Biology subjects

Gopal, B.

Publications and source records attributed to Gopal, B..

3 recordsLinked to original sources

bioRxiv2021

Particle Uptake Driven Phagocytosis in Macrophages and Neutrophils Enhances Bacterial Clearance

Humans are exposed to numerous synthetic foreign particulates in the form of environmental pollutants and diagnostic or therapeutic agents. Specialized immune cells (phagocytes) clear these particulates by phagocytosing and attempting to degrade them. The process of recognition and internalization of the particulates may trigger changes in the function of phagocytes. Some of these changes, especially the ability of a particle-loaded phagocyte to take up and neutralize pathogens, remains poorly studied. Herein, we demonstrate that the uptake of non-stimulatory cargo-free particles enhances the phagocytic ability of monocytes, macrophages and neutrophils. The enhancement in phagocytic ability was independent of particle properties, such as size or the base material constituting the particle. Additionally, we show that the increased phagocytosis was not a result of cellular activation or cellular heterogeneity but was driven by changes in cell membrane fluidity and cellular compliance. A consequence of the enhanced phagocytic activity was that particulate-laden immune cells neutralize E. coli faster in culture. Moreover, when administered in mice as a prophylactic, particulates enable faster clearance of E. coli and S. epidermidis. Together, we demonstrate that the process of uptake induces cellular changes that favor additional phagocytic events. This study provides insights into using non-stimulatory cargo-free particles to engineer immune cell functions for applications involving faster clearance of phagocytosable particulates.

immunology↗

bioRxiv2020

Nitric oxide-inducible Fe-S cluster biogenesis enables Mycobacterium tuberculosis to persist in mice

The persistence of Mycobacterium tuberculosis (Mtb) is a major problem in managing tuberculosis (TB). Host-generated nitric oxide (NO) is perceived as one of the signals by Mtb to reprogram metabolism and respiration for persistence. However, the mechanisms involved in NO sensing and reorganizing Mtbs physiology are not fully understood. Since NO damages Fe-S clusters of essential enzymes, the mechanism(s) involved in regulating iron-sulfur (Fe-S) cluster biogenesis could help Mtb persist in host tissues. Here, we show that a transcription factor SufR (Rv1460) senses NO via its 4Fe-4S cluster and promotes persistence of Mtb by mobilizing the Fe-S cluster biogenesis system; suf operon (Rv1460-Rv1466). Analysis of anaerobically purified SufR by UV-visible spectroscopy, circular dichroism, and iron-sulfide estimation confirms the presence of a 4Fe-4S cluster. Atmospheric O2 and H2O2 gradually degrade the 4Fe-4S cluster of SufR. Furthermore, electron paramagnetic resonance (EPR) analysis demonstrates that NO directly targets SufR 4Fe-4S cluster by forming a protein-bound dinitrosyl-iron-dithiol complex. DNase I footprinting, gel-shift, and in vitro transcription assays confirm that SufR directly regulates the expression of the suf operon in response to NO. Consistent with this, RNA- sequencing of Mtb{Delta}sufR demonstrates deregulation of the suf operon under NO stress. Strikingly, NO inflicted irreversible damage upon Fe-S clusters to exhaust respiratory and redox buffering capacity of Mtb {Delta}sufR. Lastly, Mtb{Delta} sufR failed to recover from a NO-induced non-growing state and displayed persistence defect inside immune-activated macrophages and murine lungs in a NO-dependent manner. Data suggest that SufR is a sensor of NO that supports persistence by reprogramming Fe-S cluster metabolism and bioenergetics. HighlightsO_LIMycobacterium tuberculosis (Mtb) induces the expression of suf operon for Fe-S cluster biogenesis in response to nitric oxide (NO). C_LIO_LIWe found that a transcription factor SufR senses NO via its 4Fe-4S cluster and regulates the expression of the suf operon for Fe-S cluster biogenesis. C_LIO_LISufR-regulated Fe-S cluster biogenesis confers respiratory and redox features that promote recovery of Mtb from NO stress. C_LIO_LISufR activity is required to support the NO-dependent persistence of Mtb in macrophages and mice. C_LI

microbiology↗

bioRxiv2018

Selectivity among anti-σ factors by Mycobacterium tuberculosis ClpX influences intracellular levels of Extracytoplasmic Function σ factors

Extracytoplasmic Function {sigma} factors that are stress inducible are often sequestered in an inactive complex with a membrane-associated anti-{sigma} factor. M. tuberculosis membrane-associated anti-{sigma} factors have a small stable RNA gene A-like degron for targeted proteolysis. Interaction between the unfoldase, ClpX, and the substrate with an accessible degron initiates energy-dependent proteolysis. Four anti-{sigma} factors with a mutation in the degron provided a set of natural substrates to evaluate the influence of the degron on degradation strength in ClpX-substrate processivity. We note that a point mutation in the degron (XXX-Ala-Ala) leads to an order of magnitude difference in the dwell time of the substrate on ClpX. Differences in ClpX/anti-{sigma} interactions were correlated with change in unfoldase activity. GFP chimeras or polypeptides of identical length with the anti-{sigma} degron also demonstrate degron-dependent variation in ClpX activity. We show that degron-dependent ClpX activity leads to differences in anti-{sigma} factor degradation thereby regulating the release of free {sigma} from the {sigma}/anti-{sigma} complex. M. tuberculosis ClpX activity thus influences changes in gene expression by modulating the cellular abundance of ECF {sigma} factors.\n\nImportanceThe ability of Mycobacterium tuberculosis to quickly adapt to the changing environmental stimuli occurs by maintaining protein homeostasis. Extra-cytoplasmic function (ECF) {sigma} factors play a significant role in coordinating the transcription profile to changes in environmental conditions. Release of the {sigma} factor from the anti-{sigma} is governed by the ClpXP2P1 assembly. M. tuberculosis ECF anti-{sigma} factors have a ssrA-like degron for targeted degradation. A point mutation in the degron leads to differences in ClpX mediated proteolysis and affects the cellular abundance of ECF {sigma}-factors. ClpX activity thus synchronizes changes in gene expression with environmental stimuli affecting M. tuberculosis physiology.

biochemistry↗