Biology subjects

BECHARA, C.

Publications and source records attributed to BECHARA, C..

6 recordsLinked to original sources

bioRxiv2026

Divergent activation of the RXFP1 relaxin receptor by protein and small molecule agonists

RXFP1 is an unusual G protein-coupled receptor (GPCR) that mediates physiological adaptations to pregnancy and is a therapeutic target due to its benefits in treatment of fibrosis and heart failure. Protein and small-molecule agonists are currently in mid-stage clinical trials. Here, we present three cryo-electron microscopy structures of RXFP1: ligand-free, bound to the native agonist relaxin-2, and bound to the small-molecule drug candidate AZD5462. These structures show that relaxin-2 engages the receptors ectodomain while AZD5462 binds within transmembrane domain. Together with hydrogen-deuterium exchange mass spectrometry, we show that relaxin-2 induces conformational reorganization of the linker domain into a helical secondary structure. In contrast, AZD5462 stabilizes a unique active conformation capable of inducing {beta}-arrestin recruitment. Both mechanisms are distinctive from the "push-pull" mechanism of glycoprotein hormone receptors. Altogether, our findings define divergent activation mechanisms for protein and small-molecule agonists of RXFP1 and provide structural framework for next-generation drug discovery targeting relaxin receptors and their relatives.

biochemistry↗

bioRxiv2025

A Wnt-induced conformational phospho-switch in DVL3 controls interaction with Frizzled receptors and Wnt/β-catenin signaling

When Wnt ligands bind to Frizzled (FZD) receptors, Dishevelled protein (DVL) gets multiphosphorylated by Casein kinase 1 (CK1). Although, it is well known that DVL phosphorylation relays Wnt signals from receptors to downstream effectors, any mechanistic aspects of DVL function related to phosphorylation remain unresolved. Here, we uncovered a Wnt-induced DVL phospho-switch which is mutually exclusive with FZD engagement. CK1 multiphosphorylation changes dramatically the bulk electrostatics to promote DVL intramolecular coupling between the DEP domain and the adjacent disordered region. A panel of phospho-switch mutants demonstrated a switch-like coupling at the molecular level when a charge threshold is reached. Charge accumulation proximal to DEP proved to be a key functional event required, but not sufficient, for Wnt/{beta}-catenin signaling. Interestingly, the charge-dependent switch-like character of DVL controlled its association with FZD. By integrating findings at different levels, we propose a universal mechanism in which Wnt-induced DVL conformational phospho-switch outcompetes FZD binding and triggers DVL detachment from FZD.

molecular biology↗

bioRxiv2024

Constitutive activity of an atypical chemokine receptor revealed by inverse agonistic nanobodies

Chemokine stimulation of atypical chemokine receptor 3 (ACKR3) does not activate G proteins but recruits arrestins. It is a chemokine scavenger that indirectly influences responses by restricting the availability of CXCL12, an agonist shared with the canonical receptor CXCR4. ACKR3 is upregulated in numerous disorders. Due to limited insights in chemokine-activated ACKR3 signaling, it is unclear how ACKR3 contributes to pathological phenotypes. One explanation may be that high constitutive activity of ACKR3 drives non-canonical signaling through a basal receptor state. Here we characterize the constitutive action of ACKR3 using novel inverse agonistic nanobodies to suppress basal activity. These new tools promote an inactive receptor conformation which decreased arrestin engagement and inhibited constitutive internalization. Basal, non-chemotactic, breast cancer cell motility was also suppressed, suggesting a role for ACKR3 in this process. The basal receptor activity in pathophysiology may provide a new therapeutic approach for targeting ACKR3.

biochemistry↗

bioRxiv2023

TOPOVIBL function in meiotic DSB formation: new insights from its biochemical and structural characterization.

The TOPOVIL complex catalyzes the formation of DNA double strand breaks (DSB) that initiate meiotic homologous recombination, an essential step for chromosome segregation and genetic diversity during gamete production. TOPOVIL is composed of two subunits (SPO11 and TOPOVIBL) and is evolutionarily related to the archaeal TopoVI topoisomerase complex. SPO11 is the TopoVIA subunit orthologue and carries the DSB formation catalytic activity. TOPOVIBL shares homology with the TopoVIB ATPase subunit. TOPOVIBL is essential for meiotic DSB formation, but its molecular function remains elusive, partly due to the lack of biochemical studies. Here, we purified TOPOVIBL{Delta}C25 and characterized its structure and mode of action in vitro. Our structural analysis revealed that TOPOVIBL{Delta}C25 adopts a dynamic conformation in solution and our biochemical study showed that the protein remains monomeric upon incubation with ATP, which correlates with the absence of ATP binding. Moreover, TOPOVIBL{Delta}C25 interacted with DNA, with a preference for some geometries, suggesting that TOPOVIBL senses specific DNA architectures. Altogether, our study identified specific TOPOVIBL features that might help to explain how TOPOVIL function evolved toward a DSB formation activity in meiosis.

molecular biology↗

bioRxiv2023

Conformational dynamics underlying Atypical Chemokine Receptor 3 activation

Atypical Chemokine Receptor 3 (ACKR3) is a G protein-coupled receptor that does not signal through G proteins. It is known as a chemokine scavenger involved in various pathologies, making it an appealing yet intriguing therapeutic target. Indeed, the structural properties that govern ACKR3 functional selectivity and the overall conformational dynamics of ACKR3 activation are poorly understood. Here we combined Hydrogen/Deuterium exchange mass spectrometry (HDX-MS) and molecular dynamics simulations to examine the binding mode and mechanism of action of various small-molecule ACKR3 ligands of different efficacy for {beta}-arrestin recruitment. Our results show that activation or inhibition of ACKR3 is largely governed by intracellular conformational changes of helix 6, intracellular loop 2 and helix 7, while the DRY motif becomes protected during both processes. Moreover, HDX-MS identifies the binding sites and the allosteric modulation of ACKR3 upon {beta}-arrestin 1 binding. In summary, this study highlights the structure-function relationship of small-molecule ligands, the overall activation dynamics of ACKR3, the binding mode of {beta}-arrestin 1 and the atypical dynamic features in ACKR3 that may contribute to its inability to activate G proteins.

biochemistry↗

bioRxiv2021

Discovery and mechanism of action of small molecule inhibitors of ceramidases

Sphingolipid metabolism is tightly controlled by enzymes to regulate essential processes such as energy utilisation and cell proliferation. The central metabolite is ceramide, a pro-apoptotic lipid catabolized by ceramidase enzymes to ultimately produce pro-proliferative sphingosine-1-phosphate. Human ceramidases can be soluble proteins (acid and neutral ceramidase) or integral membrane proteins (alkaline ceramidases). Increasing ceramide levels to increase apoptosis has shown efficacy as a cancer treatment using small molecules inhibiting a soluble ceramidase. Due to the transmembrane nature of alkaline ceramidases, no specific small molecule inhibitors have been reported. Here, we report novel fluorescent substrates (FRETceramides) of ceramidases that can be used to monitor enzyme activity in real-time. We use FRETceramides to discover the first drug-like inhibitors of alkaline ceramidase 3 (ACER3) which are active in cell-based assays. Biophysical characterization of enzyme:inhibitor interactions reveal a new paradigm for inhibition of lipid metabolising enzymes with non-lipidic small molecules. Table of contents summaryUse of synthetic fluorescent ceramide molecules allows the discovery of the first selective drug-like small molecule inhibitors for alkaline ceramidase 3, an intra-membrane enzyme involved in sphingolipid metabolism in health and disease.

biochemistry↗