A key issue in neuronal circuit regulation is how synapse formation is initiated. Synapse formation could start when one or more synaptic scaffold proteins that can initiate synapse formation reach certain threshold concentrations in the dendritic shaft, which might lead to their oligomerization or even liquid-liquid phase separation (LLPS). By combining in vitro reconstitution of purified proteins with live-cell single-molecule and confocal imaging, we demonstrated that SynGAP alone forms assemblies of nanoscale clusters containing several to several tens of molecules at 10-nM order concentrations and micron-scale LLPS hydrogel-like condensates at submicromolar concentrations. The trimers of SynGAP’s intrinsically disordered region (IDR) induced by its coiled-coil domain are responsible for SynGAP condensation. CaMKII-mediated phosphorylation moderately suppresses SynGAP condensation, and also increases condensate liquidity. While PSD95 fails to form assemblies under these conditions, it is recruited to SynGAP condensates by specifically binding to the PDZ-binding motif of SynGAP. SynGAP[PSD95] condensates selectively immobilize postsynaptic transmembrane proteins, Neuroligin1 and AMPAR-TARP2 complexes, in a manner dependent on their oligomerization state, indicating cooperative recruitment dynamics among SynGAP, PSD95, and transmembrane components, which might mimic initial PSD assembly. These findings suggest that SynGAP may act as a primary nucleator of postsynaptic density assembly, challenging the PSD95-centered models.
", "doi": "10.1101/2025.04.22.649955", "publisher": "bioRxiv", "publication_date": "2025-04-23" }, { "id": "authors:6e0sn-ana02", "collection": "authors", "collection_id": "6e0sn-ana02", "cite_using_url": "https://authors.library.caltech.edu/records/6e0sn-ana02", "type": "monograph", "title": "A spatial model of autophosphorylation of Ca\u00b2\u207a/calmodulin-dependent protein kinase II in a glutamatergic spine reveals dynamics of kinase activation in the first several seconds after a complex synaptic stimulus", "author": [ { "family_name": "Bartol", "given_name": "Thomas M.", "orcid": "0009-0002-2598-0052", "clpid": "Bartol-Thomas-M" }, { "family_name": "Ordyan", "given_name": "Mariam", "orcid": "0000-0003-0064-2997", "clpid": "Ordyan-Mariam" }, { "family_name": "Sejnowski", "given_name": "Terrence J.", "clpid": "Sejnowski-Terrence-J" }, { "family_name": "Rangamani", "given_name": "Padmini", "clpid": "Rangamani-Padmini" }, { "family_name": "Kennedy", "given_name": "Mary B.", "orcid": "0000-0003-1369-0525", "clpid": "Kennedy-M-B" } ], "abstract": "Activation of N-methyl-D-aspartate-type glutamate receptors (NMDARs) at synapses in the CNS triggers changes in synaptic strength that underlie memory formation in response to strong synaptic stimuli. The primary target of Ca2+ flowing through NMDARs is Ca2+/calmodulin-dependent protein kinase II (CaMKII) which forms dodecameric holoenzymes that are highly concentrated at the postsynaptic site. Activation of CaMKII is necessary to trigger long-term potentiation of synaptic strength (LTP), and is prolonged by autophosphorylation of subunits within the holoenzyme. Here we use MCell4, an agent-based, stochastic, modeling platform to model CaMKII holoenzymes placed within a realistic spine geometry. We show how two mechanisms of regulation of CaMKII, ‘Ca2+-calmodulin-trapping (CaM-trapping)’ and dephosphorylation by protein phosphatase-1 (PP1) shape the autophosphorylation response during a repeated high-frequency stimulus. Our simulation results suggest that autophosphorylation of CaMKII does not constitute a bistable switch. Instead, prolonged but temporary, autophosphorylation of CaMKII may contribute to a biochemical-network-based ‘kinetic proof-reading” mechanism that controls induction of synaptic plasticity.
", "doi": "10.1101/2024.02.02.578696", "publisher": "BioRxiv", "publication_date": "2024-07-18" }, { "id": "authors:wgjvx-w0g19", "collection": "authors", "collection_id": "wgjvx-w0g19", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210419-173243907", "type": "monograph", "title": "Sonicated fibrils of huntingtin exon-1 preferentially seed neurons and produce toxic assemblies", "author": [ { "family_name": "Chongtham", "given_name": "Anjalika", "orcid": "0000-0001-8437-3899", "clpid": "Chongtham-Anjalika" }, { "family_name": "Isas", "given_name": "J. Mario", "clpid": "Isas-J-Mario" }, { "family_name": "Pandey", "given_name": "Nitin K.", "orcid": "0000-0001-6124-4090", "clpid": "Pandey-Nitin-K" }, { "family_name": "Rawat", "given_name": "Anoop", "orcid": "0000-0002-5838-0275", "clpid": "Rawat-Anoop" }, { "family_name": "Yoo", "given_name": "Jung Hyun", "orcid": "0000-0002-5159-8167", "clpid": "Yoo-Jung-Hyun" }, { "family_name": "Mastro", "given_name": "Tara", "clpid": "Mastro-Tara-L" }, { "family_name": "Kennedy", "given_name": "Mary", "orcid": "0000-0003-1369-0525", "clpid": "Kennedy-M-B" }, { "family_name": "Langen", "given_name": "Ralf", "orcid": "0000-0003-2816-6531", "clpid": "Langen-Ralf" }, { "family_name": "Khoshnan", "given_name": "Ali", "orcid": "0000-0002-0070-9808", "clpid": "Khoshnan-Ali" } ], "abstract": "HD is a genetically inherited neurodegenerative disorder caused by expansion of a polyglutamine (polyQ) repeats in the exon-1 of huntingtin protein (HTT). The expanded polyQ enhances the amyloidogenic propensity of HTT exon 1 (HTTex1), which forms a heterogeneous mixture of assemblies with some being neurotoxic. While predominantly intracellular, monomeric and aggregated mutant HTT species are also present in the cerebrospinal fluids of HD patients, however, their biological properties are not well understood. To explore the role of extracellular mutant HTT in aggregation and toxicity, we investigated the possible uptake and amplification of recombinant HTTex1 assemblies in cell culture models. We found seedingcompetent species in the sonicated HTTex1 fibrils, which preferentially entered human neurons and triggered the amplification of neurotoxic assemblies; astrocytes or epithelial cells were not permissive to the HTTex1 seeding. The aggregation of HTTex1 seeds in neurons depleted endogenous HTT protein with non-pathogenic polyQ repeat, activated apoptotic caspase-3 pathway and induced nuclear fragmentation. Using a panel of novel monoclonal antibodies and genetic mutation, we identified epitopes within the N-terminal 17 amino acids and proline-rich domain of HTTex1 mediating neural seeding. Synaptosome preparations from the brains of HD mice also contained similar neurotoxic seeding-competent mutant HTT species. Our findings suggest that amyloidogenic extracellular mutant HTT assemblies may selectively enter neurons, propagate and produce neurotoxic assemblies.", "doi": "10.1101/2021.04.16.440200", "publication_date": "2021-04-19" }, { "id": "authors:f31jk-vnw59", "collection": "authors", "collection_id": "f31jk-vnw59", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20191014-134400805", "type": "monograph", "title": "A sex difference in the composition of the rodent postsynaptic density", "author": [ { "family_name": "Mastro", "given_name": "Tara L.", "clpid": "Mastro-T-L" }, { "family_name": "Preza", "given_name": "Anthony", "clpid": "Preza-A" }, { "family_name": "Basu", "given_name": "Shinjini", "clpid": "Basu-Shinjini" }, { "family_name": "Chattarji", "given_name": "Shona", "orcid": "0000-0001-9962-3635", "clpid": "Chattarji-S" }, { "family_name": "Till", "given_name": "Sally M.", "clpid": "Till-S-M" }, { "family_name": "Kind", "given_name": "Peter", "orcid": "0000-0002-4256-9639", "clpid": "Kind-P" }, { "family_name": "Kennedy", "given_name": "Mary B.", "orcid": "0000-0003-1369-0525", "clpid": "Kennedy-M-B" } ], "abstract": "SynGAP is a postsynaptic density (PSD) protein that binds to PDZ domains of the scaffold protein PSD-95. We previously reported that heterozygous deletion of synGAP in mice is correlated with increased steady-state levels of other key PSD proteins that bind PSD-95, although the level of PSD-95 remains constant (Walkup et al., 2016). For example, the ratio to PSD-95 of Transmembrane AMPA-Receptor-associated Proteins (TARPs), which mediate binding of AMPA-type glutamate receptors to PSD-95, was increased in young synGAP+/- mice. Here we show that a highly significant increase in TARP in the PSDs of young synGAP+/- rodents is present only in females and not in males. The data reveal a sex difference in the adaptation of the PSD scaffold to synGAP heterozygosity.", "doi": "10.1101/802538", "publication_date": "2019-10-12" }, { "id": "authors:4v36z-r4204", "collection": "authors", "collection_id": "4v36z-r4204", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160718-135600220", "type": "monograph", "title": "Binding of synGAP to PDZ Domains of PSD-95 is Regulated by Phosphorylation and Shapes the Composition of the Postsynaptic Density", "author": [ { "family_name": "Walkup", "given_name": "Ward G.", "orcid": "0000-0002-0385-6256", "clpid": "Walkup-W-G-IV" }, { "family_name": "Mastro", "given_name": "Tara", "clpid": "Mastro-T-L" }, { "family_name": "Schenker", "given_name": "Leslie T.", "clpid": "Schenker-L-T" }, { "family_name": "Vielmetter", "given_name": "Jost", "clpid": "Vielmetter-J" }, { "family_name": "Hu", "given_name": "Rebecca", "clpid": "Hu-Rebecca" }, { "family_name": "Iancu", "given_name": "Ariella", "clpid": "Iancu-A" }, { "family_name": "Reghunathan", "given_name": "Meera", "clpid": "Reghunathan-M" }, { "family_name": "Bannon", "given_name": "B. Dylan", "clpid": "Bannon-B-D" }, { "family_name": "Kennedy", "given_name": "Mary B.", "orcid": "0000-0003-1369-0525", "clpid": "Kennedy-M-B" } ], "abstract": "SynGAP is a Ras/Rap GTPase-activating protein (GAP) present in high concentration in postsynaptic densities (PSDs) from mammalian forebrain where it binds to all three PDZ (PSD-95, Discs-large, ZO-1) domains of PSD-95. We show that phosphorylation of synGAP by Ca^(2+)/calmodulin-dependent protein kinase II (CaMKII) decreases its affinity for the PDZ domains as much as 10-fold, measured by surface plasmon resonance. SynGAP is abundant enough in postsynaptic densities (PSDs) to occupy about one third of the PDZ domains of PSD-95. Therefore, we hypothesize that phosphorylation by CaMKII reduces synGAP\u2032s ability to restrict binding of other proteins to the PDZ domains of PSD-95. We support this hypothesis by showing that three critical postsynaptic signaling proteins that bind to the PDZ domains of PSD-95 are present at a higher ratio to PSD-95 in PSDs isolated from synGAP heterozygous mice.", "doi": "10.1101/058016", "publication_date": "2016-06-09" } ]