Biology subjects

Dolai, S.

Publications and source records attributed to Dolai, S..

4 recordsLinked to original sources

bioRxiv2026

Leishmania major targets macrophage Syntaxin-2 to impair phagolysosome biogenesis and promote intracellular survival

Macrophages destroy pathogens by engulfing them into phagosomes that mature into degradative phagolysosomes via lysosome fusion. Leishmania parasites subvert this antimicrobial pathway to establish intracellular infection and cause leishmaniasis. We previously identified the SNARE protein syntaxin-2 (Stx2) as a promoter of phagolysosome biogenesis that simultaneously limits particle binding and uptake. Consistent with this dual role, Stx2-depleted macrophages (Stx2-KD) show enhanced binding and internalization of Leishmania major. Stx2-KD macrophages also sustain higher intracellular parasite loads. We find that L. major actively targets macrophage Stx2 by selectively depleting Stx2 from phagosomes through its virulence metalloprotease GP63. Phagosomes containing GP63-deficient L. major retain Stx2 and acquire increased levels of lysosomal hydrolases and v-ATPase, restoring degradative capacity. In BALB/c mice, L. major infection markedly reduces Stx2 in infected tissues in a GP63-dependent manner. Collectively, our findings identify GP63-mediated Stx2 depletion as a key virulence strategy of L. major, positioning the GP63-Stx2 axis as a promising therapeutic target for leishmaniasis.

Cell Biology↗

bioRxiv2024

Syntaxin-2 inhibits phagocytic uptake but promotes phagolysosome formation in macrophages

Phagocytosis engulfs receptor-bound particles by structuring phagocytic cups that expand to form phagosome vesicles. Phagosomes fuse with endosomes and lysosomes to gradually mature into acidic, hydrolase-enriched phagolysosomes for content degradation. While an essential cellular process for eliminating unwanted substances to secure host defense and organismal homeostasis, defective or uncontrolled phagocytosis can be detrimental. Here, we report syntaxin-2 (Stx2), a poorly characterized SNARE in phagocytes, defines the course of macrophage phagocytosis by coordinating cell surface receptor density, phagocytic cup expansion, and phagosome maturation. Stx2 is expressed on the plasma membrane, phagosomes, early endosomes, and to some extent on recycling endosomes, late endosomes and VAMP4-positive compartments. Stx2 knockdown (Stx2-KD) augments engagement and uptake of IgG-opsonized particles by enhanced surface expression of Fc receptors (FcR) and efficient expansion of phagocytic cups. These events are driven by increased recycling of FcR, and enhanced delivery of early endosomes and VAMP4-positive post-Golgi compartments to phagocytic cups. Interestingly, Stx2-KD macrophages exhibit reduced secretion of pro-cathepsins with concomitant increase in lysosome content. However, Stx2 depletion prevents phagosome coalescence with late endosomes and lysosomes to impair maturation by depleted acquisition of cathepsins and reduced acidification. Consequently, macrophages depleted of Stx2 manifest uncontrolled uptake of IgG-opsonized Escherichia coli and impaired digestion resulting in increased bacterial load. Collectively, we uncovered a previously unknown role of Stx2 as a critical balancer of phagocytic uptake and phagolysosomal clearance in macrophages, suggesting that it could be an attractive target for modulation of phagocytosis plasticity and to control aberrant phagocytosis.

cell biology↗

bioRxiv2021

Drivers and Determinants of Strain Dynamics Following Faecal Microbiota Transplantation

Faecal microbiota transplantation (FMT) is an efficacious therapeutic intervention, but its clinical mode of action and underlying microbiome dynamics remain poorly understood. Here, we analysed the metagenomes associated with 142 FMTs, in a time series-based meta-study across five disease indications. We quantified strain-level dynamics of 1,089 microbial species based on their pangenome, complemented with 47,548 newly constructed metagenome-assembled genomes. Using subsets of procedural-, host- and microbiome-based variables, LASSO-regularised regression models accurately predicted the colonisation and resilience of donor and recipient microbes, as well as turnover of individual species. Linking this to putative ecological mechanisms, we found these sets of variables to be informative of the underlying processes that shape the post-FMT gut microbiome. Recipient factors and complementarity of donor and recipient microbiomes, encompassing entire communities to individual strains, were the main determinants of individual strain population dynamics, and mostly independent of clinical outcomes. Recipient community state and the degree of residual strain depletion provided a neutral baseline for donor strain colonisation success, in addition to inhibitive priority effects between species and conspecific strains, as well as putatively adaptive processes. Our results suggest promising tunable parameters to enhance donor flora colonisation or recipient flora displacement in clinical practice, towards the development of more targeted and personalised therapies.

microbiology↗

bioRxiv2018

Apolipoprotein E interacts with amyloid-β oligomers via positively cooperative multivalent binding

Interaction of apolipoprotein E (apoE) isoforms with amyloid-{beta} (A{beta}) peptides is considered a critical determinant of the progression of Alzheimers disease. However, molecular mechanism of the apoE-A{beta} interaction is poorly understood. Here we characterize the nature of the apoE-A{beta} complexes and identify the region of apoE that interacts with A{beta}. We have prepared three distinct fragments of apoE4, viz., the N-terminal fragment (NTF), hinge domain fragment (HDF) and C-terminal fragment (CTF) to compare its interactions with A{beta}. Kinetics of aggregation of A{beta} is delayed dramatically in presence of low, substoichiometric concentrations of both NTF and CTF in lipid-free, as well as, in lipidated forms. Effect of HDF is found to be small. Strong inhibition by NTF and CTF at substoichiometric concentrations indicate interactions with the intermediates or the oligomers of A{beta}. Kinetics of Forster Resonance Energy Transfer (FRET) between full-length apoE4 labeled with EDANS at positions 62, 139, 210, 247, and 276 and tetramethylrhodamine (TMR)-labeled A{beta} further support involvement of multiple regions of apoE in the interactions. Since the interactions involve intermediates of A{beta} quantitative evaluation of the binding affinities are not feasible. Hence we employed a competitive binding assay to examine whether the N- and C-terminal domains interact cooperatively. Addition of unlabeled full-length apoE eliminates the FRET between EDANS-NTF + EDANS-CTF and TMR-A{beta} almost completely but not vice versa. Furthermore, full-length apoE but not the equimolar mixture of the fragments could displace the already bound EDANS-apoE molecules from the complexes. Therefore, binding affinity of the A{beta} oligomers to the intact full-length apoE is much higher than the affinity to the domains when mixed together as fragments. Thus, our results indicate that apoE-A{beta} complex formation is mediated by positively cooperative multivalent binding between the multiple sites on apoE and the oligomeric forms of A{beta}.

biochemistry↗