Biology subjects

Raynal, B.

Publications and source records attributed to Raynal, B..

13 recordsLinked to original sources

bioRxiv2026

Deciphering the nucleotide driven kinetic and oligomeric dynamics in IMPDH regulation

Inosine monophosphate dehydrogenase (IMPDH) controls guanine nucleotide biosynthesis. Here, using biochemical and integrative structural biology approaches, we characterize the class II bacterial IMPDH from Burkholderia thailandensis. We demonstrate that MgGTP acts as a direct allosteric inhibitor independently of MgATP, promoting tetramer-to-octamer assembly via the Bateman domain. When both nucleotides are present, the enzyme exhibits a biphasic response: low MgGTP concentrations enhance activity, whereas higher concentrations restore inhibition. Structural analyses reveal distinct octameric conformations and capture a pre-catalytic Michaelis complex with substrates and effectors bound. These findings uncover a regulatory mechanism where the Bateman domain integrates opposing nucleotide signals to dynamically control guanine nucleotide biosynthesis, highlighting IMPDH as a potential antimicrobial target in pathogenic Burkholderia species.

biochemistry↗

bioRxiv2026

Structural insights into the inactive state of the adhesion GPCR ADGRV1

Adhesion G protein-coupled receptors (aGPCRs) are involved in numerous physiological processes, including cell-cell and cell-matrix interactions, and are associated with several human diseases. ADGRV1 is a member of the aGPCR family and plays a significant role in the sensorineural systems. Mutations of ADGRV1 are linked to the Usher syndrome, a genetic disorder causing deafness and blindness in human. However, the molecular mechanisms that control the activity of ADGRV1 remain unclear. In this study, we present the high-resolution cryo-electron microscopy structure of the inactive ADGRV1 receptor in complex with the nanobody RE02, providing detailed insights into its transmembrane domain, intracellular loop conformations and the inactive orthosteric site. Functional cellular assays revealed that ADGRV1 exhibits a weak constitutive activation independent of the tethered agonist peptide, primarily coupling with Gi proteins. These findings suggest that ADGRV1 may employ an alternative activation mechanism, distinct that from other aGPCRs reported so far. Our structural analysis highlights that ADGRV1 does not follow the conventional tethered agonist activation mechanism. This is due to the divergent sequence of its tethered agonist peptide, as well as the lack of residues critical for conformational transitions toward the active state in other aGPCRs. Moreover, the large intracellular loop 3 (ICL3) adopts a closed conformation, tightly packed against the transmembrane region of ADGRV1. This suggests that the ICL3 loop can compete with G-protein binding, ultimately acting as an additional barrier for ADGRV1 activation. Significance StatementAdhesion G protein-coupled receptors (aGPCRs) regulate essential processes such as cell communication and sensory function, yet the mechanisms controlling many family members remain poorly understood. We report the first high-resolution cryo-electron microscopy structure of the human receptor ADGRV1, a protein linked to Usher syndrome, a major genetic cause of deafness and blindness. Structural and functional analyses reveal that ADGRV1 displays weak constitutive signaling and likely operates through an activation mechanism distinct from the canonical tethered agonist model that defines most aGPCRs. Unique structural features, including a closed intracellular loop (ICL3) that may limit G-protein engagement, suggest an alternative regulatory strategy. These findings expand the conceptual framework of aGPCR activation and provide a foundation for understanding ADGRV1 function in sensory physiology and disease.

biochemistry↗

bioRxiv2026

Structural basis of MfpD, a versatile pathogeny protein from the mfp conservon of Mycobacterium tuberculosis

The mfp conservon of Mycobacterium tuberculosis has been associated with fluoroquinolone resistance and encodes five conserved proteins, including the small GTPase MfpB and its regulatory partner MfpD. In this study, we combined phylogenetic, structural, and biophysical approaches to define the molecular basis of MfpD function. MfpD adopts a Roadblock/LC7-like /{beta} fold and forms a stable dimer in solution, with hydrophobic 2-helix interactions stabilizing the interface. Additional biophysical analyses and AlphaFold3 modeling suggest that MfpD may promote GTP hydrolysis by MfpB through a noncanonical Switch I-dependent mechanism. These findings establish the first structural framework for MfpD-MfpB interactions, building on previously identified in vitro catalytic properties and proposing new insights into MfpDs non-catalytic pathogenesis activity of MfpD in macrophages. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=69 SRC="FIGDIR/small/709265v2_ufig1.gif" ALT="Figure 1"> View larger version (21K): org.highwire.dtl.DTLVardef@77b2d2org.highwire.dtl.DTLVardef@7d1908org.highwire.dtl.DTLVardef@f66eeforg.highwire.dtl.DTLVardef@ed159c_HPS_FORMAT_FIGEXP M_FIG GRAPHICAL ABSTRACT C_FIG

biochemistry↗

bioRxiv2026

Bacterial targeting of host paraspeckles uncovers a new SFPQ-based regulation

Nuclear functions are key in protecting cells against infections, yet intracellular pathogens like Legionella pneumophila can exploit these mechanisms to survive. We characterized a L. pneumophila protein, LpDot1, which shares sequence similarity with the eukaryotic catalytic domain of the histone methyltransferase DOT1. Structure determination, together with biochemical and biophysical analyses, revealed that LpDot1 methylates non-histone nuclear proteins, notably the splicing factor proline-glutamine rich protein (SFPQ). Importantly, LpDot1 targets the previously uncharacterized K518, located on an important structural motif of SFPQ, therefore impairing its dimerization in vitro. During infection, L. pneumophila modulates SFPQ abundance and activities in a LpDot1-dependent manner, thereby hijacking paraspeckle organization and the host cell splicing machinery, leading to alternative splice variants of infection related genes such as NF-kB2 and CD45. To our knowledge, this is the first report of a bacterial effector directly modifying paraspeckle dynamics, providing new insight into previously uncharacterized eukaryotic regulatory pathways.

microbiology↗

bioRxiv2025

Activation Mechanism and Structural Assembly of the Mycobacterium tuberculosis ClpP1P2 Protease and Its Associated ATPases.

Supramolecular assemblies are integral to cellular biochemical processes, relying on their dynamic nature to fulfill essential functions. The protease ClpP1P2, paired with ATPase partners ClpC1 or ClpX, is vital for the survival of Mycobacterium tuberculosis (Mtb). While the ClpP1P2 complex requires activation by specific N-blocked dipeptides (e.g., Z-Leu-Leu) to exhibit proteolytic activity in vitro, the mechanism of in vivo activation remains unclear. In this study, we identified novel activators that enabled the structural determination of the ClpC1P1P2 complex, providing insights into its assembly. Furthermore, we discovered that trehalose - a key metabolite and molecular crowding agent in Mtb, significantly enhances the activity of both ClpC1P1P2 and ClpXP1P2 complexes without the need for activating peptides. Analytical ultracentrifugation revealed that trehalose promotes the formation of these active complexes, mimicking intracellular conditions. These findings propose a new model of Clp system activation in vivo, offering promising avenues for therapeutic targeting in tuberculosis treatment. Significance StatementThe proteolytic complex formed by the essential proteins ClpP1 and ClpP2, along with their specific ATP-dependent activators ClpX and ClpC1, has emerged as a highly attractive target for anti-tuberculosis drug development. While previous studies have shown that ClpP1P2 can be activated in vitro by small peptide activators, its in vivo activation mechanism remains unclear. In this study, we identify novel activators and demonstrate that trehalose, a key metabolite in Mycobacterium tuberculosis, enhances ClpC1P1P2 and ClpXP1P2 activity without the need for activating peptides. These findings propose a new model for Clp system activation in Mycobacterium tuberculosis, advancing our understanding of its regulation and potential as a therapeutic target.

biochemistry↗

bioRxiv2024

Incomplete lytic cycle of a widespread Bacteroides bacteriophage leads to the formation of defective viral particles

Advances in metagenomics have led to the identification of new intestinal temperate bacteriophages. However, their experimental characterization remains challenging due to a limited understanding of their lysogenic-lytic cycle and the common lack of plaque formation in vitro. In this study we investigated the hankyphage, a widespread transposable phage of prominent Bacteroides symbionts. Hankyphages spontaneously produced virions in laboratory conditions even in the absence of inducer, but virions did not show any evidence of infectivity. To increase virion production and raise the chances of observing infection events, we identified a master repressor of the hankyphage lytic cycle, RepCHP, whose silencing amplified hankyphage gene expression, enhanced replicative transposition and virion production. However, attempts to infect or lysogenize new host cells with different capsular types remained unsuccessful. Transmission electron microscopy and capsid DNA sequencing revealed an abnormal virion morphology and incomplete DNA packaging of the hankyphage, suggesting that it cannot complete its assembly in laboratory conditions for reasons that are yet to be identified. Still, metavirome and phylogenetic analyses were suggestive of hankyphage horizontal transmission. We could also detect the activity of diversity-generating retroelements (DGRs) that mutagenize the hankyphage minor tail fiber, and likely contribute to its broad host range. This study sheds light on the life cycle of this this abundant intestinal bacteriophage and highlights important gaps in our understanding of the factors required for the completion of its life cycle. Elucidating this puzzle will be critical to gain a better understanding of the hankyphage biology and ecological role.

microbiology↗

bioRxiv2023

Raynals, an online tool for the analysis of dynamic light scattering

Dynamic light scattering (DLS) is routinely employed to assess the homogeneity and size distribution profile of samples containing microscopic particles in suspension or solubilised polymers. In this work, we introduce Raynals, an user-friendly software for the analysis of single-angle DLS data that uses the Tikhonov-Phillips regularisation. Performance is evaluated on simulated and experimental data, generated by different DLS instruments, for several proteins and gold nanoparticles. DLS data can be easily misinterpreted and the simulation tools available in Raynals allow understanding of the limitations of the measurement and its resolution. It has been designed as a tool to address quality control of biological samples, during sample preparation and optimisation, and it helps in the detection of aggregates showing the influence of large particles. Last, Raynals provides flexibility in the way the data is presented, allows exporting publication-quality figures, it is free for academic use, and can be accessed online on the eSPC data analysis platform at spc.embl-hamburg.de.

biophysics↗

bioRxiv2023

Interactions of the Protein Tyrosine Phosphatase PTPN3 with Viral and Cellular Partners through its PDZ Domain: Insights into Structural Determinants and Phosphatase Activity

The human protein tyrosine phosphatase non-receptor type 3 (PTPN3) is a phosphatase containing a PDZ (PSD-95/Dlg/ZO-1) domain that has been found to play both tumor-suppressive and tumor-promoting roles in various cancers, despite limited knowledge of its cellular partners and signaling functions. Notably, the high-risk genital human papillomavirus (HPV) types 16 and 18 and the hepatitis B virus (HBV) target the PDZ domain of PTPN3 through PDZ-binding motifs (PBMs) in their E6 and HBc proteins respectively. This study focuses on the interactions between the PTPN3 PDZ domain (PTPN3-PDZ) and PBMs of viral and cellular protein partners. The solved X-ray structures of complexes between PTPN3-PDZ and PBMs of E6 of HPV18 and the tumor necrosis factor-alpha converting enzyme (TACE) reveal two novel interactions. We provide new insights into key structural determinants of PBM recognition by PTPN3 by screening the selectivity of PTPN3-PDZ recognition of PBMs, and by comparing the PDZome binding profiles of PTPN3-recognized PBMs and the interactome of PTPN3-PDZ. The PDZ domain of PTPN3 was known to auto-inhibit the proteins phosphatase activity. We discovered that the linker connecting the PDZ and phosphatase domains is involved in this inhibition, and that the binding of PBMs does not impact this catalytic regulation. Overall, the study sheds light on the interactions and structural determinants of PTPN3 with its cellular and viral partners, as well as on the inhibitory role of its PDZ domain on its phosphatase activity.

biophysics↗

bioRxiv2022

DNA-binding mechanism and evolution of Replication Protein A

Replication Protein A (RPA) is a heterotrimeric single stranded DNA-binding protein with essential roles in DNA replication, recombination and repair, in both eukaryotic and archaeal cells. By using an integrative approach that combines three crystal structures, four cryo-EM structures in complex with single-stranded DNA (ssDNA) of different lengths, we extensively characterized RPA from Pyrococcus abyssi in different states. These structures show two essential features conserved in eukaryotes: a trimeric core and a module that promotes cooperative binding to ssDNA, as well as a newly identified archaeal-specific domain. These structures reveal for the first time how ssDNA is handed over from one RPA complex to the other, and uncover an unanticipated mechanism of self-association on ssDNA tracts. This work constitutes a significant step forward in the molecular understanding of the structure and DNA-binding mechanism of RPA, with far-reaching implications for the evolution of this primordial replication factor in Archaea and Eukarya.

biochemistry↗

bioRxiv2021

Acetylation regulates the oligomerization state and activity of RNase J, the major ribonuclease of Helicobacter pylori

In Helicobacter pylori, post-transcriptional regulation strongly relies on the activity of an RNA degradosome, composed of the essential ribonuclease RNase J and the DEAD-box RNA helicase RhpA. Here, we describe post-translational modifications of this protein complex that affect its activity. Cell-extracted RNase J is acetylated on multiple residues, one of which, K649, strongly impacts RNase J oligomerization, which in turn influences ribonuclease activity. Corroborating the link between oligomerization and activity, mutations targeting K649 and other residues affect the dimerization and in vitro activity of RNase J. Our crystal structure of RNase J reveals three loops that gate access to the active site and rationalizes how oligomerization state influences activity. The acetylated residues of RNase J are important for H. pylori morphology, highlighting that the modifications affect the RNase J cellular function. We propose acetylation as a regulatory level controlling the activity of RNase J and the H. pylori RNA degradosome.

microbiology↗

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

A high-affinity calmodulin-binding site in the CyaA toxin translocation domain is essential for invasion into eukaryotic cells

The molecular mechanisms and forces involved in the translocation of bacterial toxins into host cells have thus far remained elusive. The adenylate cyclase (CyaA) toxin from Bordetella pertussis displays a unique intoxication pathway in which its catalytic domain is directly translocated across target cell membranes. We have previously identified a translocation region in CyaA that contains a segment, P454 (residues 454-484), exhibiting membrane-active properties related to antimicrobial peptides. Herein, we show that this peptide is able to translocate across membranes and interact with calmodulin. Structural and biophysical analyses have revealed the key residues of P454 involved in membrane destabilization and calmodulin binding. Mutational analysis demonstrated that these residues play a crucial role in CyaA translocation into target cells. We have also shown that calmidazolium, a calmodulin inhibitor, efficiently blocks CyaA internalization. We propose that after CyaA binding to target cells, the P454 segment destabilizes the plasma membrane, translocates across the lipid bilayer and binds calmodulin. Trapping of the CyaA polypeptide chain by the CaM:P454 interaction in the cytosol may assist the entry of the N-terminal catalytic domain by converting the stochastic process of protein translocation into an efficient vectorial chain transfer into host cells.

biophysics↗

bioRxiv2020

Actinobacteria challenge the paradigm: a unique protein architecture for a well-known central metabolic complex

-ketoacid dehydrogenase complexes are large, tripartite enzymatic machineries carrying out key reactions in central metabolism. Extremely conserved across the tree of life, they have so far all considered to be structured around a high molecular weight hollow core, consisting of up to 60 subunits of the acyltransferase component. We provide here evidence that Actinobacteria break the rule by possessing an acetyltranferase component reduced to its minimally active, trimeric unit, characterized by a unique C-terminal helix that affects the oligomerization and the full 3D architecture of the complex. We show that this unique feature is characterized by an insertion, which together with OdhA is found spread over Actinobacteria. This phylum includes organisms or great interest for agriculture, industrial bio-production and many human pathogens as Mycobacterium tuberculosis. Moreover, components of this complex are key for M. tuberculosis survival in the human host, and its unique core and protein-protein interactions represent potentially "druggable" targets.

microbiology↗