The impact of Mycobacterium tuberculosis gyrB point mutations on 6-fluoroquinolones resistance profile: in silico mutagenesis and structure-based assessment

Abstract

Despite the efficiency of 6-fluoroquinolone (6-FQ) antibacterials in fighting tuberculosis (TB), the daily reports related to different forms of quinolone-caused “acquired resistance” in Mycobacterium tuberculosis are becoming rather frequent. Alongside the extensively reported mutations targeting predominantly the quinolone resistance-determining region (QRDR) of the gyrA subunit, some recent studies are pointing out the emergence of gyrB point mutations contributing to the M. tuberculosis resistance as well. To clarify the impact of gyrB alterations on 6-FQs resistance, in silico mutagenesis and structure-based methodology were proficiently employed. Three M. tuberculosis single point gyrB mutants (N473T_mod, T474P_mod, and E475V_mod) based on the recently available structural information were developed. The constructed mutant models were utilized as a starting point for performing molecular docking calculations on a set of 145 6-FQs with determined biological activity values, while their resistance profiles (identification of active/inactive 6-FQs) were evaluated relative to that of the wild-type model. This profiling methodology suggested the following order of resistance degree for our models (N473T_mod > T474P_mod > E475V_mod > 3K9F_mod) which was additionally confirmed by molecular docking of a set of pre-selected 48 combinatorially-generated 6-FQ hits. Furthermore, we identified several attractive substructural fragments that could aid the development of novel 6-FQ antibacterials with possible enhanced anti-mycobacterial activity against diverse M. tuberculosis gyrB mutant strains.