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Abstract
Modulation of neurotransmitter exocytosis by activated Gi/o coupled G-protein coupled receptors (GPCRs) is a universal regulatory mechanism used both to avoid overstimulation and to influence circuitry. One of the known modulation mechanisms is the interaction between Gβγ and the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNAREs). There are 5 Gβ and 12 Gγ subunits, but specific Gβγs activated by a given GPCR and the specificity to effectors, such as SNARE, in vivo are not known. Although less studied, Gβγ binding to the exocytic fusion machinery (i.e. SNARE) provides a more direct regulatory mechanism for neurotransmitter release. Here, we review some recent insights in the architecture of the synaptic terminal, modulation of synaptic transmission, and implications of G protein modulation of synaptic transmission in diseases. Numerous presynaptic proteins are involved in the architecture of synaptic terminals, particularly the active zone, and their importance in the regulation of exocytosis is still not completely understood. Further understanding of the Gβγ-SNARE interaction and the architecture and mechanisms of exocytosis may lead to the discovery of novel therapeutic targets to help patients with various disorders such as hypertension, attention-deficit/hyperactivity disorder, post-traumatic stress disorder, and acute/chronic pain.
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Affiliation(s)
- Yun Young Yim
- Department of Pharmacology, Vanderbilt University, Nashville 37232-6600, TN, United States
| | - Zack Zurawski
- Department of Pharmacology, Vanderbilt University, Nashville 37232-6600, TN, United States
| | - Heidi Hamm
- Department of Pharmacology, Vanderbilt University, Nashville 37232-6600, TN, United States.
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Daraio T, Valladolid-Acebes I, Brismar K, Bark C. SNAP-25a and SNAP-25b differently mediate interactions with Munc18-1 and Gβγ subunits. Neurosci Lett 2018; 674:75-80. [PMID: 29548989 DOI: 10.1016/j.neulet.2018.03.024] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2017] [Revised: 03/09/2018] [Accepted: 03/12/2018] [Indexed: 02/06/2023]
Abstract
SNAP-25 is a protein involved in regulated membrane fusion and part of the SNARE complex. It exists as two splicing variants, SNAP-25a and SNAP-25b, which differ in 9 out of 206 amino acids. SNAP-25 together with Syntaxin 1 and VAMP-2 forms the ternary SNARE complex essential for mediating activity-dependent release of hormones and neurotransmitters. The functional difference between SNAP-25a and SNAP-25b is poorly understood as both can participate in SNARE complexes and mediate membrane fusion. However, we recently demonstrated that SNAP-25b-deficiency results in metabolic disease and increased insulin secretion. Here we investigated if SNAP-25a and SNAP-25b differently affect interactions with other SNAREs and SNARE-interacting proteins in mouse hippocampus. Adult mice almost exclusively express the SNAP-25b protein in hippocampus whereas SNAP-25b-deficient mice only express SNAP-25a. Immunoprecipitation studies showed no significant differences in amount of Syntaxin 1 and VAMP-2 co-precipitated with the different SNAP-25 isoforms. In contrast, Munc18-1, that preferentially interacts with SNAP-25 via Syntaxin 1 and/or the trimeric SNARE complex, demonstrated an increased ability to bind protein-complexes containing SNAP-25b. Moreover, we found that both SNAP-25 isoforms co-precipitated the Gβγ subunits of the heterotrimeric G proteins, an interaction known to play a role in presynaptic inhibition. We have identified Gβ1 and Gβ2 as the interacting partners of both SNAP-25 isoforms in mouse hippocampus, but Gβ2 was less efficiently captured by SNAP-25a. These results implicate that the two SNAP-25 isoforms could differently mediate protein interactions outside the ternary SNARE core complex and thereby contribute to modulate neurotransmission.
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Affiliation(s)
- Teresa Daraio
- Department of Molecular Medicine and Surgery, Karolinska Institutet, SE-171 76 Stockholm, Sweden
| | - Ismael Valladolid-Acebes
- Department of Molecular Medicine and Surgery, Karolinska Institutet, SE-171 76 Stockholm, Sweden
| | - Kerstin Brismar
- Department of Molecular Medicine and Surgery, Karolinska Institutet, SE-171 76 Stockholm, Sweden
| | - Christina Bark
- Department of Molecular Medicine and Surgery, Karolinska Institutet, SE-171 76 Stockholm, Sweden.
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Munc18a clusters SNARE-bearing liposomes prior to trans-SNARE zippering. Biochem J 2017; 474:3339-3354. [PMID: 28827281 DOI: 10.1042/bcj20170494] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2017] [Revised: 08/16/2017] [Accepted: 08/17/2017] [Indexed: 12/16/2022]
Abstract
Sec1-Munc18 (SM) proteins co-operate with SNAREs {SNAP [soluble NSF (N-ethylmaleimide-sensitive factor) attachment protein] receptors} to mediate membrane fusion in eukaryotic cells. Studies of Munc18a/Munc18-1/Stxbp1 in neurotransmission suggest that SM proteins accelerate fusion kinetics primarily by activating the partially zippered trans-SNARE complex. However, accumulating evidence has argued for additional roles for SM proteins in earlier steps in the fusion cascade. Here, we investigate the function of Munc18a in reconstituted exocytic reactions mediated by neuronal and non-neuronal SNAREs. We show that Munc18a plays a direct role in promoting proteoliposome clustering, underlying vesicle docking during exocytosis. In the three different fusion reactions examined, Munc18a-dependent clustering requires an intact N-terminal peptide (N-peptide) motif in syntaxin that mediates the binary interaction between syntaxin and Munc18a. Importantly, clustering is preserved under inhibitory conditions that abolish both trans-SNARE complex formation and lipid mixing, indicating that Munc18a promotes membrane clustering in a step that is independent of trans-SNARE zippering and activation.
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Geerts CJ, Mancini R, Chen N, Koopmans FTW, Li KW, Smit AB, van Weering JRT, Verhage M, Groffen AJA. Tomosyn associates with secretory vesicles in neurons through its N- and C-terminal domains. PLoS One 2017; 12:e0180912. [PMID: 28746398 PMCID: PMC5529015 DOI: 10.1371/journal.pone.0180912] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2017] [Accepted: 06/22/2017] [Indexed: 02/03/2023] Open
Abstract
The secretory pathway in neurons requires efficient targeting of cargos and regulatory proteins to their release sites. Tomosyn contributes to synapse function by regulating synaptic vesicle (SV) and dense-core vesicle (DCV) secretion. While there is large support for the presynaptic accumulation of tomosyn in fixed preparations, alternative subcellular locations have been suggested. Here we studied the dynamic distribution of tomosyn-1 (Stxbp5) and tomosyn-2 (Stxbp5l) in mouse hippocampal neurons and observed a mixed diffuse and punctate localization pattern of both isoforms. Tomosyn-1 accumulations were present in axons and dendrites. As expected, tomosyn-1 was expressed in about 75% of the presynaptic terminals. Interestingly, also bidirectional moving tomosyn-1 and -2 puncta were observed. Despite the lack of a membrane anchor these puncta co-migrated with synapsin and neuropeptide Y, markers for respectively SVs and DCVs. Genetic blockade of two known tomosyn interactions with synaptotagmin-1 and its cognate SNAREs did not abolish its vesicular co-migration, suggesting an interplay of protein interactions mediated by the WD40 and SNARE domains. We hypothesize that the vesicle-binding properties of tomosyns may control the delivery, pan-synaptic sharing and secretion of neuronal signaling molecules, exceeding its canonical role at the plasma membrane.
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Affiliation(s)
- Cornelia J. Geerts
- Department of Functional Genomics, Centre for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University, Amsterdam, The Netherlands
| | - Roberta Mancini
- Department of Functional Genomics, Centre for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University, Amsterdam, The Netherlands
| | - Ning Chen
- Molecular and Cellular Neurobiology, Centre for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University, Amsterdam, The Netherlands
| | - Frank T. W. Koopmans
- Department of Functional Genomics, Centre for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University, Amsterdam, The Netherlands
| | - Ka Wan Li
- Molecular and Cellular Neurobiology, Centre for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University, Amsterdam, The Netherlands
| | - August B. Smit
- Molecular and Cellular Neurobiology, Centre for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University, Amsterdam, The Netherlands
| | | | - Matthijs Verhage
- Department of Functional Genomics, Centre for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University, Amsterdam, The Netherlands
- Department of Clinical Genetics, VU Medical Center, Amsterdam, The Netherlands
| | - Alexander J. A. Groffen
- Department of Functional Genomics, Centre for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University, Amsterdam, The Netherlands
- Department of Clinical Genetics, VU Medical Center, Amsterdam, The Netherlands
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Chen J, Chopra R, Hayes C, Morris G, Marla S, Burke J, Xin Z, Burow G. Genome-Wide Association Study of Developing Leaves' Heat Tolerance during Vegetative Growth Stages in a Sorghum Association Panel. THE PLANT GENOME 2017; 10. [PMID: 28724078 DOI: 10.3835/plantgenome2016.09.0091] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Heat stress reduces grain yield and quality worldwide. Enhancing heat tolerance of crops at all developmental stages is one of the essential strategies required for sustaining agricultural production especially as frequency of temperature extremes escalates in response to climate change. Although heat tolerance mechanisms have been studied extensively in model plant species, little is known about the genetic control underlying heat stress responses of crop plants at the vegetative stage under field conditions. To dissect the genetic basis of heat tolerance in sorghum [ (L.) Moench], we performed a genome-wide association study (GWAS) for traits responsive to heat stress at the vegetative stage in an association panel. Natural variation in leaf firing (LF) and leaf blotching (LB) were evaluated separately for 3 yr in experimental fields at three locations where sporadic heat waves occurred throughout the sorghum growing season. We identified nine single-nucleotide polymorphisms (SNPs) that were significantly associated with LF and five SNPs that were associated with LB. Candidate genes near the SNPs were investigated and 14 were directly linked to biological pathways involved in plant stress responses including heat stress response. The findings of this study provide new knowledge on the genetic control of leaf traits responsive to heat stress in sorghum, which could aid in elucidating the genetic and molecular mechanisms of vegetative stage heat tolerance in crops. The results also provide candidate markers for molecular breeding of enhanced heat tolerance in cereal and bioenergy crops.
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Suri M, Evers JMG, Laskowski RA, O'Brien S, Baker K, Clayton-Smith J, Dabir T, Josifova D, Joss S, Kerr B, Kraus A, McEntagart M, Morton J, Smith A, Splitt M, Thornton JM, Wright CF. Protein structure and phenotypic analysis of pathogenic and population missense variants in STXBP1. Mol Genet Genomic Med 2017; 5:495-507. [PMID: 28944233 PMCID: PMC5606886 DOI: 10.1002/mgg3.304] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2017] [Revised: 05/17/2017] [Accepted: 05/20/2017] [Indexed: 01/07/2023] Open
Abstract
Background Syntaxin‐binding protein 1, encoded by STXBP1, is highly expressed in the brain and involved in fusing synaptic vesicles with the plasma membrane. Studies have shown that pathogenic loss‐of‐function variants in this gene result in various types of epilepsies, mostly beginning early in life. We were interested to model pathogenic missense variants on the protein structure to investigate the mechanism of pathogenicity and genotype–phenotype correlations. Methods We report 11 patients with pathogenic de novo mutations in STXBP1 identified in the first 4293 trios of the Deciphering Developmental Disorder (DDD) study, including six missense variants. We analyzed the structural locations of the pathogenic missense variants from this study and the literature, as well as population missense variants extracted from Exome Aggregation Consortium (ExAC). Results Pathogenic variants are significantly more likely to occur at highly conserved locations than population variants, and be buried inside the protein domain. Pathogenic mutations are also more likely to destabilize the domain structure compared with population variants, increasing the proportion of (partially) unfolded domains that are prone to aggregation or degradation. We were unable to detect any genotype–phenotype correlation, but unlike previously reported cases, most of the DDD patients with STXBP1 pathogenic variants did not present with very early‐onset or severe epilepsy and encephalopathy, though all have developmental delay with intellectual disability and most display behavioral problems and suffered seizures in later childhood. Conclusion Variants across STXBP1 that cause loss of function can result in severe intellectual disability with or without seizures, consistent with a haploinsufficiency mechanism. Pathogenic missense mutations act through destabilization of the protein domain, making it prone to aggregation or degradation. The presence or absence of early seizures may reflect ascertainment bias in the literature as well as the broad recruitment strategy of the DDD study.
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Affiliation(s)
- Mohnish Suri
- Nottingham Regional Genetics ServiceNottingham University Hospitals NHS TrustCity Hospital Campus, The Gables, Hucknall RoadNottinghamNG5 1PBUK
| | - Jochem M G Evers
- European Bioinformatics Institute (EMBL-EBI)Wellcome Genome Campus, HinxtonCambridgeCB10 1SDUK
| | - Roman A Laskowski
- European Bioinformatics Institute (EMBL-EBI)Wellcome Genome Campus, HinxtonCambridgeCB10 1SDUK
| | - Sinead O'Brien
- MRC Cognition and Brain Sciences Unit15 Chaucer RoadCambridgeCB2 7EFUK
| | - Kate Baker
- MRC Cognition and Brain Sciences Unit15 Chaucer RoadCambridgeCB2 7EFUK.,Department of Medical GeneticsUniversity of CambridgeCambridge Biomedical CampusCambridgeCB2 0QQUK
| | - Jill Clayton-Smith
- Manchester Centre for Genomic MedicineSt Mary's Hospital, Central Manchester University Hospitals NHS Foundation TrustManchester Academic Health Science CentreManchesterM13 9WLUK
| | - Tabib Dabir
- Northern Ireland Regional Genetics CentreBelfast Health and Social Care TrustBelfast City HospitalLisburn RoadBelfastBT9 7ABUK
| | - Dragana Josifova
- South East Thames Regional Genetics CentreGuy's and St Thomas' NHS Foundation TrustGuy's HospitalGreat Maze PondLondonSE1 9RTUK
| | - Shelagh Joss
- West of Scotland Genetics ServiceQueen Elizabeth University HospitalLaboratory Medicine BuildingGlasgowG51 4TFUK
| | - Bronwyn Kerr
- Manchester Centre for Genomic MedicineSt Mary's Hospital, Central Manchester University Hospitals NHS Foundation TrustManchester Academic Health Science CentreManchesterM13 9WLUK
| | - Alison Kraus
- Yorkshire Regional Genetics ServiceDepartment of Clinical GeneticsLeeds Teaching Hospitals NHS TrustChapel Allerton HospitalChapeltown RoadLeedsLS7 4SAUK
| | - Meriel McEntagart
- South West Thames Regional Genetics CentreSt George's Healthcare NHS TrustSt George's University of LondonCranmer TerraceLondonSW17 0REUK
| | - Jenny Morton
- West Midlands Regional Clinical Genetics Service and Birmingham Health PartnersBirmingham Women's and Children's NHS Foundation TrustBirmingham Women's HospitalMindelsohn Way, EdgbastonBirminghamB15 2TGUK
| | - Audrey Smith
- Yorkshire Regional Genetics ServiceDepartment of Clinical GeneticsLeeds Teaching Hospitals NHS TrustChapel Allerton HospitalChapeltown RoadLeedsLS7 4SAUK
| | - Miranda Splitt
- Northern Genetics ServiceNewcastle upon Tyne Hospitals NHS Foundation TrustInstitute of Human GeneticsInternational Centre for LifeCentral ParkwayNewcastle upon TyneNE1 3BZUK
| | - Janet M Thornton
- European Bioinformatics Institute (EMBL-EBI)Wellcome Genome Campus, HinxtonCambridgeCB10 1SDUK
| | | | - Caroline F Wright
- Wellcome Trust Sanger InstituteWellcome Genome Campus, HinxtonCambridgeCB1 8RQUK.,University of Exeter Medical SchoolRoyal Devon & Exeter HospitalBarrack RoadExeterEX2 5DWUK
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