Biology subjects

Lyons, S. P.

Publications and source records attributed to Lyons, S. P..

6 recordsLinked to original sources

bioRxiv2026

No evidence for direct physical interaction of 5-HT2A-mGluR2 receptors in vitro or in vivo

Activation of mGluR2 (metabotropic glutamate receptor 2), the primary presynaptic autoreceptor for glutamate in the brain, is well established to attenuate the psychedelics-mediated behavioral and electrophysiological effects. However, the mechanisms responsible for these actions are controversial. The two competing mechanistic hypotheses have been proposed to explain this phenomenon are: (1) direct actions mediated by mGluR2/5-HT2A heterodimers, and (2) inhibition of 5-HT2A-mediated excitation of pyramidal neurons via presynaptic inhibition of glutamate release by mGluR2 receptors. Consistent with prior reports, we show that mGluR2 agonist pretreatment attenuates the head twitch response induced by the psychedelic drug 1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane (DOI) in mice engineered to express mGluR2-mCherry and 5-HT2A-eGFP-CT tagged receptors. We next employed multiple orthogonal in vivo and in vitro approaches to explore the potential for direct physical interactions between mGluR2 and 5-HT2A receptors. Across all approaches, we found no evidence for receptor colocalization or oligomerization under basal or 5-HT2A agonist-exposed conditions in vitro or in vivo. Radioligand binding and kinetic analyses revealed no evidence for mGluR2-mediated modulation of 5-HT2A ligand binding in vitro or in vivo. Collectively, our findings support models in which mGluR2 signaling modulates the activity of Gq-coupled 5-HT2A receptors in layer V pyramidal neurons, rather than models positing the requirement of mGluR2/5-HT2A multimers.

neuroscience↗

bioRxiv2026

APOE interacts with COX-2 on lipid droplets to modulate inflammatory lipid signaling

Alzheimers Disease (AD) is the leading cause of dementia worldwide. Expression of the E4 variant of apolipoprotein E (APOE) greatly increases individuals risk of developing AD. In response to lipogenesis in astrocytes, APOE can escape secretion and traffic to the cytoplasmic surface of lipid droplets (LDs), but protein interactors of APOE at the LD were unknown. Here we find that LD-localized APOE physically interacts with the inflammatory lipid signaling enzyme cyclooxygenase-2 (COX-2). Like APOE, COX-2 can avoid the secretory pathway and traffic to LDs in response to lipogenesis. APOE3, but not APOE4, increases COX-2 localization to LDs. Computational modeling, microscopy-based assays, and targeted lipidomics reveal that APOE3 promotes while APOE4 suppresses COX-2 enzymatic activity at LDs and intracellular prostaglandin production. This work identifies a novel and targetable protein-protein interaction of APOE and provides a mechanistic link between APOE4 and dysregulated inflammatory lipid signaling.

cell biology↗

bioRxiv2026

Cryo-EM Structures of Brain-Derived G Protein-Coupled Receptors: The First Direct Visualization from Mammalian Brain Tissue

Glutamate is the main excitatory neurotransmitter in the brain and mediates its actions by both ionotropic (e.g. NMDA and AMPA) and metabotropic glutamate receptors (mGluRs). The Groups II and III mGluRs, which pre-synaptically inhibit glutamate release, are important for synaptic plasticity, modulating neuronal excitation, learning and memory. Our current understanding of the structural organization and dynamics of these and other mGluRs, as well as most other GPCRs, relies mainly on studies using recombinant and highly engineered systems in vitro. Here, we combine CRISPR-mediated protein tagging, proteomics and a rapid immunoaffinity purification method to isolate endogenous mGluR2-containing assemblies from mouse brain and visualize them via cryo-EM. Analysis of the particle sets reveals the molecular structures of at least 11 distinct endogenous receptor assemblies that span active and inactive states, homomeric and heteromeric dimers, and G protein-coupled and uncoupled species. We find that mGluR2 homodimers and mGluR2/3 heterodimers are the major endogenous mGluR2-containing species present in the brain, with the mGluR2/3 heterodimers detected only in active state complexes, potentially reflecting basal activation of mGluR3 containing dimers by chloride. Reconstructing a comprehensive conformational equilibrium for the brain-isolated receptors in detergent reveals endogenous ternary complexes comprising mGluR2 homodimers and mGluR2/3 heterodimers with a single GoA heterotrimer which exhibit significant differences from prior studies with recombinant systems. Our work illuminates the endogenous conformational, proteomic and compositional landscape of the heterogenous mGluR2 complexes in the brain, thereby providing a structural framework for the pathophysiology of psychiatric disorders. This information has the potential to be leveraged for therapeutic targeting of endogenous glutamatergic signaling complexes.

neuroscience↗

bioRxiv2025

Non-redundant roles for paralogous proteins in the yeast glucose-sensing pathway

Paralogs engage in biological processes through both redundant and non-redundant functions. In the yeast Saccharomyces cerevisiae, approximately one-fifth of the genome consists of paralogs, with their encoded proteins involved in multiple pathways. However, the unique contributions of individual paralogs have remained poorly defined. Here, we undertook a systematic examination of eight paralog pairs in the glucose-sensing pathways, deleting each component and measuring the resulting changes in gene expression. To that end we established a new transcription reporter system to monitor the response to glucose as well as to non-preferred sugars in single cells. Focusing on the PKA catalytic subunits, comprised of the paralogs Tpk1 and Tpk3 as well as the isomorphic kinase Tpk2, we employed mass spectrometry to identify their contribution to cellular metabolism, used a GFP-based sensor to follow changes in cytosolic pH, and used BioID to identify unique and shared binding partners. Our data reveal that paralogs in the glucose-sensing pathway contribute in multiple and unique ways to signal transduction, and establish potential mechanisms driving the preservation of these and other duplicated genes throughout long periods of evolution.

genetics↗

bioRxiv2025

Chemoproteomic Profiling of C. albicans for Characterization of Anti-fungal Kinase Inhibitors

Candida albicans is a growing health concern as the leading causal agent of systemic candidiasis, a life-threatening fungal infection with a mortality rate of [~]40% despite best available therapy. Yck2, a fungal casein kinase 1 (CK1) family member, is the cellular target of inhibitors YK-I-02 (YK) and MN-I-157 (MN). Here, multiplexed inhibitor beads paired with mass spectrometry (MIB/MS) employing ATP-competitive kinase inhibitors were used to define the selectivity of these Yck2 inhibitors across the global C. albicans proteome. The MIB matrix captured 89% of the known and predicted C. albicans protein kinases present in cell lysate. In MIB/MS competition assays, YK and MN demonstrated exquisite selectivity across the C. albicans fungal kinome with target engagement of only three CK1 homologs (Yck2, Yck22, and Hrr25) and a homolog of human p38 (Hog1). Additional chemoproteomics using a custom MN-kinobead identified only one additional C. albicans protein, confirming its remarkable fungal proteome-wide selectivity. To identify new Yck2 inhibitors with selectivity over Hog1, thirteen human CK1 kinase inhibitors were profiled for fungal kinase-binding activity using MIB/MS competition assays and in-cell NanoBRET target engagement assays. A new chemotype of family-selective Yck2 inhibitors with antifungal activity was identified. Together, these findings expand the application of MIB/MS proteomic profiling for non-human kinomes and demonstrate its utility in the discovery and development of selective inhibitors of fungal kinases with potential antimicrobial activity. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=81 SRC="FIGDIR/small/632200v1_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@1606f86org.highwire.dtl.DTLVardef@39c92borg.highwire.dtl.DTLVardef@1c666cborg.highwire.dtl.DTLVardef@869b5c_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2021

Regulation of PP2A, PP4, and PP6 holoenzyme assembly by carboxyl-terminal methylation

The family of Phosphoprotein Phosphatases (PPPs) is responsible for most cellular serine and threonine dephosphorylation. PPPs achieve substrate specificity and selectivity by forming multimeric holoenzymes. PPP holoenzyme assembly is tightly controlled, and changes in the cellular repertoire of PPPs are linked to human disease, including cancer and neurodegeneration. For PP2A, PP4, and PP6, holoenzyme formation is in part regulated by carboxyl (C)-terminal methyl-esterification (often referred to as "methylation"). Here, we use mass spectrometry-based proteomics, methylation-ablating mutations, and genome editing to elucidate the role of C-terminal methylation on PP2A, PP4, and PP6 holoenzyme assembly. We find that the catalytic subunits of PP2A, PP4, and PP6 are frequently methylated in cancer cells and that deletion of the C-terminal leucine faithfully recapitulates loss of methylation. We observe that loss of PP2A methylation consistently reduced B55, B56, and B72 regulatory subunit binding in cancer and non-transformed cell lines. However, Striatin subunit binding is only affected in non-transformed cells. For PP4, we find that PP4R1 and PP4R3{beta} bind in a methylation-dependent manner. Intriguingly, loss of methylation does not affect PP6 holoenzymes. Our analyses demonstrate in an unbiased, comprehensive, and isoform-specific manner the crucial regulatory function of endogenous PPP methylation in transformed and non-transformed cell lines

biochemistry↗