| Annotated protein: | Synaptic Ras GTPase activating protein 1 homolog (rat). Gene symbol: SYNGAP1. Taxonomy: Mus musculus (Mouse). Uniprot ID: J3QQ18 |
| antibody wiki: | |
| SynGO gene info: | SynGO data @ SYNGAP1 |
| Ontology domain: | Biological Process |
| SynGO term: | modulation of chemical synaptic transmission (GO:0050804) |
| Synapse type(s): | hippocampus, glutamatergic |
| Annotated paper: | Zeng M, et al. "Phase Transition in Postsynaptic Densities Underlies Formation of Synaptic Complexes and Synaptic Plasticity" Cell. 2016 Aug 25;166(5):1163-1175.e12 PMID:27565345 |
| Figure(s): | Figure 4A-D, F, G; Figure 7 |
| Annotation description: | Figure 4A-D, F, G. SynGAP/PSD-95 complex form liquid phase transition aggregation in vitro Literal: "During the sample preparations for light-scattering experiments, we found that mixing purified SynGAP CC-PBM and PSD-95 PSG above certain concentrations caused the sample solutions to become opalescent immediately. In contrast, solutions containing each individual component were always clear. We examined the solution of the SynGAP CC-PBMand PSD-95 PSG mixture shortly after mixing by light microscope and observed numerous small spherical droplets spanning various diameters, a phenomenon characteristic of liquid-to-liquid phase separation (Figure 4A). Within minutes, small droplets gradually coalesced into larger ones (Figure 4B). Isolated solutions of SynGAP CC-PBM and PSD-95 PSG, our controls, remained clear aqueous solutions at the same concentration (Figure 4A). To analyze the molecular compositions of the condensed liquid phase, we performed a sedimentation assay to separate the condensed liquid phase from the bulk aqueous solutions by centrifugation and assessed protein components in each fraction by SDS-PAGE with Coomassie blue staining (Figures 4C and 4D). Neither SynGAP CC-PBM nor PSD-95 PSG alone could form condensed liquid phase (Figure 4D). For the 1:1 molar ratio mixture of SynGAP CC-PBM and PSD-95 PSG at 100 mM, approximately half of SynGAP and PSD-95 were recovered from the condensed liquid phase (Figure 4D), indicating that it contains both SynGAP CCPBM and PSD-95 PSG. Considering that the condensed liquid phase droplet pellet volume is much smaller than that of the supernatant aqueous solution, protein concentrations for both SynGAP and PSD-95 in the condensed liquid phase are much higher (estimated to be at least 100-fold higher based on the volumes of the two fractions) than those in the aqueous solution." "The addition of a 15-residue SynGAP peptide, which binds to PSD-95 PDZ3-C with the same affinity as the SynGAP PBM does (Figure 1C), led to immediate dispersion of the condensed liquid phase into homogenous aqueous solution (Figure 4F; Movie S1) in a peptide concentration-dependent manner (Figure 4G)." Figure 7. SynGAP trimer formation and PSD-95 Binding regulates synaptic plasticity Literal: "Next, we examined if these SynGAP mutations might affect synaptic plasticity. We replaced endogenous SynGAP with the 'L-D&K-D' mutant or PSD-95 PDZ binding mutants, and also co-transfected mCherry as a cell morphology tracer and SEPGluA1 for monitoring AMPAR trafficking (Figures 7A and 7B). As to WT-SynGAP, following chemLTP induction, some synaptic spines were structurally enlarged, with newly inserted AMPARs (marked with arrows in yellow). When compared to the WT group, neurons replaced with the 'L-D&K-D' mutant have enlarged spines and more SEP-GluA1 even at the basal state ('L-D&K-D': Basal), indicating a hyper-excitation status. Interestingly, upon chemLTP induction, these neurons have further enlarged spines and more SEP-GluA1 recruitment ('L-D&K-D': chemLTP) compared to the WT group in the chemLTP state, an observation consistent with the results in Figures 6C and 6D that show less enrichment of the mutant, both at the basal and chemLTP states. Again, neurons replaced with the PSD-95 PDZ binding mutants of SynGAP also displayed larger spines and more GluA1 recruitment upon chemLTP inductions (Figures 7A and 7B). Since the 'L-D&K-D' mutant of SynGAP is easier to be dispersed from synapses than the WT counterpart (Figure 6C), we reasoned that 'L-D&K-D' mutant-containing synapses might be more sensitive in responding to weak chemLTP stimuli. To test this hypothesis, we used a weaker LTP protocol (10 mM glycine stimulation instead of 200 mM Glycine for chemLTP inductions) to investigate whether neurons replaced with the 'L-D&K-D' SynGAP mutant would respond to such weak stimuli. Neurons rescued with the WT SynGAP do not respond to the weaker stimulation. In contrast, neurons with the 'L-D&K-D' SynGAP replacement were responsive to this weaker stimulus both with enlarged spine volumes and with increased GluA1 recruitment (Figures 7C and 7D). This result indicates that the 'L-D&K-D' mutant of SynGAP is more sensitive and more responsive to weak stimuli. Taken together, the formation of SynGAP trimer plays a critical role in anchoring SynGAP to the synapse with proper dynamic modulation and thereby regulates synaptic strength under the normal physiological conditions. Our results also provide a molecular explanation to why SynGAP mutations leading to the disruption of its trimerization or alterations of its PSD-95 binding will lead to neuronal hyperexcitation because of mutation-induced excessive dispersions of SynGAP from synapses." 8/11/2017 Pim - The authors make the case that recruitment of SynGAP gives the PSD gel like properties that may be imporant for recruitment of synaptic proteins and ultimately for synaptic function. |
| Evidence tracking, Biological System: | Cultured neurons Cell-free system |
| Evidence tracking, Protein Targeting: | RNAi / shRNA Over-expression Antibody (detection) |
| Evidence tracking, Experiment Assay: | Confocal Microscopy (generic) Protein-protein interaction (generic) |
| Annotator(s): | Chiara Verpelli (ORCID:0000-0003-2949-9725) Carlo Sala (ORCID:0000-0003-0662-9523) |
| Lab: | CNR Neuroscience Institute Milan and Dept. of Biotechnology and Translational Medicine, University of Milan, 20129 Milan, Italy |
| SynGO annotation ID: | 3681 |
| Dataset release (version): | 20231201 |
| View annotation as GO-CAM model: |  |