SummaryProtein tyrosine kinases and tyrosine phosphatases from several bacterial pathogens have been shown to act as virulence factors by modulating the phosphorylation and dephosphorylation of host proteins. The identification and characterization of two tyrosine phosphatases namely MptpA and MptpB from Mycobacterium tuberculosis has been reported earlier.MptpB is secreted by M. tuberculosis into extracellular mileu and exhibits a pH optimum of 5.6, similar to the pH of the lysosomal compartment of the cell. To determine the role of MptpB in the pathogenesis of M. tuberculosis , we constructed a mptpB mutant strain by homologous recombination and compared the ability of parent and the mutant strain to survive intracellularly. We show that disruption of the mptpB gene impairs the ability of the mutant strain to survive in activated macrophages and guinea pigs but not in resting macrophages suggesting the importance of its role in the host-pathogen interaction. Infection of guinea pigs with the mutant strain resulted in a 70-fold reduction in the bacillary load of spleens in infected animals as compared with the bacillary load in animals infected with the parental strain. Upon reintroduction of the mptpB gene into the mutant strain, the complemented strain was able to establish infection and survive in guinea pigs at rates comparable to the parental strain. These observations demonstrate a role of MptpB in the pathogenesis of M. tuberculosis .

The devR-devS two-component system of Mycobacterium tuberculosis was identified earlier and partially characterized in our laboratory. A devR: :kan mutant of M. tuberculosis was constructed by allelic exchange. The devR mutant strain showed reduced cell-tocell adherence in comparison to the parental strain in laboratory culture media. This phenotype was reversed on complementation with a wild-type copy of devR. The devR mutant and parental strains grew at equivalent rates within human monocytes either in the absence or in the presence of lymphocytic cells. The expression of DevR was not modulated upon entry of M. tuberculosis into human monocytes. However, guinea pigs infected with the mutant strain showed a significant decrease in gross lesions in lung, liver and spleen ; only mild pathological changes in liver and lung; and a nearly 3 log lower bacterial burden in spleen compared to guinea pigs infected with the parental strain. Our results suggest that DevR is required for virulence in guinea pigs but is not essential for entry, survival and multiplication of M. tuberculosis within human monocytes in vitro. The attenuation in virulence of the devR mutant in guinea pigs together with DevR-DevS being a bona fide signal transduction system indicates that DevR plays a critical and regulatory role in the adaptation and survival of M. tuberculosis within tissues.

The ability of Mycobacterium tuberculosis to persist in a dormant state is a hallmark of tuberculosis. An insight into the expression of mycobacterial proteins will contribute to our understanding of bacterial physiology in vivo. To this end, the expression of FtsZ, Acr and DevR was assessed in the lung granulomas of guinea pigs infected with M. tuberculosis. Antigen immunostaining was then compared with the detection of acid-fast bacilli (AFB) and mycobacterial DNA. Surprisingly, immunostaining for all three antigens was observed throughout the course of infection; maximum expression of all antigens was noted at 20 weeks of infection. The intensity of immunostaining correlated well with the presence of intact bacteria, suggesting that mycobacterial antigens in the extracellular fraction have a short half-life; in contrast to protein, extracellular bacterial DNA was found to be more stable. Immunostaining for bacterial division and dormancy markers could not clearly distinguish between replicating and non-replicating organisms during the course of infection. The detection of Acr and DevR from 4 weeks onwards indicates that the dormancy proteins are expressed from early on in infection. Both antigen staining and DNA detection from intact bacilli were useful for detecting intact mycobacteria in the absence of AFB.

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A novel coronavirus (SARS-CoV2) has caused a major outbreak in humans around the globe, and it became a severe threat to human healthcare than all other infectious diseases. Researchers were urged to discover and test various approaches to control and prevent such a deadly disease. Considering the emergency and necessity, we screened reported antiviral compounds present in the traditional Indian medicinal plants for the inhibition of SARS-CoV2 main protease. In this study, we used molecular docking to screen 41 reported antiviral compounds that exist in Indian medicinal plants and shown amentoflavone from the plant Torreyanucifera with a higher docking score. Furthermore, we performed a 40 ns atomic molecular dynamics simulation and free binding energy calculations to explore the stability of the top five protein–ligand complexes. Through the article, we insist that the amentoflavone, hypericin and Torvoside H from the traditional Indian medicinal plants may be used as a potential inhibitor of SARS-CoV2 main protease and further biochemical experiments could shed light on understanding the mechanism of inhibition by these plant-derived antiviral compounds. Communicated by Ramaswamy H. Sarma