Discovery and Biosynthesis of Persiathiacins: Unusual Polyglycosylated Thiopeptides Active against Multi-drug resistant Tuberculosis
Thiopeptides are ribosomally biosynthesized and post-translationally modified peptides (RiPPs) that potently inhibit the growth of Gram-positive bacteria by targeting multiple steps in protein biosynthesis. The poor pharmacological properties of thiopeptides, in particular their low aqueous solubility, has hindered their development into clinically useful antibiotics. Antimicrobial activity screens of a library of Actinobacterial extracts led to discovery of the novel polyglycosylated thiopeptides persiathiacins A and B from Actinokineospora sp. UTMC 2475 and Actinokineospora sp. UTMC 2448. Persiathiacin A is active against methicillin-resistant Staphylococcus aureus (MRSA) and several Mycobacterium tuberculosis strains, including drug-resistant and multidrug-resistant clinical isolates, and does not significantly affect the growth of ovarian cancer cells at concentrations up to 400 M. In vitro translation assays showed that, like other thiopeptide antibiotics, persiathiacin A targets protein biosynthesis. Polyglycosylated thiopeptides are extremely rare and nothing is known about their biosynthesis. Sequencing and analysis of the Actinokineospora sp. UTMC 2448 genome enabled identification of the putative persiathiacin biosynthetic gene cluster. A cytochrome P450 encoded by this gene cluster catalyses the hydroxylation of nosiheptide in vitro and in vivo, consistent with the proposal that the cluster directs persiathiacin biosynthesis. Several genes in the cluster encode homologues of enzymes known to catalyse the assembly and attachment of deoxysugars during the biosynthesis of other classes of glycosylated natural products. The discovery of the persiathiacins and their biosynthetic gene cluster thus provides the basis for the development of biosynthetic engineering approaches to the creation of novel (poly)glycosylated thiopeptide derivatives with enhanced pharmacological properties.