Biology:SYNGAP1

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Short description: Protein in Homo sapiens


A representation of the 3D structure of the protein myoglobin showing turquoise α-helices.
Generic protein structure example

Synaptic Ras GTPase-activating protein 1, also known as synaptic Ras-GAP 1 or SYNGAP1, is a protein that in humans is encoded by the SYNGAP1 gene.[1][2][3] SYNGAP1 is a ras GTPase-activating protein that is critical for the development of cognition and proper synapse function. Mutations in humans can cause intellectual disability, epilepsy, autism and sensory processing deficits.

Function

SynGAP1 is a complex protein with several functions that may be regulated temporally via complex isoforms.[4] A well-documented function of SynGAP1 involves NMDA receptor-mediated synaptic plasticity and membrane insertion of AMPA receptors through the suppression of upstream signaling pathways.[5] However, SynGAP1 has also been shown to function cooperatively with Unc51.1 in axon formation.[6] One way SynGAP1 affects these processes is through the MAP kinase signaling pathway by attenuation of Ras signalling.[7] However, alternative splicing and multiple translational start sites have been shown to cause opposing effects, illustrating the importance of multiple functional domains that reside within the c- and n-termini. For example, the expression of an α1 or α2 c-terminal variant of SynGAP1 will either increase or decrease synaptic strength, respectively.[4] Overall, SynGAP1 is essential for development and survival, which is evident as knockout mice die perinatally.[8]

Dendritic spine development and maturation

SynGAP1 is shown to localize at the postsynaptic density on the dendritic spines of excitatory synapses.[2] Cultured neurons of SynGAP heterozygotic and homozygotic knockout mice display accelerated maturation of dendritic spines, including an increase in overall spine size, which produces more mushroom shaped and less stubby spines.[5][7][9] Spine heads are enlarged due to the increased phosphorylation of cofilin, leading to a decrease in F-actin severing and turnover.[10] The increased size of the dendritic spines also corresponded to an increase in membrane bound AMPARs or a decrease in silent synapses. These neurons displayed a higher frequency and larger amplitudes of miniature excitatory postsynaptic potentials (mEPSP).[9] Mice models with domain specific mutations led to neonatal hyperactivity of the hippocampal trisynaptic circuit. Mutations had the greatest impact during the first 3 weeks of development, and reversal of mutations in adults did not improve behavior and cognition.[5]

Clinical significance

Several mutations in the SYNGAP1 gene were identified as the cause of intellectual disability. Intellectual disability is sometimes associated with syndromes of other defects caused by the same gene, but SYNGAP1-associated intellectual disability is not; it is therefore called non-syndromic intellectual disability. Since neither of the parents of children with this condition have the mutation, this means it was a sporadic mutation that occurred during division of the parents' gametes (meiosis) or fertilization of the egg. It is a dominant mutation, which means that the individual will be developmentally disabled even if only one allele is mutated.[11]

Mutations in this gene have also been found associated to cases of developmental and epileptic encephalopathies, autism spectrum disorder, and touch-related sensory processing deficits.[12][13][14]

Epilepsy in this disorder is distinctive, combining eyelid myoclonia with absences and myoclonic-atonic seizures. Seizures are often triggered by eating.[15][16]

A causal therapy was the first successful worldwide by the group of Prof. Gerhard Kluger tested at the Schön Klinik in Vogtareuth with statins. In the process, the RAS pathway, which is overactive in SYNGAP1-associated intellectual disability is inhibited by statins. Further clinical studies by the group of Prof. Gerhard Kluger are in preparation.[17]

Interactions

SYNGAP1 has been shown to interact with DLG3[2] and ULK1.[6]

References

  1. ↑ "Entrez Gene: SYNGAP1 synaptic Ras GTPase activating protein 1 homolog (rat)". https://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=8831. 
  2. ↑ 2.0 2.1 2.2 "SynGAP: a synaptic RasGAP that associates with the PSD-95/SAP90 protein family". Neuron 20 (4): 683–91. April 1998. doi:10.1016/S0896-6273(00)81008-9. PMID 9581761. 
  3. ↑ "A synaptic Ras-GTPase activating protein (p135 SynGAP) inhibited by CaM kinase II". Neuron 20 (5): 895–904. May 1998. doi:10.1016/S0896-6273(00)80471-7. PMID 9620694. 
  4. ↑ 4.0 4.1 "SynGAP isoforms exert opposing effects on synaptic strength". Nature Communications 3: 900. June 2012. doi:10.1038/ncomms1900. PMID 22692543. 
  5. ↑ 5.0 5.1 5.2 "Pathogenic SYNGAP1 mutations impair cognitive development by disrupting maturation of dendritic spine synapses". Cell 151 (4): 709–23. November 2012. doi:10.1016/j.cell.2012.08.045. PMID 23141534. 
  6. ↑ 6.0 6.1 "Role of Unc51.1 and its binding partners in CNS axon outgrowth". Genes & Development 18 (5): 541–58. March 2004. doi:10.1101/gad.1151204. PMID 15014045. 
  7. ↑ 7.0 7.1 "SynGAP regulates synaptic strength and mitogen-activated protein kinases in cultured neurons". Proceedings of the National Academy of Sciences of the United States of America 103 (12): 4344–51. March 2006. doi:10.1073/pnas.0600084103. PMID 16537406. 
  8. ↑ "The role of synaptic GTPase-activating protein in neuronal development and synaptic plasticity". The Journal of Neuroscience 23 (4): 1119–24. February 2003. doi:10.1523/JNEUROSCI.23-04-01119.2003. PMID 12598599. 
  9. ↑ 9.0 9.1 "SynGAP regulates spine formation". The Journal of Neuroscience 24 (40): 8862–72. October 2004. doi:10.1523/jneurosci.3213-04.2004. PMID 15470153. 
  10. ↑ "Mechanisms of synapse and dendrite maintenance and their disruption in psychiatric and neurodegenerative disorders". Annual Review of Neuroscience 33: 349–78. July 2010. doi:10.1146/annurev-neuro-060909-153204. PMID 20367247. 
  11. ↑ "Mutations in SYNGAP1 in autosomal nonsyndromic mental retardation". The New England Journal of Medicine 360 (6): 599–605. February 2009. doi:10.1056/NEJMoa0805392. PMID 19196676. 
  12. ↑ "Targeted resequencing in epileptic encephalopathies identifies de novo mutations in CHD2 and SYNGAP1" (in En). Nature Genetics 45 (7): 825–30. July 2013. doi:10.1038/ng.2646. PMID 23708187. 
  13. ↑ "Mutations in SYNGAP1 cause intellectual disability, autism, and a specific form of epilepsy by inducing haploinsufficiency". Human Mutation 34 (2): 385–94. February 2013. doi:10.1002/humu.22248. PMID 23161826. 
  14. ↑ "SYNGAP1 heterozygosity disrupts sensory processing by reducing touch-related activity within somatosensory cortex circuits" (in en). Nature Neuroscience 21 (12): 1–13. December 2018. doi:10.1038/s41593-018-0268-0. ISSN 1546-1726. PMID 30455457. 
  15. ↑ "SYNGAP1 encephalopathy" (in en). Neurology 92 (2): e96–e107. 2018-12-12. doi:10.1212/WNL.0000000000006729. ISSN 0028-3878. PMID 30541864. 
  16. ↑ Stülpnagel, Celina von; Hartlieb, Till; Borggräfe, Ingo et al. (2019-02-01). "Chewing induced reflex seizures ("eating epilepsy") and eye closure sensitivity as a common feature in pediatric patients with SYNGAP1 mutations: Review of literature and report of 8 cases" (in en). Seizure: European Journal of Epilepsy 65: 131–137. doi:10.1016/j.seizure.2018.12.020. ISSN 1059-1311. PMID 30685520. https://www.seizure-journal.com/article/S1059-1311(18)30466-7/abstract. 
  17. ↑ "Positive Short-Term Effect of Low-Dose Rosuvastatin in a Patient with SYNGAP1-Associated Epilepsy". Neuropediatrics 50 (4): 266–267. August 2019. doi:10.1055/s-0039-1681066. PMID 30875700. 

Further reading

External links

  • Overview of all the structural information available in the PDB for UniProt: F6SEU4 (Mouse Ras/Rap GTPase-activating protein SynGAP) at the PDBe-KB.



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