Discovery and Biosynthesis of Gladiolin: A Burkholderia gladioli Antibiotic with Promising Activity against Mycobacterium tuberculosis

Stewart Cole, Ruben Hartkoorn, Anthony Vocat
Amer Chemical Soc, 2017
Article

Résumé

An antimicrobial activity screen of Burkholderia gladioli BCC0238, a clinical isolate from a cystic fibrosis patient, led to the discovery of gladiolin, a novel macrolide antibiotic with potent activity against Mycobacterium tuberculosis H37Rv. Gladiolin is structurally related to etnangien, a highly unstable antibiotic from Sorangium cellulosum that is also active against Mycobacteria. Like etnangien, gladiolin was found to inhibit RNA polymerase, a validated drug target in M. tuberculosis. However, gladiolin lacks the highly labile hexaene moiety of etnangien and was thus found to possess significantly increased chemical stability. Moreover, gladiolin displayed low mammalian cytotoxicity and good activity against several M. tuberculosis clinical isolates, including four that are resistant to isoniazid and one that is resistant to both isoniazid and rifampicin. Overall, these data suggest that gladiolin may represent a useful starting point for the development of novel drugs to tackle multidrug-resistant tuberculosis. The B. gladioli BCC0238 genome was sequenced using Single Molecule Real Time (SMRT) technology. This resulted in four contiguous sequences: two large circular chromosomes and two smaller putative plasmids. Analysis of the chromosome sequences identified 49 putative specialized metabolite biosynthetic gene clusters. One such gene cluster, located on the smaller of the two chromosomes, encodes a trans-acyltransferase (trans-AT) polyketide synthase (PKS) multienzyme that was hypothesized to assemble gladiolin. Insertional inactivation of a gene in this cluster encoding one of the PKS subunits abrogated gladiolin production, confirming that the gene cluster is responsible for biosynthesis of the antibiotic. Comparison of the PKSs responsible for the assembly of gladiolin and etnangien showed that they possess a remarkably similar architecture, obfuscating the biosynthetic mechanisms responsible for most of the structural differences between the two metabolites.

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Stewart Cole, Ruben Hartkoorn, Anthony Vocat
Amer Chemical Soc, 2017
Article

Résumé

Official source

https://infoscience.epfl.ch/record/229591?ln=fr

À propos de ce résultat

Concepts associés (17)

Concepts associés

Chargement

Publications associées (114)

Publications associées

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Multidrug-resistant tuberculosis (MDR-TB) poses a serious threat to global public health. The mutations responsible for drug resistance in Mycobacterium tuberculosis have been identified, but what impact these mutations have on bacterial fitness is controversial. We analyzed 3 MDR strains of M. tuberculosis obtained from human immunodeficiency virus-negative patients with chronic pulmonary TB. One of these strains harbored a chromosomal deletion encompassing 15 open reading frames. Genes deleted in this strain included acr1, which encodes the virulence factor alpha-crystallin (Acr) 1, a protein that has been reported to be essential for M. tuberculosis replication in macrophages. We found that all 3 MDR isolates, including the acr1-deficient strain, replicated in cultured murine and human macrophages with the same kinetics as H37Rv, a virulent laboratory strain. These observations challenge the prevailing view that MDR bacteria are less fit than drug-susceptible bacteria and indicate that Acr1 is dispensable for bacterial growth in the human lung.

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The tolerance of Mycobacterium tuberculosis to anti-tuberculosis drugs is a major reason for the lengthy therapy needed to treat a tuberculosis infection. Rifampin is a potent inhibitor of RNA polymerase (RNAP) in vivo, but has been shown to be less effective against stationary phase bacteria. Sigma factor F is associated with bacteria entering stationary phase and has been proposed to impact rifampin activity. Here we investigate whether RNAP containing SigF is more resistant to rifampin inhibition in vitro, and whether over-expression of sigF renders M. tuberculosis more tolerant to rifampin. Real-time and radiometric in vitro transcription assays revealed that rifampin equally inhibits transcription by RNAP containing sigma factors SigA and SigF, therefore ruling out the hypothesis that SigF may be responsible for increased resistance of the enzyme to rifampin in vitro. In addition, over-expression or deletion of sigF did not alter rifampin susceptibility in axenic cultures of M. tuberculosis, indicating that SigF does not affect rifampin tolerance in vivo.

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Characterization of the katG gene encoding a catalase-peroxidase required for the isoniazid susceptibility of Mycobacterium tuberculosis.

Stewart Cole, Ye Zhang

The isoniazid susceptibility of Mycobacterium tuberculosis is mediated by the product of the katG gene which encodes the heme-containing enzyme catalase-peroxidase. In this study, the chromosomal location of katG has been established and its nucleotide sequence has been determined so that the primary structure of catalase-peroxidase could be predicted. The M. tuberculosis enzyme is an 80,000-dalton protein containing several motifs characteristic of peroxidases and shows strong similarity to other bacterial catalase-peroxidases. Expression of the katG gene in M. tuberculosis, M. smegmatis, and Escherichia coli was demonstrated by Western blotting (immunoblotting). Homologous genes were detected in other mycobacteria, even those which are naturally insensitive to isoniazid.

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