Biochemical and structural characterization of mycobacterial aspartyl-tRNA synthetase AspS, a promising TB drug target

Sudagar S. Gurcha, Veeraraghavan Usha, Jonathan A.G. Cox, Klaus Fütterer, Katherine A. Abrahams, Apoorva Bhatt, Luke J. Alderwick, Robert C. Reynolds, Nicholas J. Loman, Vijayashankar Nataraj, Carlos Alemparte, David Barros, Adrian J. Lloyd, Lluis Ballell, Judith V. Hobrath, Gurdyal S. Besra

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23 Citations (Scopus)

Abstract

The human pathogen Mycobacterium tuberculosis is the causative agent of pulmonary tuberculosis (TB), a disease with high worldwide mortality rates. Current treatment programs are under significant threat from multi-drug and extensively-drug resistant strains of M tuberculosis, and it is essential to identify new inhibitors and their targets. We generated spontaneous resistant mutants in Mycobacterium bovis BCG in the presence of 10× the minimum inhibitory concentration (MIC) of compound 1, a previously identified potent inhibitor of mycobacterial growth in culture. Whole genome sequencing of two resistant mutants revealed in one case a single nucleotide polymorphism in the gene aspS at 535GAC535AAC (D179N), while in the second mutant a single nucleotide polymorphism was identified upstream of the aspS promoter region. We probed whole cell target engagement by overexpressing either M. bovis BCG aspS or Mycobacterium smegmatis aspS, which resulted in a ten-fold and greater than ten-fold increase, respectively, of the MIC against compound 1. To analyse the impact of inhibitor 1 on M. tuberculosis AspS (Mt-AspS) activity we over-expressed, purified and characterised the kinetics of this enzyme using a robust tRNA-independent assay adapted to a high-throughput screening format. Finally, to aid hit-to-lead optimization, the crystal structure of apo M. smegmatis AspS was determined to a resolution of 2.4 Å.

Original languageEnglish
Article numbere113568
JournalPLoS ONE
Volume9
Issue number11
DOIs
Publication statusPublished - 19 Nov 2014
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2014 Gurcha et al.

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