title: Differential protein structural disturbances and suppression of assembly partners produced by nonsense GABRG2 epilepsy mutations: implications for disease phenotypic heterogeneity.
abstract: Mutations in GABAAreceptor subunit genes are frequently associated with epilepsy, and nonsense mutations in GABRG2 are associated with several epilepsy syndromes including childhood absence epilepsy, generalized tonic clonic seizures and the epileptic encephalopathy, Dravet syndrome. The molecular basis for the phenotypic heterogeneity of mutations is unclear. Here we focused on three nonsense mutations in GABRG2 (GABRG2(R136*), GABRG2(Q390*) and GABRG2(W429*)) associated with epilepsies of different severities. Structural modeling and structure-based analysis indicated that the surface of the wild-type γ2 subunit was naturally hydrophobic, which is suitable to be buried in the cell membrane. Different mutant γ2 subunits had different stabilities and different interactions with their wild-type subunit binding partners because they adopted different conformations and had different surface hydrophobicities and different tendency to dimerize. We utilized flow cytometry and biochemical approaches in combination with lifted whole cell patch-clamp recordings. We demonstrated that the truncated subunits had no to minimal surface expression and unchanged or reduced surface expression of wild-type partnering subunits. The amplitudes of GABA-evoked currents from the mutant α1β2γ2(R136*), α1β2γ2(Q390*) and α1β2γ2(W429*) receptors were reduced compared to the currents from α1β2γ2 receptors but with differentially reduced levels. This thus suggests differential protein structure disturbances are correlated with disease severity.
authors.affiliation: Department of Computer Science and Christopher S. Bond Life Sciences Center, University of Missouri, Columbia, MO, 65211, USA.
authors.forename: Juexin
authors.initials: J
authors.lastname: Wang
authors.affiliation: Graduate Program of Neuroscience, Vanderbilt University, Nashville, TN 37212, USA.
authors.forename: Dingding
authors.initials: D
authors.lastname: Shen
authors.affiliation: Department of Neurology, Vanderbilt University Medical Center, Nashville, TN 37212, USA.
authors.forename: Geqing
authors.initials: G
authors.lastname: Xia
authors.affiliation: Department of Neurology, Vanderbilt University Medical Center, Nashville, TN 37212, USA.
authors.forename: Wangzhen
authors.initials: W
authors.lastname: Shen
authors.affiliation: Department of Neurology, Vanderbilt University Medical Center, Nashville, TN 37212, USA.|Department of Molecular Physiology and Biophysics, School of Medicine, Vanderbilt University, Nashville, TN 37212, USA.|Department of Pharmacology, School of Medicine, Vanderbilt University, Nashville, TN 37212, USA.|Vanderbilt Brain Institute, Vanderbilt University, Nashville, TN 37212, USA.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Macdonald
authors.affiliation: Department of Computer Science and Christopher S. Bond Life Sciences Center, University of Missouri, Columbia, MO, 65211, USA.
authors.forename: Dong
authors.initials: D
authors.lastname: Xu
authors.affiliation: Department of Neurology, Vanderbilt University Medical Center, Nashville, TN 37212, USA.|Vanderbilt Brain Institute, Vanderbilt University, Nashville, TN 37212, USA.
authors.forename: Jing-Qiong
authors.initials: JQ
authors.lastname: Kang
mesh_terms: D001665:Binding Sites; D002462:Cell Membrane / Q000378:metabolism / Q000473:pathology; D018389:Codon, Nonsense; D004831:Epilepsies, Myoclonic / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D004832:Epilepsy, Absence / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D005071:Evoked Potentials / Q000502:physiology; D015870:Gene Expression; D057809:HEK293 Cells; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D062105:Molecular Docking Simulation; D018408:Patch-Clamp Techniques; D010641:Phenotype; D011485:Protein Binding; D000072756:Protein Conformation, alpha-Helical; D000072757:Protein Conformation, beta-Strand; D054730:Protein Interaction Domains and Motifs; D055503:Protein Multimerization; D021122:Protein Subunits / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011963:Receptors, GABA-A / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012640:Seizures / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D012720:Severity of Illness Index; D040681:Structural Homology, Protein; D014162:Transfection
chemical_list: D018389:Codon, Nonsense; C546279:GABRG2 protein, human; D021122:Protein Subunits; D011963:Receptors, GABA-A