Biology subjects

Meher, G.

Publications and source records attributed to Meher, G..

3 recordsLinked to original sources

bioRxiv2025

Membrane Interfacial Potential Governs Surface Condensation andFibrillation of α-Synuclein in Neurons

Biomolecular condensates formed via liquid-liquid phase separation (LLPS) are essential for cellular organization. -Synuclein, an amyloidogenic protein linked to Parkinsons Disease (PD), undergoes phase separation at high concentrations, but the influence of lipid membranes on this process remains unclear. Here, combining in vitro reconstitution, cell biology, and simulations, we show that membranous interfaces promote -Synuclein condensation at physiologically relevant sub-critical concentrations ([~]10 nM) without crowding agents. Notably, condensation occurs only on membranes with a specific stoichiometry of lipids, underscoring the role of interfacial potential. These condensates serve as nucleation sites for fibril formation, leading to membrane deformation and rupture. A lattice gas model reveals this behavior as a prewetting-like transition, where an attractive membrane induces local phase separation below the bulk saturation concentration. Indeed altering interfacial potential by lipid composition and membrane depolarization not only drastically changes -Synuclein puncta size and number but also triggers their release from neurons. These findings reveal the crucial role of lipid membrane interfaces in regulating -Synuclein condensation, aggregation and release, shedding light on a potential mechanism of their cell-to-cell propagation during neurodegeneration.

biophysics↗

bioRxiv2025

SB 11285, a Novel Canonical Purine-Pyrimidine Cyclic Dinucleotide, is a Systemically Bioavailable STING Agonist for Cancer Immunotherapy

SummarySB 11285, a novel cell-permeable, canonical 3,5, purine-pyrimidine cyclic dinucleotide has been developed as a potent systemically bioavailable STING agonist currently in clinical trials. The stimulator of Interferon genes (STING) pathway, crucial for cytosolic DNA sensing and innate immunity, presents a promising avenue for novel cancer immunotherapies. Discussed here is the discovery and development of SB11285, a potent activator of the STING pathway, belonging to the canonical class of 3,5 purine-pyrimidine (PuPy) cyclic dinucleotides (CDNs). SB11285 exhibits superior potency and cell permeability compared to non-canonical 2,3-CDNs and demonstrates robust antitumor activity in in vivo syngeneic mouse tumor models, resulting in complete tumor regression, and durable immunological memory. Combination with checkpoint inhibitors and cytotoxic agents further enhances its efficacy. The anti-tumor effects of SB 11285 rely on the induction of CD8+ T cells, activated macrophages, and NK cells in the tumor microenvironment (TME), for efficient tumor killing and fostering profound and durable anti-tumor response. Our findings underscore the potential of functionalized canonical 3,5-Pu-Py CDNs, exemplified by SB11285, as safe and potent STING agonists for multiple routes of administration in cancer therapy. Currently, SB11285 administered intravenously (IV), is undergoing evaluation as the first systemically administered CDN analog in human clinical trials across various tumor types.

immunology↗

bioRxiv2024

Real-time visualization reveals Mycobacterium tuberculosis ESAT-6 disrupts phagosome via fibril-mediated vesiculation

Mycobacterium tuberculosis (Mtb) evades host defense by hijacking and rupturing the phagosome, enabling it to escape to the host cytosol for its survival. ESAT-6, a secreted virulence protein of Mtb, is known to be critical for phagosome rupture. However, the mechanism of ESAT-6-mediated disruption of the phagosomal membrane remains unknown. Using in vitro reconstitution and numerical simulations, we discover that ESAT-6 polymerization remodels and vesiculates phagosomal membrane. In contrast to the pore formation triggered by a bilayer-spanning conformation, we find that the binding of ESAT-6 to the phagosomal membrane is shallow. Such shallow insertion leads to membrane shape transition leading to tubular and bud-like deformations on the membrane in a concentration-dependent manner, facilitated by the reduction in membrane tension and compressibility modulus. Strikingly, our observations suggest that ESAT-6 polymerizes in bulk and on the membrane, both in vitro and in macrophage. Numerical simulations demonstrate that growing fibrils generate both radial and tangential forces causing local remodeling and shape transition of the membrane. Using micropipette aspiration, we quantitatively show that ESAT-6 bound tensed membrane undergoes local changes in membrane curvature and lipid phase separation, also facilitated by the direct contact of the bacteria inside the phagosome. Nonetheless, the vesiculation of the buds is primarily driven by the forces exerted by the polymerization of ESAT-6. Such ESAT-6 mediated vesiculation induces apoptosis and host cell death in a concentration and time-dependent manner that promotes infection. Overall, the findings provide mechanistic insights into the long-standing question of phagosome disruption by Mtb for its escape.

biophysics↗