Biology subjects

Abhishek, S.

Publications and source records attributed to Abhishek, S..

4 recordsLinked to original sources

bioRxiv2022

Metabolic switching and cell wall remodelling of Mycobacterium tuberculosis during bone tuberculosis

Bone tuberculosis is widely characterized by irreversible bone destruction caused by Mycobacterium tuberculosis. Mycobacterium has the ability to adapt to various environmental stresses by altering its transcriptome in order to establish infection in the host. Thus, it is of critical importance to understand the transcriptional profile of M. tuberculosis during infection in the bone environment compared to axenic cultures of exponentially growing M.tb. In the current study, we characterized the in vivo transcriptome of M. tuberculosis within abscesses or necrotic specimens obtained from patients with bone TB using whole genome microarrays in order to gain insight into the M. tuberculosis adaptive response within this host microenvironment. A total of 914 mycobacterial genes were found to be significantly over-expressed and 1688 were repressed (fold change>2; p-value [≤]0.05) in human bone TB specimens. Overall, the mycobacteria displayed a hypo-metabolic state with significant (p[≤]0.05) downregulation of major pathways involved in translational machinery, cellular and protein metabolism and response to hypoxia. However, significant enrichment (p [≤]0.05) of amino-sugar metabolic processes, membrane glycolipid biosynthesis, amino acid biosynthesis (serine, glycine, arginine and cysteine) and accumulation of mycolyl-arabinogalactan-peptidoglycan complex suggests possible mycobacterial survival strategies within the bone lesions by strengthening its cell wall and cellular integrity. Data were also screened for M.tb virulence proteins using Virulent Pred and VICM Pred tools, which revealed five genes (Rv1046c, Rv1230c, DppD, PE_PGRS26 and PE_PGRS43) with a possible role in the pathogenesis of bone TB. Next, an osteoblast cell line model for bone TB was developed allowing for significant intracellular multiplication of M.tb. Interestingly, three virulence genes (Rv1046c, DppD and PE_PGRS26) identified from human bone TB microarray data were also found to be overexpressed by intracellular M. tuberculosis in osteoblast cell lines. Overall, these data demonstrate that M. tuberculosis alters its transcriptome as an adaptive strategy to survive in the host and establish infection in bone. Additionally, the in vitro osteoblast model we describe may facilitate our understanding of the pathogenesis of bone TB. Author SummaryMusculoskeletal tuberculosis is the third most common manifestation of extra-pulmonary tuberculosis and massive bone destruction along with vertebral discs are one of the hallmarks of this disease. Mycobacterium tuberculosis, the causative agent, has the tremendous potential to adapt itself to different host environments due to its ability to alter the expression of genes/proteins belonging to different pathways. This study shows that the mycobacterial infection in bone is driven by the increased expression of genes belonging to cell wall remodelling and DNA damage repair pathways important for its survival. Further data analysis showed that some of these genes are coding for proteins possessing virulence potential that may be essential for survival of M. tuberculosis under such hostile environment of bone. We also developed an in vitro model of bone tuberculosis using an osteoblast cell line and validated the expression of these virulence factors. Identification of such virulence factors in the bone environment by M. tuberculosis may aid to identify new therapeutic targets for bone TB. Further, development of cell line model for bone TB is important to understand some unknown facets of this disease.

microbiology↗

bioRxiv2021

PAR recognition by multiple reader domains of PARP1 allosterically regulates the DNA-dependent activities and independently stimulates the catalytic activity of PARP1

Poly(ADP-ribosyl)ation is predominantly catalyzed by Poly(ADP-ribose) polymerase 1 (PARP1) in response to DNA damage, mediating the DNA repair process to maintain genomic integrity. Single strand (SSB) and double strand (DSB) DNA breaks are bonafide stimulators of PARP1 activity. However, PAR mediated PARP1 regulation remains unexplored. Here, we report ZnF3, BRCT and WGR, hitherto uncharacterized, as PAR reader domains of PARP1. Surprisingly, these domains recognize PARylated protein with a higher affinity compared to PAR but bind with weak or no affinity to DNA breaks as standalone domains. Conversely, ZnF1 and ZnF2 of PARP1 recognize DNA breaks but weakly to PAR. In addition, PAR reader domains, together, exhibit a synergy to recognize PAR or PARylated protein. Further competition binding studies suggest that PAR binding releases DNA from PARP1, and WGR domain facilitates the DNA release. Unexpectedly, PAR showed catalytic stimulation of PARP1 but hampers the DNA-dependent stimulation. Altogether, our work discovers dedicated high-affinity PAR reader domains of PARP1 and uncovers a novel mechanism of allosteric stimulation, but retardation of DNA-dependent activities of PARP1 by its catalytic product PAR. Therefore, our studies can be used as a model to understand the effect of one or more allosteric activators on the regulation of receptors or modular enzyme activities by another allosteric activator.

biophysics↗

bioRxiv2019

UHRF1-SRA recognizes symmetric non-CG methylated DNA through dual-flip out of 5-methyl cytosines

Non-CG DNA methylation (non-mCG) is enriched in the genome of brain neurons and germline cells. Non-mCG is differentially distributed on neuronal X-chromosome in males and females. Accumulation of non-mCG during postnatal brain development correlates with reduced gene expression and inactivation of distal regulatory elements, and allele specific gene regulation. Recently, UHRF1 has been found to contribute to de novo non-CG methylation, however, whether UHRF1 could recognize non-mCG is not known. Here, we have demonstrated through calorimetric measurements that the SRA domain of UHRF1 can recognize mCH and fully-mCHG, types of non-mCG. Furthermore, our ITC binding analyses with methylated CG DNA (mCG) revealed 6-fold decrease in binding affinity for fully-mCG compared to hemi-mCG and, despite symmetrical 5mCs, stoichiometry of 1:1 for UHRF1 SRA binding to fully-mCG indicates UHRF1 may not form stable complex with fully-mCG DNA. In contrast, UHRF1 SRA recognizes fully-mCHG with a stoichiometry of 2:1 protein to DNA duplex, and has tighter binding compared to fully-mCG. Crystal structure of UHRF1 SRA bound to 5mC containing DNA in fully-mCHG context revealed dual flip-out mechanism of 5mC recognition. Altogether, this study indicates that UHRF1 SRA also recognizes non-mCG DNA, besides known hemi-mCG DNA and exhibits contrasting mechanisms for hemi-mCG and fully-mCHG DNA recognition. These findings may open a new window to investigate the biological function of non-CG methylation recognition by the UHRF1.

biophysics↗

bioRxiv2019

Computational insights into mechanism of AIM4-mediated inhibition of aggregation of TDP-43 protein implicated in ALS and evidence for in vitro inhibition of liquid-liquid phase separation (LLPS) of TDP-432C-A315T by AIM4.

TDP-43 is an RNA/DNA-binding protein of versatile physiological functions and it is also implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS) disease in addition to several other implicated proteins such as mutant SOD1 and FUS etc. Cytoplasmic mis-localization, liquid-liquid phase separation (LLPS) due to RNA depletion and aggregation of TDP-43 are suggested to be important TDP-43-toxicity causing mechanisms for the ALS manifestation. So far, therapeutic options for ALS are extremely minimal and ineffective therefore, multi-faceted approaches such as treating the oxidative stress and inhibiting the TDP-43s aggregation are being actively pursued. In our recent study, an acridine imidazolium derivative compound, AIM4, has been identified to have anti-TDP-43 aggregation propensity however, its mechanism of inhibition is not deciphered. In this study, we have utilized computational methods to examine binding site(s) of AIM4 in the TDP-43 structure and have also compared its binding efficiency with several other relevant compounds. We find that AIM4 has a binding site in the C-terminal amyloidogenic core region of amino acids aa: 288-319, which coincides with one of the key residue motifs that could potentially mediate liquid-liquid phase separation (LLPS) of TDP-43. Importantly, alike to the previously reported effects exerted by RNA molecules, we found that AIM4 could also inhibit the in vitro LLPS of a recombinantly purified C-terminal fragment TDP-432C bearing an A315T familial mutation. Antagonistic effects of AIM4 towards LLPS which is believed as the precursor process to the TDP-43s aggregation and the in silico prediction of a binding site of AIM4 on TDP-43 occurring in the same region, assert that AIM4 could be an important molecule for further investigations on TDP-43s anti-aggregation effects with relevance to the ALS pathogenesis.

bioinformatics↗