The leader peptide is essential for the post‐translational modification of the DNA‐gyrase inhibitor microcin B17

ABSTRACT Microcin B17 (MccB17) is a peptide antibiotic produced by Escherichia coli strains carrying the pMccB17 plasmid. MccB17 is synthesized as a precursor containing an amino-terminal leader peptide that is cleaved during maturation. Maturation requires the product of the chromosomal tldE (pmbA) gene. Mature microcin is exported across the cytoplasmic membrane by a dedicated ABC transporter. In sensitive cells, MccB17 targets the essential topoisomerase II DNA gyrase. Independently, tldE as well as tldD mutants were isolated as being resistant to CcdB, another natural poison of gyrase encoded by the ccd poison-antidote system of plasmid F. This led to the idea that TldD and TldE could regulate gyrase function. We present in vivo evidence supporting the hypothesis that TldD and TldE have proteolytic activity. We show that in bacterial mutants devoid of either TldD or TldE activity, the MccB17 precursor accumulates and is not exported. Similarly, in the ccd system, we found that TldD and TldE are involved in CcdA and CcdA41 antidote degradation rather than being involved in the CcdB resistance mechanism. Interestingly, sequence database comparisons revealed that these two proteins have homologues in eubacteria and archaebacteria, suggesting a broader physiological role.

Download Full-text

Posttranslational modifications in microcin B17 define an additional class of DNA gyrase inhibitor.

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.91.10.4519 ◽

1994 ◽

Vol 91 (10) ◽

pp. 4519-4523 ◽

Cited By ~ 108

Author(s):

P. Yorgey ◽

J. Lee ◽

J. Kordel ◽

E. Vivas ◽

P. Warner ◽

...

Keyword(s):

Posttranslational Modifications ◽

Dna Gyrase ◽

Microcin B17

Download Full-text

Protective Effect of Qnr on Agents Other than Quinolones That Target DNA Gyrase

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.01292-15 ◽

2015 ◽

Vol 59 (11) ◽

pp. 6689-6695 ◽

Cited By ~ 16

Author(s):

George A. Jacoby ◽

Marian A. Corcoran ◽

David C. Hooper

Keyword(s):

Protective Effect ◽

Dna Gyrase ◽

Molecular Probes ◽

Protective Activity ◽

Topoisomerase Iv ◽

Synthetic Compounds ◽

Target Dna ◽

Simocyclinone D8 ◽

Microcin B17 ◽

Insight Into

ABSTRACTQnr is a plasmid-encoded and chromosomally determined protein that protects DNA gyrase and topoisomerase IV from inhibition by quinolones. Despite its prevalence worldwide and existence prior to the discovery of quinolones, its native function is not known. Other synthetic compounds and natural products also target bacterial topoisomerases. A number were studied as molecular probes to gain insight into how Qnr acts. Qnr blocked inhibition by synthetic compounds with somewhat quinolone-like structure that target the GyrA subunit, such as the 2-pyridone ABT-719, the quinazoline-2,4-dione PD 0305970, and the spiropyrimidinetrione pyrazinyl-alkynyl-tetrahydroquinoline (PAT), indicating that Qnr is not strictly quinolone specific, but Qnr did not protect against GyrA-targeting simocyclinone D8 despite evidence that both simocyclinone D8 and Qnr affect DNA binding to gyrase. Qnr did not affect the activity of tricyclic pyrimidoindole or pyrazolopyridones, synthetic inhibitors of the GyrB subunit, or nonsynthetic GyrB inhibitors, such as coumermycin A1, novobiocin, gyramide A, or microcin B17.Thus, in this set of compounds the protective activity of Qnr was confined to those that, like quinolones, trap gyrase on DNA in cleaved complexes.

Download Full-text

Prevalence of Plasmid-Mediated Quinolone Resistance

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.47.2.559-562.2003 ◽

2003 ◽

Vol 47 (2) ◽

pp. 559-562 ◽

Cited By ~ 150

Author(s):

George A. Jacoby ◽

Nancy Chow ◽

Ken B. Waites

Keyword(s):

Medical Center ◽

Dna Gyrase ◽

The United States ◽

Quinolone Resistance ◽

Clinical Strain ◽

University Of Alabama ◽

Repeat Family ◽

Gyrase A ◽

The University ◽

Microcin B17

ABSTRACT Quinolone resistance encoded by the qnr gene and mediated by plasmid pMG252 was discovered in a clinical strain of Klebsiella pneumoniae that was isolated in 1994 at the University of Alabama at Birmingham Medical Center. The gene codes for a protein that protects DNA gyrase from quinolone inhibition and that belongs to the pentapeptide repeat family of proteins. The prevalence of the gene has been investigated by using PCR with qnr-specific primers with a sample of more than 350 gram-negative strains that originated in 18 countries and 24 states in the United States and that included many strains with plasmid-mediated AmpC or extended spectrum β-lactamase enzymes. qnr was found in isolates from the University of Alabama at Birmingham only during 6 months in 1994, despite the persistence of the gene for FOX-5 β-lactamase, which is linked to qnr on pMG252. Isolates from other locations were negative for qnr. The prevalence of mcbG in the same sample was also examined. mcbG encodes another member of the pentapeptide repeat family and is involved in immunity to microcin B17, which, like quinolones, targets DNA gyrase. A single clinical isolate contained mcbG on a transmissible R plasmid. This plasmid and one carrying the complete microcin B17 operon slightly decreased sparfloxacin susceptibility but had a much less protective effect than pMG252. Plasmid-mediated quinolone resistance was thus rare in the sample examined.

Download Full-text