Biology subjects

SARKAR, D.

Publications and source records attributed to SARKAR, D..

3 recordsLinked to original sources

bioRxiv2025

A repressor co-regulatory network integrates iron acquisition to mycobacterial stress tolerance

Growing evidence suggests that controlled regulation of iron (Fe) uptake is essential for mycobacterial survival and proliferation in the host. In this study, we discovered the mechanism that links mycobacterial Fe acquisition to intra-bacterial redox environment via the phoP locus. Remarkably, regulated expression of the major Fe storage protein encoding gene bfrB determines bacterial tolerance to oxidative stress and intracellular survival of the pathogen. Transcriptomic analysis coupled with in vivo DNA binding studies uncover a distinct IdeR-independent regulation, which utilizes Lsr2 and virulence regulator PhoP to modulate transcriptional control of bfrB via recruitment of both the regulators. A striking inhibition of Lsr2 binding to the bfrB promoter in a phoP-KO mutant, attributable to Lsr2-PhoP protein-protein interaction, provides the most fundamental biological insight. Building on these results, we proposed a model suggesting how Lsr2-PhoP interaction (or lack thereof) contributes to repression and/or stress-specific activation of bfrB expression. Collectively, these results uncover a key mechanism linking Fe acquisition and oxidative stress response of mycobacteria, and have significant implications on the intracellular survival of the pathogen.

microbiology↗

bioRxiv2023

Dual functioning by the PhoR sensor is a key determinant to Mycobacterium tuberculosis virulence

PhoP-PhoR empowers M. tuberculosis to adapt to diverse environmental conditions, and remains essential for virulence. Although PhoP and PhoR have been structurally characterized, the signal(s) that this TCS responds to remains unknown. In this study, we show that PhoR is a sensor of acidic pH/high salt conditions, which activate PhoP via phosphorylation. Transcriptomic studies uncover that acidic pH-inducible expression of PhoP regulon is significantly inhibited in a PhoR-deleted M. tuberculosis. Using genome-wide screening we further identify a non-canonical mechanism of PhoP phosphorylation by the sensor kinase PrrB. To investigate how phosphorylation of PhoP is regulated, we discovered that PhoR functions as a phosphatase. Our results identify the motif/residues responsible for contrasting kinase/phosphatase dual functioning of PhoP, and collectively determine the homeostatic regulation of intra-mycobacterial P~PhoP which controls the final output of PhoP regulon. Together, these data uncover that PhoR plays a central role in mycobacterial adaptation to low pH conditions within the host macrophage phagosome. Consistent with these results a PhoR-deleted M. tuberculosis remains significantly attenuated in macrophages and animal models.

microbiology↗

bioRxiv2021

Molecular connectivity between extra-cytoplasmic sigma factors and PhoP accounts for integrated mycobacterial stress response

The main purpose of this study is to understand how mycobacteria can sense numerous stress conditions and mount an appropriate stress response. Recent studies suggest that at low pH M. tuberculosis encounters reductive stress, and in response, modulates redox homeostasis by utilizing the phoPR regulatory system. However, the mechanism of integrated regulation of stress response remains unknown. To probe how PhoP contributes to redox stress response, we find that a PhoP-depleted M. tuberculosis shows a significantly enhanced susceptibility to redox stress relative to the WT bacilli. In keeping with these results, PhoP was shown to contribute to mycothiol redox state. Because SigH, one of the alternative sigma factors of mycobacteria, is known to control expression of redox inducible genes, we probed whether previously-reported PhoP-SigH interaction accounts for mycobacterial redox stress response. We had shown that under acidic conditions PhoP functions in maintaining pH homeostasis via its interaction with SigE. In striking contrast, here we show that under redox stress, direct recruitment of SigH, but not PhoP-SigH interaction, controls expression of mycobacterial thioredoxin genes, a major mycobacterial anti-oxidant system. Together, these unexpected results uncover novel stress-specific enhanced or reduced interaction events of sigma factors and PhoP, as the underlying mechanisms of an adaptive programme, which couples low pH conditions and mycobacterial thiol redox homeostasis. SignificanceM. tuberculosis encounters reductive stress under acidic pH. To investigate the mechanism of integrated stress response, we show that PhoP plays a major role in mycobacterial redox stress response. We observed a significant correlation between phoP-dependent and redox-active expression of thioredoxin genes, a major mycobacterial antioxidant system. Further probing on functioning of regulators reveals that while PhoP controls pH homeostasis via its interaction with SigE, direct recruitment of SigH, but not PhoP-SigH interaction, controls expression of thioredoxin genes. These strikingly contrasting results showing enhanced PhoP-SigE interaction under acidic pH and reduced PhoP-SigH interaction under redox conditions, uncover the underlying novel mechanism of mycobacterial adaptive program, coupling low pH with maintenance of redox homeostasis.

microbiology↗