Biology subjects

Bhausaheb, A. J.

Publications and source records attributed to Bhausaheb, A. J..

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↗

bioRxiv2024

Direct contact of the bacterial surface induces phase separation in the host phagosome membrane

Mycobacterium tuberculosis (Mtb) establishes intracellular niches by remodeling host membranes into either spacious or compact phagosomes, yet how direct bacterial contact within these distinct compartments facilitates bacterial egress remains unknown. Using fixed cell imaging, in vitro reconstitution of phagosome-like vesicles, and numerical simulations, we uncover that mycobacterial load and its direct contact determines phagosome fate by driving membrane bending, lipid wrapping and phase separation. Low-to-moderate load induces membrane vesiculation, generating compact phagosome-like structures. High bacterial load drives a scaffold-like architecture that primes compartments for rupture via complete lipid phase separation and changes in the membranes bending and area stretch moduli, rendering it more deformable. Notably, physical contact synergizes with the virulence factor ESAT-6, amplifying its membrane-deforming activity to disrupt phagosomal integrity. We propose that mycobacteria actively switch spacious to compact phagosomal states by modulating host membrane mechanics--a process governed by the membrane-to-contact area ratio and proximity to lipid demixing point. These findings reveal a biophysical switch in pathogen-driven membrane remodeling, with broad implications for understanding how intracellular pathogens manipulate host membranes to survive.

biophysics↗

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↗