Année Type Filtrer >

1 […]
Avidity-driven polarity establishment via multivalent lipid-GTPase module interactions
The EMBO journal, 2019, 38,
While Rho GTPases are indispensible regulators of cellular polarity, the mechanisms underlying their anisotropic activation at membranes have been elusive. Using the budding yeast Cdc42 GTPase module, which includes a guanine nucleotide exchange factor (GEF) Cdc24 and the scaffold Bem1, we find that avidity generated via multivalent anionic lipid interactions is a critical mechanistic constituent of polarity establishment. We identify basic cluster (BC) motifs in Bem1 that drive the interaction of the scaffold-GEF complex with anionic lipids at the cell pole. This interaction appears to influence lipid acyl chain ordering, thus regulating membrane rigidity and feedback between Cdc42 and the membrane environment. Sequential mutation of the Bem1 BC motifs, PX domain, and the PH domain of Cdc24 lead to a progressive loss of cellular polarity stemming from defective Cdc42 nanoclustering on the plasma membrane and perturbed signaling. Our work demonstrates the importance of avidity via multivalent anionic lipid interactions in the spatial control of GTPase activation.
2 […]
Molecular mechanisms for the destabilization of model membranes by islet amyloid polypeptide
Biophysical chemistry, 2019, 245, 34-40
Misfolding of human islet amyloid polypeptide (hIAPP) into insoluble aggregates is associated with Type 2 diabetes. It has been suggested that hIAPP toxicity may be due to its accumulation in pancreatic islets, causing membrane disruption and cell permeabilization, however the molecular basis underlying its lipid association are still unclear. Here, we combine solid-state NMR, fluorescence and bright field microscopy to investigate hIAPP - lipid membrane interactions. Real-time microscopy highlights a time-dependent penetration of hIAPP oligomers toward the most buried layers of the lipid vesicles until the membrane disrupts. Deuterium NMR was conducted on liposomes at different hIAPP concentration to probe lipid internal order and thermotropism. The gel-to-fluid phase transition of the lipids is decreased by the presence of hIAPP, and site-specific analysis of the order parameter showed a significant increase of lipid order for the first eight positions of the acyl chain, suggesting a partial insertion of the peptide inside the bilayer. These results offer experimental insight into the membrane destabilization of hIAPP on model membrane vesicles.
3 […]
GRELARD, Axelle; DUFOURC, Erick;
Heat-Triggered Crystallization of Liquid Crystalline Macrocycles Allowing for Conductance Switching through Hysteretic Thermal Phase Transitions
Chemistry-an Asian Journal, 2019, 14, 141-148
A polymesomorphic thermal phase-transition of a macrocyclic amphiphile consisting of aromatic groups and oligoethylene glycol (OEG) chains is reported. The macrocyclic amphiphile exists in a highly-ordered liquid crystal (LC) phase at room temperature. Upon heating, this macrocycle shows phase-transition from columnar-lamellar to nematic LC phases followed by crystallization before melting. Spectroscopic studies suggest that the thermally induced crystallization is triggered by a conformational change at the OEG chains. Interestingly, while the macrocycle returns to the columnar-lamellar phase after cooling from the isotropic liquid, it retains the crystallinity after cooling from the thermally-induced crystal. Thanks to this bistability, conductance switching was successfully demonstrated. A different macrocyclic amphiphile also shows an analogous phase-transition behavior, suggesting that this molecular design is universal for developing switchable and memorizable materials, by means of hysteretic phase-transition processes.
4 […]
LOQUET, Antoine;
Tetrameric Abeta40 and Abeta42 beta-Barrel Structures by Extensive Atomistic Simulations. I. In a Bilayer Mimicking a Neuronal Membrane
The journal of physical chemistry. B, 2019, 123, 3643-3648
The amyloid-beta (Abeta) 42 oligomers are much more toxic than Abeta40 oligomers in Alzheimer's disease. Numerous experiments indicate that toxicity could involve the formation of pores in membranes, but experimental high-resolution structure determination of these pore-forming Abeta oligomers has been impeded by aggregate heterogeneity. Using extensive atomistic simulations, low-resolution data obtained in lipid bilayers, and other theoretical factors, we proposed atomic structures of Abeta40 and Abeta42 beta-barrels in a bilayer mimicking a neuronal membrane. The 3D model, which consists of tetramer subunits, two distinct beta-hairpin motifs and an asymmetric arrangement of eight antiparallel beta-strands, is drastically destabilized for Abeta40 compared to its Abeta42 counterpart. Our computational modeling has several implications in Alzheimer's disease, sheds light on the amyloid pore hypothesis, and explains the higher deleterious property of Abeta42.
5 […]
LAMON, Gaëlle; LOQUET, Antoine;
The extracellular matrix protects Bacillus subtilis colonies from Pseudomonas invasion and modulates plant co-colonization
Nature Communications, 2019, 10,
Bacteria of the genera Pseudomonas and Bacillus can promote plant growth and protect plants from pathogens. However, the interactions between these plant-beneficial bacteria are understudied. Here, we explore the interaction between Bacillus subtilis 3610 and Pseudomonas chlororaphis PCL1606. We show that the extracellular matrix protects B. subtilis colonies from infiltration by P. chlororaphis. The absence of extracellular matrix results in increased fluidity and loss of structure of the B. subtilis colony. The P. chlororaphis type VI secretion system (T6SS) is activated upon contact with B. subtilis cells, and stimulates B. subtilis sporulation. Furthermore, we find that B. subtilis sporulation observed prior to direct contact with P. chlororaphis is mediated by histidine kinases KinA and KinB. Finally, we demonstrate the importance of the extracellular matrix and the T6SS in modulating the coexistence of the two species on melon plant leaves and seeds.
6 […]
HABENSTEIN, Birgit; LOQUET, Antoine;
Structural and Functional Characterization of the Type Three Secretion System (T3SS) Needle of Pseudomonas aeruginosa
Frontiers in Microbiology, 2019, 10,
The type three secretion system (T3SS) is a macromolecular protein nano-syringe used by different bacterial pathogens to inject effectors into host cells. The extracellular part of the syringe is a needle-like filament formed by the polymerization of a 9-kDa protein whose structure and proper localization on the bacterial surface are key determinants for efficient toxin injection. Here, we combined in vivo, in vitro, and in silico approaches to characterize the Pseudomonas aeruginosa T3SS needle and its major component PscF. Using a combination of mutagenesis, phenotypic analyses, immunofluorescence, proteolysis, mass spectrometry, atomic force microscopy, electron microscopy, and molecular modeling, we propose a model of the P aeruginosa needle that exposes the N-terminal region of each PscF monomer toward the outside of the filament, while the core of the fiber is formed by the C-terminal helix. Among mutations introduced into the needle protein PscF, D76A, and P47A/Q54A caused a defect in the assembly of the needle on the bacterial surface, although the double mutant was still cytotoxic on macrophages in a T3SS-dependent manner and formed filamentous structures in vitro. These results suggest that the T3SS needle of P aeruginosa displays an architecture that is similar to that of other bacterial needles studied to date and highlight the fact that small, targeted perturbations in needle assembly can inhibit T3SS function. Therefore, the T3SS needle represents an excellent drug target for small molecules acting as virulence blockers that could disrupt pathogenesis of a broad range of bacteria.
7 […]
MARTINEZ, Denis; LEGRAND, Anthony; LAMBERT, Olivier; BERBON, Mélanie; GRELARD, Axelle; LOQUET, Antoine; HABENSTEIN, Birgit;
Coiled-coil oligomerization controls localization of the plasma membrane REMORINs
Journal of Structural Biology, 2019, 206, 12-19
REMORINs are nanodomain-organized proteins located in the plasma membrane and involved in cellular responses in plants. The dynamic assembly of the membrane nanodomains represents an essential tool of the versatile membrane barriers to control and modulate cellular functions. Nevertheless, the assembly mechanisms and protein organization strategies of nanodomains are poorly understood and many structural aspects are difficult to visualize. Using an ensemble of biophysical approaches, including solid-state nuclear magnetic resonance, cryo-electron microscopy and in vivo confocal imaging, we provide first insights on the role and the structural mechanisms of REMORIN trimerization. Our results suggest that the formation of REMORIN coiledcoil trimers is essential for membrane recruitment and promotes REMORIN assembly in vitro into long filaments by trimer-trimer interactions that might participate in nanoclustering into membrane domains in vivo.
8 […]
BERBON, Mélanie; HABENSTEIN, Birgit; LOQUET, Antoine;
A polymorphic helix of a Salmonella needle protein relays signals defining distinct steps in type III secretion
PLoS biology, 2019, 17, e3000351-e3000351
Type III protein-secretion machines are essential for the interactions of many pathogenic or symbiotic bacterial species with their respective eukaryotic hosts. The core component of these machines is the injectisome, a multiprotein complex that mediates the selection of substrates, their passage through the bacterial envelope, and ultimately their delivery into eukaryotic target cells. The injectisome is composed of a large cytoplasmic complex or sorting platform, a multiring base embedded in the bacterial envelope, and a needle-like filament that protrudes several nanometers from the bacterial surface and is capped at its distal end by the tip complex. A characteristic feature of these machines is that their activity is stimulated by contact with target host cells. The sensing of target cells, thought to be mediated by the distal tip of the needle filament, generates an activating signal that must be transduced to the secretion machine by the needle filament. Here, through a multidisciplinary approach, including solid-state NMR (SSNMR) and cryo electron microscopy (cryo-EM) analyses, we have identified critical residues of the needle filament protein of a Salmonella Typhimurium type III secretion system that are involved in the regulation of the activity of the secretion machine. We found that mutations in the needle filament protein result in various specific phenotypes associated with different steps in the type III secretion process. More specifically, these studies reveal an important role for a polymorphic helix of the needle filament protein and the residues that line the lumen of its central channel in the control of type III secretion.
Antoine Loquet Group Accueil Colloids for Health & Nutrition Mentions légales Group History Members Publications Highlights Lipids in all their states Membrane Proteins & Killer Peptides NMR of Soft Matter Contact NMR of Molecular Assemblies Lectures
Manager Antoine LOQUET


Institut Européen de Chimie et Biologie (IECB)

2 rue Robert Escarpit
33607 Pessac
Tel. : +33 (5) 40 00 30 38

Plan d'accès
informations Mentions légales Dernière mise à jour : 06/01/2016

Le CNRS Université de Bordeaux Institut Polytechnique de Bordeaux