-amino-d-galactose or 4',6'-dideoxy-4'-methylamino-d-galactose moiety to the 5-OH. Disruption of pdmQ resulted in the production of pradimicin B, indicating that this enzyme is the second glycosyltransferase that introduces the d-xylose moiety to the 3'-OH of the first sugar moiety. Insertion of an integrative plasmid before pdmO might have interfered with the dedicated promoter, yielding a mutant that produces pradimicin C as the major metabolite, which suggested that PdmO is the enzyme that specifically methylates the 4'-NH2 of the 4',6'-dideoxy-4'-amino-d-galactose moiety. Functional characterization of these sugar-decorating and -incorporating enzymes thus facilitates the understanding of the pradimicin biosynthetic pathway.