Biology subjects

Sasidharan, S.

Publications and source records attributed to Sasidharan, S..

4 recordsLinked to original sources

bioRxiv2025

Flow transports extracellular lipid-anchored proteins across the surface of living COS-7 cells

The rapid diffusion of membrane lipids and membrane proteins in living cell plasma membranes demonstrates that the membrane is fluid. However, motion of membrane molecules is inhibited on one side by the cytoskeletal mesh, and on the other by the glycocalyx, a layer of proteoglycans with long polysaccharide chains that covers the membrane surface. A variety of biological fluid flows (including blood circulation, cilia-driven flows, and swimming motion of microorganisms) apply shear stress to cell surfaces. Cell responses to these flows govern important physiological processes such as blood pressure and immune activation. The presence of the glycocalyx is generally thought to shield cell membranes from shear stress that arises from flow. However, here we show that two different proteins, each attached by a lipid anchor to the extracellular membrane surface of living COS-7 cells, formed reversible, cell-wide concentration gradients in the direction of applied flow. Protein redistribution occurred within minutes after we applied shear stress levels commonly found in animal cardiovascular systems. The dynamic and spatial features of these gradients were consistent with passive transport by flow. Passive flow transport could be a general mechanism for spatial organization of membrane proteins. This mechanism may explain protein patterning previously observed on flow-exposed cells, and potentially forms an initial step in flow sensing.

biophysics↗

bioRxiv2025

Shear Stress Induces Concentration Gradient Distributions of Membrane Proteins in Live Cells

Cells sense and respond to fluid shear stress. Cell surfaces are exposed to flow, yet the influence of shear stress on the behavior of plasma membrane proteins remains unclear. Here we show that extracellular flow induces the gradient distribution of cell membrane proteins with increasing concentration toward the downstream direction of the flow. Shear stress at 10-30 dynes/cm2 caused formation of concentration gradients of both GPI-anchored proteins and transmembrane proteins, including integrin{beta}1, E-cadherin and the insulin receptor in Xenopus XTC cells. Using single-molecule live-cell imaging, we found that GPI-anchored T-cadherin molecules are dragged along the direction of flow under shear stress. In addition, shear stress induced concentration gradients of membrane proteins in COS-7 cells and human umbilical vein endothelial cells (HUVECs). Our findings suggest that external flow directly transports membrane proteins, establishing concentration gradients that may contribute to the cellular flow-sensing mechanism.

biophysics↗

bioRxiv2021

A novel innate pathogen sensing strategy involving ubiquitination of bacterial surface proteins

Sensing of pathogens by ubiquitination is critical for maintaining cytosolic sanctity. However, universal ubiquitination targets on bacteria, especially of proteinaceous origin, remain unidentified. Here, we unveil a novel strategy, involving recognition of degron-like motifs for identification of first protein-based ubiquitination substrates on phylogenetically distinct bacteria. Such motifs can form a new class of intra-cytosolic pathogen associated molecular patterns (PAMPs) as their incorporation enables identification of non-ubiquitin targets by host Ub-ligases. We find SCFFBW7 E3-ligase, supported by the regulatory kinase, GSK3{beta}, is crucial for effective pathogen detection and clearance. This may explain the enhanced risk of infections in Chronic Lymphocytic Leukaemia patients bearing FBXW7 mutations. We conclude that exploitation of such ubiquitous pathogen sensing strategy allows conservation of cellular resources and boost anti-microbial immunity. One Sentence SummaryUbiquitination of bacterial surface proteins fosters sensing and clearance of diverse pathogens

microbiology↗

bioRxiv2019

RhoGAP RGA-8 supports morphogenesis in C. elegans by polarizing epithelia through CDC-42

CDC-42 regulation of non-muscle myosin/NMY-2 is required for polarity maintenance in the one-cell embryo of C. elegans. CDC-42 and NMY-2 regulate polarity throughout embryogenesis, but their contribution to later events of morphogenesis are less understood. We have shown that epidermal enclosure requires the GTPase CED-10/Rac1 and WAVE/Scar complex, its effector, to promote protrusions that drive enclosure through the branch actin regulator Arp2/3. Our analysis here of RGA-8, a homolog of SH3BP1/Rich1/ARHGAP17/Nadrin, with BAR and RhoGAP motifs, suggests it regulates CDC-42, so that NMY-2 promotes two events of epidermal morphogenesis: ventral enclosure and elongation. Genetic and molecular data suggest RGA-8 regulates CDC-42, and the CDC-42 effectors WSP-1 and MRCK-1, in parallel to F-BAR proteins TOCA-1 and TOCA-2. The RGA-8-CDC-42-WSP-1 pathway enriches myosin in migrating epidermal cells during ventral enclosure. We propose TOCA proteins and RGA-8 use BAR domains to localize and regenerate CDC-42 activity, thus regulating F-actin levels, through the branched actin regulator WSP-1, and myosin polarity through the myosin kinase MRCK-1. Regulated CDC-42 thus polarizes epithelia, to control cell migrations and cell shape changes of embryonic morphogenesis. SummaryRGA-8, a protein with membrane binding and actin regulatory motifs, promotes embryonic morphogenesis by localizing active CDC-42 in developing epithelia, thus controlling actin and actin motors during cell movements.

developmental biology↗