Synthetic quercetin inhibits mycobacterial growth possibly by interacting with DNA gyrase

Abstract

Gyrases are DNA topology modifying enzymes, present only in prokaryotes which make them an attractive target for various antimicrobials. Quercetin, a major flavonoid, is known to inhibit supercoiling activity of DNA gyrase. Docking studies were performed to check the effect of quercetin against DNA gyrase of Mycobacterium smegmatis and Mycobacteirum tuberculosis. The results show that, quercetin effectively binds with the subunit B of DNA gyrase through interaction with residues that are in the Toprim domain of the protein. This domain is found to be very much essential for the cleavage and reunion of DNA. Using resazurin microtitre plate assay, the Minimum Inhibitory Concentration (MIC) of quercetin against both M. smegmatis and M. tuberculosis was found to be 100µg/ml. The effect of quercetin against cytoplasmic membrane integrity of bacilli was assayed by potassium ion loss both in M. smegmatis and M. tuberculosis. The results imply that there is no cytoplasmic membrane damage caused by quercetin. Therefore, we report that DNA gyrase might be a probable target for the quercetin in mycobacterium.