Biology subjects

Maric, H. M.

Publications and source records attributed to Maric, H. M..

10 recordsLinked to original sources

bioRxiv2025

Cryo-EM Structures of Higher Order Gephyrin OligomersReveal Principles of Inhibitory Postsynaptic Scaffold Organization

Gephyrin is the principal scaffolding protein of inhibitory postsynaptic densities, clustering glycine and GABAA receptors via multivalent interactions. It features structured N and C terminal domains connected by an intrinsically disordered linker. Although the structural and functional properties of its terminal domains are well characterized, the mechanism by which full-length gephyrin organizes into higher-order complexes remains unresolved. Here, we combine biochemical reconstitution, cryo-electron microscopy, and mutational analyses to elucidate the structural logic of gephyrin oligomerization. We demonstrate that gephyrin adopts a stable dimeric assembly which constitutes the basic unit for both linear and oblique tetramers as well as linear hexameric arrangements. High resolution structures reveal a critical segment of the flexible linker that adopts two distinct conformations, one of which occludes the receptor-binding site. This segment harbors key phosphorylation sites, providing a mechanistic link between structural conformation and regulatory control. Our findings redefine the architecture of inhibitory synapses and reconcile gephyrin oligomerization models with published in-situ post-synaptic densities characterized by cryo-electron tomography.

neuroscience↗

bioRxiv2025

Distinct myeloid precursors and their interaction with mesenchymal cells orchestrate the spreading of psoriatic disease from the skin to the joints

Psoriatic disease initially affects the skin, but later extends to the joints. Herein, we describe a two-step process that orchestrates spreading of inflammation from the skin to the joints. Induction of psoriatic skin disease in photoconvertible mice, followed by sequencing and computational characterization of skin-derived cells in the joints, identified a unique population of CD2+ MHC-II+ CCR2+ myeloid precursors that built up a skin-derived myeloid cell compartment in the joints. Single-cell cross-species reference mapping and mitochondrial variant tracing showed an orthologue human cell population. Interactome analyses in the joints showed that in a second step, resident regulatory CD200+ fibroblasts critically regulate the priming of the CD2+ MHC-II+ CCR2+ myeloid precursors, which subsequently regulate the IL-17 expression in T cells. Hence, spreading of inflammation requires a distinct migratory myeloid precursor population and a permissive local tissue environment, similar to tumour metastasis. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=121 SRC="FIGDIR/small/665302v1_ufig1.gif" ALT="Figure 1"> View larger version (24K): org.highwire.dtl.DTLVardef@38c440org.highwire.dtl.DTLVardef@dc574dorg.highwire.dtl.DTLVardef@1e79f72org.highwire.dtl.DTLVardef@19508cf_HPS_FORMAT_FIGEXP M_FIG C_FIG

immunology↗

bioRxiv2025

Nanobinders for Synaptotagmin 1 enable the analysis of synapticvesicle dynamics in rodent and human models.

Synaptic neurotransmission is a critical hallmark of brain activity and one of the first processes to be affected in neural diseases. Monitoring this process, and in particular synaptic vesicle recycling, in living cells has been instrumental in unraveling mechanisms responsible for neurotransmitter release. However, currently available reporters suffer from major limitations such large probe size or lack of suitability for human neurons, hampering the understanding of human synaptic pathophysiology. Here we describe the NbLumSyt1 toolkit, a panel of nanobody-based affinity probes targeting the luminal domain of the synaptic vesicle protein Synaptotagmin 1 (Syt1). These new tools enable quantitative, non-invasive imaging and functional interrogation of synaptic transmission in human neurons, with unprecedented precision, versatility and cost efficiency, in technologies ranging from fixed-and live-cell super-resolution imaging to electron microscopy and mass spectrometry. Overall, NbLumSyt1 nanobinders provide a valuable platform for human synaptic physiology and pathophysiology, benefiting fundamental neuroscience and translational efforts to study and develop treatments for brain-related disorders.

neuroscience↗

bioRxiv2025

Epitope Sequence and Modification Fingerprints of Anti-Aβ Antibodies

A hallmark of Alzheimers disease (AD), the most common form of dementia, is the progressive accumulation of amyloid-beta (A{beta}) peptides across distinct brain regions. Anti-A{beta} antibodies (A{beta}-Abs) targeting specific A{beta} variants are essential tools for AD research, diagnostics, and therapy. The monoclonal antibodies Aducanumab, Lecanemab, and Donanemab have recently been approved as the first disease-modifying treatments for early AD, highlighting the clinical importance of their exact binding profiles. In this study, we systematically characterized the binding and modification requirements of 20 A{beta}-Abs, including biosimilars of Aducanumab, Lecanemab, and Donanemab, across monomeric, oligomeric, and aggregated A{beta} forms. Array-based analysis of 20,000 modified A{beta} peptides defined binding epitopes at single-residue resolution and revealed the impact of sequence variation, including familial AD mutations, as well as diverse post-translational modifications (PTMs). Notably, genetic variants such as H6R impaired binding of therapeutic A{beta}-Abs like Aducanumab. Donanemab showed strong preference for pyroglutamate-modified A{beta}pE3-10, while Lecanemab and Aducanumab exhibited aggregation- and sequence-context-dependent binding requirements. Comparison of peptide binding profiles with binding of full-length and aggregated A{beta} via immunoprecipitation-mass spectrometry, capillary immunoassays, Western blotting, and immunohistochemistry on AD brain tissue revealed distinct aggregation-dependent binding behaviours. The valency- and context-dependence of Aducanumab binding, together with its preference for Ser8-phosphorylated A{beta}, supports a dimerization-mediated binding mechanism. For Lecanemab, our data suggest that additional structural contributions beyond the minimal N-terminal epitope are required for binding to aggregated A{beta}, which remain to be fully resolved. Together, this work provides the most comprehensive dataset to date on aggregation-dependent sequence and modification selectivity of A{beta}-Abs. By integrating mutational, PTM, and aggregation contexts in a unified experimental framework, we establish a resource that enables rational selection of antibodies for research and diagnostic applications, and offers mechanistic insights that may inform the design and optimization of future therapeutic antibodies in AD.

biochemistry↗

bioRxiv2024

Competition between glycine and GABAA receptors for gephyrin controls their equilibrium populations at inhibitory synapses

Glycine and GABA receptors are ligand-gated chloride channels that mediate inhibitory neurotransmission throughout the central nervous system. The receptors co-localise widely at inhibitory synapses in the spinal cord and in the brainstem due to their interaction with an overlapping binding site of the synaptic scaffold protein gephyrin, pointing to a direct competition between the different receptor types. We have put this hypothesis to the test using single molecule approaches to measure receptor-gephyrin interactions in cells and in vitro. We explored the effects of receptor competition at inhibitory synapses in living neurons by measuring the change in the accumulation and effective stabilisation energy of glycine receptors in the presence of interfering GABA receptor complexes through single molecule tracking and diffusion analysis. Secondly, using molecular tweezers, we quantified the thermodynamic properties of receptor-gephyrin binding, demonstrating direct and reversible competition through the addition of interacting peptides in solution. The relatively low affinity of GABA receptor subunits for gephyrin compared to the glycine receptor raises interesting questions about the role of this competition in synaptic plasticity. We hypothesize that GABA and glycine receptor competition constitutes a molecular system designed to reconcile synapse stability and plasticity at mixed inhibitory synapses.

neuroscience↗

bioRxiv2024

RNA-mediated MYC multimerization suppresses innate immune signaling

In response to perturbed transcription elongation, the MYC oncoprotein multimerizes and undergoes a phase transition; the underlying mechanisms and their function are unknown. Here, we show that MYC re-localizes from its canonical location on DNA to RNA in response to the accumulation of intronic RNA. MYC binds RNA directly, which enhances its multimerization. MYC multimers concentrate the nuclear exosome, a 3-5 RNA exonuclease, and its targeting complexes around double-stranded RNA and R-loops, and promote exosome recruitment to R-loops. RNA binding of MYC suppresses activation of the innate immune kinase TBK1. Upon MYC depletion, intron-derived dsRNAs, including RNA derived from repetitive elements and small nucleolar RNAs, accumulate on TLR3, a pattern recognition receptor that activates TBK1. In MYC-depleted cells, TLR3-bound snoRNAs carry aberrant 3-ends, indicating defective exosomal processing. Our data show that the phase transition of MYC is a RNA-driven stress response that suppresses the accumulation of immunogenic RNAs.

molecular biology↗

bioRxiv2024

Induction of Hepatitis B Core Protein Aggregation Targeting an Unconventional Binding Site

The hepatitis B virus (HBV) infection is a major global health problem, with chronic infection leading to liver complications and high death toll. Current treatments, such as nucleos(t)ide analogs and interferon-, effectively suppress viral replication but rarely cure the infection. To address this, new antivirals targeting different components of the HBV molecular machinery are being developed. Here we investigated the hepatitis B core protein (HBc) that forms the viral capsids and plays a vital role in the HBV life cycle. We explored two distinct binding pockets on the HBV capsid: the central hydrophobic pocket of HBc-dimers and the pocket at the tips of capsid spikes. We synthesized a geranyl dimer that binds to the central pocket with micromolar affinity, and dimeric peptides that bind the spike-tip pocket with sub-micromolar affinity. Cryo-electron microscopy further confirmed the binding of peptide dimers to the capsid spike tips and their capsid-aggregating properties. Finally, we show that the peptide dimers induce HBc aggregation in vitro and in living cells. Our findings highlight two tractable sites within the HBV capsid and provide an alternative strategy to affect HBV capsids.

microbiology↗

bioRxiv2023

Direct RNA-binding by MYCN mediates feedback from RNA processing to transcription control

The MYCN oncoprotein broadly binds active promoters in a heterodimer with its partner protein MAX. MYCN also interacts with the nuclear exosome, a 3-5 exoribonuclease complex, suggesting a function in RNA metabolism. Here we show that MYCN forms stable high molecular weight complexes with the exosome and multiple RNA-binding proteins. In cells, MYCN binds to thousands of intronic RNAs; recombinant MYCN directly binds RNA via a short, highly conserved sequence termed MYCBoxI. Perturbing exosome function results in global re-localization of MYCN from promoters to intronic RNAs. At promoters, MYCN is then replaced by the MNT(MXD6) repressor protein, which inhibits MYCN-dependent transcription. MYCN promotes the degradation of its bound introns via the nuclear exosome targeting (NEXT) complex. Our data demonstrate that MYCN is an RNA-binding protein that regulates nascent transcript turnover and show that competition between its RNA- and DNA-bound states links the dynamics of the MYCN/MAX/MXD network to mRNA processing.

cancer biology↗

bioRxiv2022

A bead-based GPCR phosphorylation immunoassay for high-throughput ligand profiling and GRK inhibitor screening

Analysis of agonist-driven phosphorylation of G protein-coupled receptors (GPCRs) can provide valuable insights into the receptor activation state and ligand pharmacology. However, to date, assessment of GPCR phosphorylation using high-throughput applications has been challenging. We have developed and validated a bead-based immunoassay for the quantitative assessment of agonist-induced GPCR phosphorylation that can be performed entirely in multiwell cell culture plates. The assay involves immunoprecipitation of affinity-tagged receptors using magnetic beads followed by protein detection using phosphorylation-state-specific and phosphorylation state-independent anti-GPCR antibodies. As proof of concept, five prototypical GPCRs (MOP, C5a1, D1, SST2, CB2) were treated with different agonists and antagonists, and concentration-response curves were generated. We then extended our approach to establish selective cellular GPCR kinase (GRK) inhibitor assays, which led to the rapid identification of a selective GRK5/6 inhibitor (LDC8988) and a highly potent pan-GRK inhibitor (LDC9728). In conclusion, this versatile GPCR phosphorylation assay can be used extensively for ligand profiling and inhibitor screening.

pharmacology and toxicology↗

bioRxiv2021

Sylites: Multipurpose markers for the visualization of inhibitory synapses

We introduce Sylites - small and versatile fluorogenic affinity probes for high-contrast visualization of inhibitory synapses. Having stoichiometric labeling and exceptional selectivity for neuronal gephyrin, a hallmark protein of the inhibitory post-synapse, Sylites enable superior synapse staining compared with antibodies. Combined with super-resolution microscopy, Sylites allow precise nanoscopic measurements of the synapse. In brain tissue, Sylites reveal the three-dimensional distribution of inhibitory synapses within just an hour.

neuroscience↗