Pyrazinamide (PZA) is an essential first line
antitubercular drug, which plays a crucial role in
tuberculosis treatment. The PZA, which is considered as a
pro-drug needs an
enzyme of mycobacterial
pyrazinamidase (PZase) for its conversion into an active form
pyrazinoic acid. Further, this active form of PZA inhibits the
ribosomal proteins S1, which facilitates the transfer-
mRNA complex formation throughout the translation. The spontaneous mutations in RpsA have been found to be associated with PZA drug resistance. However, the drug resistance mechanism is still unclear. Furthermore, there is no such information available about the structural dynamics of RpsA
protein because of mutations that confer
Pyrazinoic acid resistance. Moreover, a total of 18 clinical PZA-resistant isolates were investigated and found to be pncAWT, which allowed exploration of the resistance mechanism of RpsA in the mutated state. Samples were repeated for the drug susceptibility testing followed by RpsA gene sequencing. A total of 11 clinical isolates harbored a total of 15 mutations. Almost half of the total strains (7/15) were observed to be in the conserved region of RpsA and known as Mycobacterium tuberculosis C-terminal domain. In the current study, (2/7) mutation T370P (mutant 1) and W403G (mutant 2) were explored to ensure the RpsA resistance mechanism through essential dynamics simulation. The essential dynamics study results revealed that the distal loop mutations drastically altered the conformation of RpsA both in the absence (-) and presence (+) of
pyrazinoic acid drug for two reasons: (1) dramatic alteration or reduction in the binding pattern of
pyrazinoic acid with active site residues observed and (2) a clear image of the opening and closing switching mechanism was seen upon the distal site mutation on nearby 310-helixes beside the
pyrazinoic acid binding site. This switch was found to consistently remain closed only in wild type systems, while it was open in the mutant systems. We called such distance impact an "allosteric effect." The overall mechanistic investigations will provide useful information behind drug resistance for better understanding to manage
tuberculosis.