Biology subjects

Grelard, A.

Publications and source records attributed to Grelard, A..

6 recordsLinked to original sources

bioRxiv2026

A bacterial lipid triggers membrane mechanosensing immunity in Arabidopsis

The plant immune system engages cell-surface receptors that detect microbe-associated molecular patterns to initiate pattern-triggered immunity (PTI), and intracellular receptors that sense microbe-secreted effectors to activate effector-triggered immunity (ETI). Whether additional modes of microbial detection exist remains unclear. Here, we define membrane mechanosensing immunity (MSI), a third layer of immune signaling. A bacterial lipid, the main diffusible signal factor (DSF) from Xanthomonas campestris pv. campestris, acts as a membrane-active molecule that alters plasma membrane biophysical properties, activates Mechanosensitive Channel of Small Conductance (MscS)-like (MSL)-dependent immune signaling, and triggers a broad transcriptional reprogramming that overlaps with PTI and ETI. MSI modulates PTI signaling and requires both PTI and ETI components for effective disease resistance. These findings establish the sensing of metabolite-induced membrane perturbations as a mechanism of microbial detection.

plant biology↗

bioRxiv2025

Membrane partition and structural reorganization induced by anti-psychotics with distinct clinical profiles

Antipsychotics (APs) are used in the treatment of severe mental disorders. Their mechanism of action involves interaction with multiple brain targets, notably the dopamine D2 receptors (D2R), where they compete with dopamine. Due to their lipophilic nature, APs also partition and accumulate in lipid membranes, particularly around the D2R and in synaptic vesicles. When intercalated into brain membranes, APs slowly accumulate and act as a reservoir, allowing their rapid release on demand to modulate neurotransmitter signaling. They also modify the physicochemical and mechanical properties of the lipid bilayer. These modifications can subsequently affect the conformational changes of embedded membrane proteins like the D2R. The present study investigated two major APs with different pharmacological and clinical profiles: chlorpromazine, which exerts its clinical activity mainly through a strong antagonistic action at the D2R, and clozapine, the weakest D2R antagonist of all APs. Surprisingly, although D2R antagonism is usually associated with AP potency, clozapine has repeatedly demonstrated clinical superior efficacy to all APs and is therefore recommended for treatment-resistant schizophrenia. The current work aims to extend the classical AP receptor mediated paradigmatic mode of action to their potential and unique membrane remodeling properties by thoroughly comparing their partitioning and impact on the physicochemical properties of the lipid membrane. Lipid model membranes mimicking synaptic vesicles have been investigated using a combination of several biophysical methods. The study aims to determine how the partitioning of the two APs modifies membrane order, phase transition, thickness, elasticity, phase separation, membrane integrity and charge. Differences have been demonstrated between these two compounds, which may further differ both over time as they accumulate as well as depending on their pre- or post-synaptic location.

biophysics↗

bioRxiv2024

CapP mediates the structural formation of biofilm-specific pili in the opportunistic human pathogen Bacillus cereus

Polymeric proteinaceous filaments are structural scaffolds that diversify the functionality of the bacterial extracellular matrix. Here, we report a previously uncharacterized bacterial factor called bc1280 that is exclusive to B. cereus group and indispensable for the establishment of a biofilm lifestyle. We propose that BC1280 is an essential chaperone for the assembly of the filamentous platform that tightly controls the polymerization of heteropili containing CalY and TasA as major subunits in a concentration-dependent manner. Additionally, BC1280 modulates the expression of EPS via an uncharacterized pathway that is activated by a protease and an ECF-type sigma factor. The pilus biogenesis system described in this work highlights the complexity of extracellular matrix assembly in B. cereus and introduces a singular three-part structuration mechanism during biofilm formation and maturation. Graphical abstractDuring the process of biofilm formation in B. cereus, TasA, CapP, and CalY serve as the main components, in addition to other factors, ensuring that the extracellular matrix correctly assembles. The three proteins are produced and processed by the signal peptidase SipW and subsequently secreted through the Sec pathway in an unfolded conformation. At early biofilm formation stages, CapP is initially present at low levels, associates with the cell wall and is secreted into the ECM where it interacts with unfolded subunits of CalY, facilitating CalY folding and initiating fibril growth. CalY serves as a nucleator for incorporating TasA subunits into the pilus, forming TasA-CalY heteropolymers. Once the ECM scaffold is established, CapP levels increase, forming stable complexes with CalY that prevent its folding and arrest filament growth. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=142 SRC="FIGDIR/small/582368v2_ufig1.gif" ALT="Figure 1"> View larger version (55K): org.highwire.dtl.DTLVardef@df9d9dorg.highwire.dtl.DTLVardef@e4b712org.highwire.dtl.DTLVardef@1af2421org.highwire.dtl.DTLVardef@16d02c7_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2023

Cyclo(Pro-Tyr) elicits conserved cellular damage in fungi by targeting the ATPase Pma1 in plasma membrane domains

Bioactive metabolites play a crucial role in shaping interactions among diverse organisms. In this study, we identified cyclo(Pro-Tyr), a metabolite produced by Bacillus velezensis, as a potent inhibitor of Botrytis cinerea and Caenorhabditis elegans, two potential cohabitant eukaryotic organisms. Based on our investigation, cyclo(Pro-Tyr) disrupts plasma membrane polarization, induces oxidative stress and increases membrane fluidity, which compromises fungal membrane integrity. These cytological and physiological changes induced by cyclo(Pro-Tyr) may be triggered by the destabilization of membrane microdomains containing the [H+]ATPase Pma1. In response to cyclo(Pro-Tyr) stress, fungal cells activate a transcriptomic and metabolomic response, which primarily involves lipid metabolism and Reactive Oxygen Species (ROS) detoxification, to mitigate membrane damage. This similar response occurs in the nematode C. elegans, suggesting that cyclo(Pro-Tyr) universally targets eukaryotic cellular membranes.

microbiology↗

bioRxiv2020

Purification, characterization and influence on membrane properties of the plant-specific sphingolipids GIPC

The plant plasma membrane (PM) is an essential barrier between the cell and the external environment. The PM is crucial for signal perception and transmission. It consists of an asymmetrical lipid bilayer made up of three different lipid classes: sphingolipids, sterols and phospholipids. The most abundant sphingolipids in the plant PM are the Glycosyl Inositol Phosphoryl Ceramides (GIPCs), representing up to 40% of total sphingolipids, assumed to be almost exclusively in the outer leaflet of the PM. In this study, we investigated the structure of GIPCs and their role in membrane organization. Since GIPCs are not commercially available, we developed a protocol to extract and isolate GIPC-enriched fractions from eudicots (cauliflower and tobacco) and monocots (leek and rice). Lipidomic analysis confirmed the presence of different long chain bases and fatty acids. The glycan head groups of the different GIPC series from monocots and dicots were analysed by GC-MS showing different sugar moieties. Multiple biophysics tools namely Langmuir monolayer, {zeta}-Potential, light scattering, neutron reflectivity, solid state 2H-NMR and molecular modelling were used to investigate the physical properties of the GIPCs, as well as their interaction with free and conjugated phytosterols. We showed that GIPCs increase the thickness and electronegativity of model membranes, interact differentially with the phytosterols species and regulate the gel-to-fluid phase transition during temperature variations.

plant biology↗

bioRxiv2020

Emergence of stealth polymorphs that escape α-synuclein amyloid monitoring, take over and acutely spread in neurons

The conformational strain diversity characterizing -synuclein (-syn) amyloid fibrils is possibly at the origin of the different clinical presentations of synucleinopathies. Experimentally, various -syn fibril polymorphs have been obtained from distinct fibrillization conditions by altering the medium constituents and were selected by amyloid monitoring using the probe Thioflavin T (ThT). We report here that besides classical ThT positive products, fibrillization in saline simultaneously gives rise to competing fibril polymorphs that are invisible to ThT (stealth polymorphs), and that can take over. Due to competition, spontaneous generation of such stealth polymorphs bears on the apparent fibrillization kinetics and on the final plateau values. Their emergence has thus been ignored so far or mistaken for fibrillization inhibitions/failures. Compared to their ThT-positive counterparts, and as judged from their chemical shift resonances fingerprint, these new stealth polymorphs present a yet undescribed atomic organization and show an exacerbated propensity (approx. 20-fold) towards self-replication in cortical neurons. They also trigger a long distance synucleinopathic spread along nigro-striatal projections in vivo. In order to rapidly screen fibrillization products for the presence of such stealth polymorphs, we designed a simple multiplexed assay that can be easily and rapidly operated. This assay allows us to demonstrate the sustainability of the conformational replication of these novel and particularly invasive strains. It should also be of help to avoid erroneous upstream interpretations of fibrillization rates based on sole ThT, and to expedite further structural and functional characterization of stealth amyloid assemblies. One Sentence Summarystealth -synuclein fibrils take over

neuroscience↗