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Bode A, Wood SE, Mullins JGL, Keramidas A, Cushion TD, Thomas RH, Pickrell WO, Drew CJG, Masri A, Jones EA, Vassallo G, Born AP, Alehan F, Aharoni S, Bannasch G, Bartsch M, Kara B, Krause A, Karam EG, Matta S, Jain V, Mandel H, Freilinger M, Graham GE, Hobson E, Chatfield S, Vincent-Delorme C, Rahme JE, Afawi Z, Berkovic SF, Howell OW, Vanbellinghen JF, Rees MI, Chung SK, Lynch JW. New hyperekplexia mutations provide insight into glycine receptor assembly, trafficking, and activation mechanisms. J Biol Chem 2013; 288:33745-33759. [PMID: 24108130 DOI: 10.1074/jbc.m113.509240] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Hyperekplexia is a syndrome of readily provoked startle responses, alongside episodic and generalized hypertonia, that presents within the first month of life. Inhibitory glycine receptors are pentameric ligand-gated ion channels with a definitive and clinically well stratified linkage to hyperekplexia. Most hyperekplexia cases are caused by mutations in the α1 subunit of the human glycine receptor (hGlyR) gene (GLRA1). Here we analyzed 68 new unrelated hyperekplexia probands for GLRA1 mutations and identified 19 mutations, of which 9 were novel. Electrophysiological analysis demonstrated that the dominant mutations p.Q226E, p.V280M, and p.R414H induced spontaneous channel activity, indicating that this is a recurring mechanism in hGlyR pathophysiology. p.Q226E, at the top of TM1, most likely induced tonic activation via an enhanced electrostatic attraction to p.R271 at the top of TM2, suggesting a structural mechanism for channel activation. Receptors incorporating p.P230S (which is heterozygous with p.R65W) desensitized much faster than wild type receptors and represent a new TM1 site capable of modulating desensitization. The recessive mutations p.R72C, p.R218W, p.L291P, p.D388A, and p.E375X precluded cell surface expression unless co-expressed with α1 wild type subunits. The recessive p.E375X mutation resulted in subunit truncation upstream of the TM4 domain. Surprisingly, on the basis of three independent assays, we were able to infer that p.E375X truncated subunits are incorporated into functional hGlyRs together with unmutated α1 or α1 plus β subunits. These aberrant receptors exhibit significantly reduced glycine sensitivity. To our knowledge, this is the first suggestion that subunits lacking TM4 domains might be incorporated into functional pentameric ligand-gated ion channel receptors.
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Affiliation(s)
- Anna Bode
- University of Queensland, Queensland Brain Institute and School of Biomedical Sciences, Queensland 4072, Australia
| | - Sian-Elin Wood
- Department of Neurology Research and Molecular Neuroscience, Institute of Life Science, College of Medicine, Swansea University Swansea SA2 8PP, United Kingdom
| | - Jonathan G L Mullins
- Department of Neurology Research and Molecular Neuroscience, Institute of Life Science, College of Medicine, Swansea University Swansea SA2 8PP, United Kingdom
| | - Angelo Keramidas
- University of Queensland, Queensland Brain Institute and School of Biomedical Sciences, Queensland 4072, Australia
| | - Thomas D Cushion
- Department of Neurology Research and Molecular Neuroscience, Institute of Life Science, College of Medicine, Swansea University Swansea SA2 8PP, United Kingdom
| | - Rhys H Thomas
- Department of Neurology Research and Molecular Neuroscience, Institute of Life Science, College of Medicine, Swansea University Swansea SA2 8PP, United Kingdom; Wales Epilepsy Research Network, College of Medicine, Swansea University Swansea SA2 8PP, United Kingdom
| | - William O Pickrell
- Department of Neurology Research and Molecular Neuroscience, Institute of Life Science, College of Medicine, Swansea University Swansea SA2 8PP, United Kingdom; Wales Epilepsy Research Network, College of Medicine, Swansea University Swansea SA2 8PP, United Kingdom
| | - Cheney J G Drew
- Department of Neurology Research and Molecular Neuroscience, Institute of Life Science, College of Medicine, Swansea University Swansea SA2 8PP, United Kingdom; Wales Epilepsy Research Network, College of Medicine, Swansea University Swansea SA2 8PP, United Kingdom
| | - Amira Masri
- Department of Paediatrics, Division of Child Neurology, Faculty of Medicine, University of Jordan, Amman 11942, Jordan
| | - Elizabeth A Jones
- Manchester Centre for Genomic Medicine, Central Manchester University Hospitals National Health Service Foundation Trust, Manchester Academic Health Sciences Centre, Manchester M13 9WL, United Kingdom; Manchester Centre for Genomic Medicine, Institute of Human Development, Faculty of Medical and Human Sciences, University of Manchester, Manchester Academic Health Sciences Centre, Manchester M13 9WL, United Kingdom
| | - Grace Vassallo
- Royal Manchester Children's Hospital, Central Manchester University Hospitals National Health Service Foundation Trust, Manchester Academic Health Sciences Centre, Manchester M13 9WL, United Kingdom
| | - Alfred P Born
- Department of Pediatrics, Copenhagen University Hospital, Rigshospitalet, 2100 Copenhagen, Denmark
| | - Fusun Alehan
- Department of Pediatrics, Division of Child Neurology, Faculty of Medicine, Basşkent University, 06990 Ankara, Turkey
| | - Sharon Aharoni
- Institute of Pediatric Neurology, Schneider Children's Medical Center of Israel, Petah Tikva 49202, Israel; Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv 69987, Israel
| | - Gerald Bannasch
- Neurology Department, Affinity Medical Group, Menasha, Wisconsin 54952
| | - Marius Bartsch
- Department of Neonatology, University Medical Center of the Johannes Gutenberg University Mainz, D-55099 Mainz, Germany
| | - Bulent Kara
- Kocaeli University Medical Faculty, Department of Pediatrics, Division of Child Neurology, 41380 Kocaeli, Turkey
| | - Amanda Krause
- Division of Human Genetics, National Health Laboratory Service, and School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, 2000 Johannesburg, South Africa
| | - Elie G Karam
- Department of Psychiatry and Clinical Psychology, Saint George Hospital University Medical Center, Balamand University, Faculty of Medicine, Beirut 1100 2807, Lebanon
| | - Stephanie Matta
- Department of Psychiatry and Clinical Psychology, Saint George Hospital University Medical Center, Balamand University, Faculty of Medicine, Beirut 1100 2807, Lebanon
| | - Vivek Jain
- Royal Children's Hospital Melbourne, Children's Neuroscience Centre, Royal Children's Hospital, Victoria 3052, Australia
| | - Hanna Mandel
- Metabolic Unit, Meyer Children's Hospital, Rambam Medical Center, Technion Faculty of Medicine, Haifa 31096, Israel
| | - Michael Freilinger
- Department of Pediatrics and Adolescent Medicine, Medical University of Vienna, 1090 Vienna, Austria
| | - Gail E Graham
- Department of Genetics, Children's Hospital of Eastern Ontario, Ottawa, Ontario K1H 8L1, Canada
| | - Emma Hobson
- Yorkshire Regional Genetic Service, Chapel Allerton Hospital, Leeds, West Yorkshire LS9 7TF, United Kingdom
| | - Sue Chatfield
- Neonatal Unit, Bradford Royal Infirmary, Bradford, West Yorkshire BD9 6RJ, United Kingdom
| | | | | | - Zaid Afawi
- Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel
| | - Samuel F Berkovic
- Epilepsy Research Centre, Melbourne Brain Centre, Austin Health, Heidelberg 3084, Victoria, Australia
| | - Owain W Howell
- Department of Neurology Research and Molecular Neuroscience, Institute of Life Science, College of Medicine, Swansea University Swansea SA2 8PP, United Kingdom; Wales Epilepsy Research Network, College of Medicine, Swansea University Swansea SA2 8PP, United Kingdom
| | | | - Mark I Rees
- Department of Neurology Research and Molecular Neuroscience, Institute of Life Science, College of Medicine, Swansea University Swansea SA2 8PP, United Kingdom; Wales Epilepsy Research Network, College of Medicine, Swansea University Swansea SA2 8PP, United Kingdom
| | - Seo-Kyung Chung
- Department of Neurology Research and Molecular Neuroscience, Institute of Life Science, College of Medicine, Swansea University Swansea SA2 8PP, United Kingdom; Wales Epilepsy Research Network, College of Medicine, Swansea University Swansea SA2 8PP, United Kingdom
| | - Joseph W Lynch
- University of Queensland, Queensland Brain Institute and School of Biomedical Sciences, Queensland 4072, Australia.
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