PARALLEL VIRTUAL SCREENING TO DISCOVER PHYTOCOMPOUNDS TO COUNTER THE RESISTANCE INDUCING EFFECT OF DOUBLE MUTATIONS IN MDR TUBERCULOSIS

Abstract

Drug resistant tuberculosis has threaten all the advances made in tuberculosis control at the global stage in the last few decades. Resistance to quinolone class of drug like Ofloxacin which are being used as a main drug for multiple drug resistant tuberculosis treatment have given rise to cases of extensive drug resistant tuberculosis. DNA gyrase enzyme, essential for DNA replication, translation, and transcription are targeted by quinolones for their bactericidal effect and can be an excellent target for antibacterial drug discovery. Mutations in quinolone resistance determining region of gyrase enzyme, especially in gyrA subunit have conferred resistance to quinolones based drugs. Here we report, a successful application of High Throughput Virtual Screening (HTVS) in identification of a common inhibitor for both wild type and mutant type Mycobacterium DNA gyrase. The most prevalent double mutant strain of tuberculosis that were targeted here is 90V94G, 74S94G and 90V91P DNA gyrase. Chebulinic Acid (CA), a phytocompound obtained from Terminalia chebula was the outcome of present HTVS study as a most potent inhibitor. Also, four more compounds were identified along with CA from a virtual library of 1, 79,299 compounds, but they were less potent compared to CA. CA scored high Extra Precision docking score i.e. -14.63, -16.46, 15.94 and -15.11 against wild type and 90V94G, 74S94G and 90V91P double mutants respectively. The complex was stabilized by multiple H bonding and numerous hydrophobic interaction. This was shown by molecular dynamics simulation studies for a period of 16ns, lower root mean square deviation (RMSD) value and lower root mean square fluctuation (RMSF) value of residues interacting with ligand indicated a formation of stable complexes in all the four cases. The dual inhibition mechanism seems to be pretty effective as CA is causing displacement of catalytic tyr129 residue from 1.6A ْ to 7.3 A ْ from its target phosphate molecule. Also, the CA is causing stearic hindrance to DNA strand at the DNA gate site resulting in loss of cleavage and religation activity of the enzyme. This phytocompound displays desirable quality for carrying forward as a lead compound for drug development.