Biology subjects

Bontems, F.

Publications and source records attributed to Bontems, F..

7 recordsLinked to original sources

bioRxiv2026

Temperature-Dependent Replication and Sensitivity to Innate Immunity of Human Coronavirus HKU1

The human coronavirus HKU1, causing common colds and occasionally severe illness, remains largely uncharacterized because it has not been successfully grown on immortalized cells. Here, we identified Caco2 cells overexpressing TMPRSS2, the HKU1 receptor, as being highly permissive to infection. HKU1 replicated efficiently, formed syncytia and released infectious progeny in these cells at 33{degrees}C, the temperature of the nasal cavity, but was attenuated at 37{degrees}C. Viral entry occurred similarly at both temperatures, but subsequent viral RNA synthesis was enhanced at 33{degrees}C. Released virions displayed higher stability at 33{degrees}C. In Caco2 and primary epithelial nasal cells, HKU1 was sensitive to interferons (IFN), but induction of IFN stimulated genes, such as IFN-Induced Transmembrane Proteins (IFITMs), was delayed at 33{degrees}C. Once expressed, IFITMs comparably inhibited HKU1 fusion at both temperatures. In contrast, SARS-CoV-2 robustly replicated at 37{degrees}C. Thus, cellular permissiveness, innate immunity and viral properties collectively explain why HKU1 replicates more efficiently at nasal temperature. Our results highlight temperature-sensitivity disparities between coronaviruses, likely associated to different pathogenic outcomes.

microbiology↗

bioRxiv2025

Post-translational acylation drives folding and activity of the CyaA bacterial toxin.

Post-translational modifications critically shape protein conformation and function, yet how they regulate bacterial toxins remains elusive. The adenylate cyclase (CyaA) toxin is a major virulence factor of Bordetella pertussis, the causative agent of whooping cough. CyaA is produced as an inactive precursor, proCyaA, which is activated by acylation of two lysine residues within the bacterium. Once acylated and secreted, CyaA invades innate immune cells and disrupts their phagocytic functions. High-resolution structural characterization of CyaA has remained elusive due to its size, multi-domain organization, flexibility, and aggregation propensity. Here, we overcome these challenges and generate the first structural ensembles of both non-acylated and acylated CyaA in solution by combining experimental data with integrative modeling. Coarse-grained molecular dynamics simulations reveal that acylation is critical to stabilize the native fold and to favorably orient CyaA on the target membrane. Overall, our findings reveal how post-translational acylation triggers native folding and provide mechanistic insights into the early steps of host cell intoxication.

biophysics↗

bioRxiv2024

TYPE THREE SECRETION SYSTEM-INDUCED MECHANOPORATION OF VACUOLAR MEMBRANES

SO_SCPLOWUMMARYC_SCPLOWEndomembrane breaching is a crucial strategy employed by intracellular pathogens enclosed within vacuoles to access the nutrient-rich cytosol for intracellular replication. While bacteria use various mechanisms to compromise host membranes, the specific processes and factors involved are often unknown. Shigella flexneri, a major human pathogen, accesses the cytosol relying on the Type Three Secretion System (T3SS) and secreted effectors. Using in-cell correlative light and electron microscopy, we tracked the sequential steps of Shigella host cell entry. Moreover, we captured the T3SS, which projects a needle from the bacterial surface, in the process of puncturing holes in the vacuolar membrane. This initial puncture ensures disruption of the vacuolar membrane. Together this introduces the concept of mechanoporation via a bacterial secretion system as a crucial process for bacterial pathogen-induced membrane damage. GO_SCPLOWRAPHICALC_SCPLOW AO_SCPLOWBSTRACTC_SCPLOW O_FIG O_LINKSMALLFIG WIDTH=199 HEIGHT=200 SRC="FIGDIR/small/613840v1_ufig1.gif" ALT="Figure 1"> View larger version (54K): org.highwire.dtl.DTLVardef@1669028org.highwire.dtl.DTLVardef@8259cborg.highwire.dtl.DTLVardef@1d522caorg.highwire.dtl.DTLVardef@1df0f2d_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2024

Structures of the Foamy virus fusion protein reveal an unexpected link with the F protein of paramyxo- and pneumoviruses

Foamy viruses (FVs) constitute a subfamily of retroviruses. Their envelope glycoprotein (Env) drives the merger of viral and cellular membranes during entry into cells. The only available structures of retroviral Envs are those from human and simian immunodeficiency viruses from the subfamily of orthoretroviruses, which are only distantly related to the FVs. We report here the cryo-EM structures of the FV Env ectodomain in the pre- and post-fusion states, which demonstrate structural similarity with the fusion protein (F) of paramyxo- and pneumoviruses, implying an evolutionary link between the two viral fusogens. Based on the structural information on the FV Env in two states, we propose a mechanistic model for its conformational change, highlighting how the interplay of its structural elements could drive the structural rearrangement. The structural knowledge on the FV Env now provides a framework for functional investigations such as the FV cell tropism and molecular features controlling the Env fusogenicity, which can benefit the design of FV Env variants with improved features for use as gene therapy vectors.

microbiology↗

bioRxiv2023

An original potentiating mechanism revealed by the cryoEM structures of the human α7 nicotinic receptor in complex with nanobodies

The human 7 nicotinic receptor is a pentameric channel mediating cellular and neuronal communication. It has attracted considerable interest to design ligands for the treatment of neurological and psychiatric disorders. To develop a novel class of 7 ligands, we recently generated two nanobodies named E3 and C4 acting as positive and silent allosteric modulators respectively. Here, we solved the cryo-EM structures of the nanobody-receptor complexes. E3 and C4 bind to a common epitope involving two subunits at the apex of the receptor. They form by themselves a symmetric pentameric assembly that extends the extracellular domain. Unlike C4, the binding of E3 drives an active or desensitized conformation in the absence of orthosteric agonist, and mutational analysis shows a key contribution of a N-linked sugar moiety in mediating E3 potentiation. The nanobody E3, by remotely controlling the global allosteric conformation of the receptor, implements an original mechanism of regulation which opens new avenues for drug design.

neuroscience↗

bioRxiv2021

The dengue virus NS1 protein conveys pro-inflammatory signals by docking onto human high-density lipoproteins

The nonstructural NS1 protein is a virulence factor secreted by dengue virus (DENV)-infected cells. NS1 is known to alter the complement system, activate immune cells and perturb endothelial barriers. Here we show that pro-inflammatory signals are triggered by a high affinity complex formed between NS1 and human high-density lipoproteins (HDL). Electron microscopy images of the NS1-HDL complexes show spherical HDL particles with rod-shaped NS1 protrusions on their surface. These complexes are readily detectable in the plasma of hospitalized dengue patients using anti-apolipoprotein A-I (ApoA-I) antibodies specific of the HDL moiety. The functional reprogramming of HDL particles by the NS1 protein as a means to exacerbate systemic inflammation during DENV infection provides a new paradigm linking the human lipoprotein network to dengue pathogenesis.

microbiology↗

bioRxiv2020

Structural and dynamic characterization of the C-terminal tail of ErbB2: disordered but not random

ErbB2 (or HER2) is a receptor tyrosine kinase overexpressed in some breast cancers, associated with poor prognosis. Treatments targeting the receptor extracellular and kinase domains have greatly improved disease outcome in the last twenty years. In parallel, the structures of these domains have been described, enabling better mechanistic understanding of the receptor function and targeted inhibition. However, ErbB2 disordered C-terminal cytoplasmic tail (CtErbB2) remains very poorly characterized in terms of structure, dynamics and detailed functional mechanism. Yet, it is where signal transduction is triggered, via phosphorylation of tyrosine residues, and carried out, via interaction with adaptor proteins. Here we report the first description of ErbB2 disordered tail at atomic resolution, using NMR and SAXS. We show that although no part of CtErbB2 has any stable secondary or tertiary structure, it has around 20% propensity for a N-terminal helix that is suspected to interact with the kinase domain, and many PPII stretches distributed all along the sequence, forming potential SH3 and WW domains binding sites. Moreover, we identified a long-range transient contact involving CtErbB2 termini. These characteristics suggest new potential mechanisms of auto-regulation and protein-protein interaction. SIGNIFICANCEWe report here the first description of the receptor tyrosine kinase ErbB2 disordered tail (CtErbB2) at atomic resolution, using NMR and SAXS. We show that although CtErbB2 exhibits no stable structure, it does exhibit partial secondary and tertiary structures likely important for its function. These structural elements are consistent with an active role of the C-terminal tail in the regulation of the receptors activity, thanks to the presence of preformed structures for intramolecular interactions, as well as long-range contacts modulating accessibility of those sites and proline interaction sites distinct from the main tyrosine sites. Together, those results reinforce the view that disordered tails of receptors are more than random anchors for partners.

biophysics↗