Structure and Biosynthesis of Aridomycins Reveal a Glycosylated Prodrug Strategy for Self-Resistance

Polyketides, nonribosomal peptides, and their hybrids constitute a major class of clinically important antibiotics. To avoid self-toxicity, producing organisms must employ mechanisms of self-resistance. Here, we describe the structures, biosynthesis, and self-resistance strategy of the aridomycins, new linear polyketide antibiotics. Using NMR spectroscopy, whole genome sequencing, and bioinformatics, we determined the absolute configurations of all 28 stereocenters and identified a previously unrecognized acyltransferase specificity motif (GHSQ···FVAH) associated with hydroxymalonyl-ACP incorporation. We also assigned the biosynthetic gene cluster (BGC) for aridomycin, as well as for blasticidin A, a polyketide structurally related to the well-characterized aflastatin A, both of which support the new AT motif assignment. Interestingly, aridomycin A, the glycosylated congener, lacked antimicrobial activity against multidrug-resistant pathogens and the producing Amycolatopsis strains. Its temporal production preceding the aglycone aridomycin B, together with substrate specificity studies of the glycosyltransferase AriGT, indicate that reversible glucosylation acts as a self-resistance mechanism. To our knowledge, this represents the first example of such a strategy outside the macrolide class.