GABRB3 Mutation, G32R, Associated with Childhood Absence Epilepsy Alters α1β3γ2L γ-Aminobutyric Acid Type A (GABAA) Receptor Expression and Channel Gating

Gurba, Katharine N.; Hernández, Ciria C.; Hu, Ningning; Macdonald, Robert L.

doi:10.1074/jbc.m111.332528

Cited by 54 publications

(49 citation statements)

References 48 publications

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“…Due to the inefficient assembly of mutant γ2 subunit-containing pentameric receptors, receptors with a different stoichiometry (α1β2 dimeric receptors) were able to be assembled. We previously reported two other mutations within structural loops contributing to interface interactions with similar fates: the β3 subunit mutation G32R located at the γ+/β− subunit interface (Gurba et al, 2012), and the γ2 subunit mutation R177G located at the α+/γ− interface (Audenaert et al, 2006). Both GABRB3(G32R) and GABRG2(R177G) mutations were shown to decrease surface levels of mutant γ2L subunits and increase surface levels of αβ heteropentamers and/or β3 homopentamers, indicating a common molecular mechanism shared by this group of mutations.…”

Section: Discussionmentioning

confidence: 99%

Three epilepsy-associated GABRG2 missense mutations at the γ+/β− interface disrupt GABAA receptor assembly and trafficking by similar mechanisms but to different extents

Huang

Hernández

et al. 2014

Neurobiology of Disease

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We compared the effects of three missense mutations in the GABAA receptor γ2 subunit on GABAA receptor assembly, trafficking and function in HEK293T cells cotransfected with α1, β2, and wildtype or mutant γ2 subunits. The mutations R82Q and P83S were identified in families with genetic epilepsy with febrile seizures plus (GEFS+), and N79S was found in a single patient with generalized tonic-clonic seizures (GTCS). Although all three mutations were located in an N terminal loop that contributes to the γ+/β− subunit-subunit interface, we found that each mutation impaired GABAA receptor assembly to a different extent. The γ2(R82Q) and γ2(P83S) subunits had reduced α1β2γ2 receptor surface expression due to impaired assembly into pentamers, endoplasmic reticulum (ER) retention and degradation. In contrast, γ2(N79S) subunits were efficiently assembled into GABAA receptors with only minimally altered receptor trafficking, suggesting that N79S was a rare or susceptibility variant rather than an epilepsy mutation. Increased structural variability at assembly motifs was predicted by R82Q and P83S, but not N79S, substitution, suggesting that R82Q and P83S substitutions were less tolerated. Membrane proteins with missense mutations that impair folding and assembly often can be “rescued” by decreased temperatures. We coexpressed wildtype or mutant γ2 subunits with α1 and β2 subunits and found increased surface and total levels of both wildtype and mutant γ2 subunits after decreasing the incubation temperature to 30 °C for 24 hours, suggesting that lower temperatures increased GABAA receptor stability. Thus epilepsy-associated mutations N79S, R82Q and P83S disrupted GABAA receptor assembly to different extents, an effect that could be potentially rescued by facilitating protein folding and assembly.

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Section: Discussionmentioning

confidence: 99%

Three epilepsy-associated GABRG2 missense mutations at the γ+/β− interface disrupt GABAA receptor assembly and trafficking by similar mechanisms but to different extents

Huang

Hernández

et al. 2014

Neurobiology of Disease

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“…Previous studies have shown that altered N-glycosylation of some GABA A R subunits in model systems affects the processing, assembly, receptor stability, and cell surface expression of mature GABA A Rs, as well as affecting channel gating properties and receptor function (Buller et al, 1994;Gurba et al, 2012;Lo et al, 2010;Tanaka et al, 2008). N-glycosylation has a functional role regulating forward trafficking of proteins along the secretory pathway from the ER through the Golgi before vesicular transport to the plasma membrane.…”

Section: Discussionmentioning

confidence: 99%

“…Mutations of consensus sequences on the b2 subunit inhibiting N-glycosylation have been shown to decrease peak current amplitude and mean channel open time of GABA A Rs and, in an N-glycosylation consensus sequence-specific manner, have variable effects on subunit stability, assembly of receptors in the ER, and expression of N-glycosylation-deficient b2 subunit-containing receptors in the plasma membrane (Lo et al, 2010). It has been postulated that aberrant glycosylation of specific GABA A R subunits may lead to altered protein folding and tertiary structure, causing the assembly of correctly N-glycosylated subunits to be more energetically favorable and altering GABA A R subunit stoichiometry in the plasma membrane (Gurba et al, 2012). Alternatively, it has been suggested that incorrect N-glycosylation may impair receptor trafficking to the plasma membrane, reducing GABA-evoked currents and decreasing the efficacy of GABAergic signaling (Tanaka et al, 2008).…”

Section: Discussionmentioning

confidence: 99%

N-Glycosylation of GABAA Receptor Subunits is Altered in Schizophrenia

Mueller

Haroutunian

Meador‐Woodruff

2013

Neuropsychopharmacol

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The molecular mechanisms of schizophrenia have been under investigation for decades; however, the exact causes of this debilitating neuropsychiatric disorder are still unknown. Previous studies have identified multiple affected neurotransmitter systems, brain regions, and cell types, each making a unique contribution to symptom presentation and pathophysiology. Numerous studies have identified gene and protein expression changes in schizophrenia, but the role of post-translational modifications, specifically N-glycosylation, has only recently become a target of investigation. N-glycosylation of molecules associated with glutamatergic neurotransmission is disrupted in schizophrenia, but it was unknown if these alterations are exclusive to the glutamatergic system or due to a more generalized deficit.In normal human cortex, we found evidence for N-glycosylation of the α1, β1, and β2 γ-aminobutyric type A receptor (GABAAR) subunits using deglycosylation protein shift assays. This was confirmed with lectin affinity assays that revealed glycan attachment on the α1, α4, and β1-3 GABAAR subunits. Examining GABAAR subunit N-glycosylation in matched pairs of schizophrenia (N=14) and comparison (N=14) of superior temporal gyrus revealed a smaller molecular mass of immature N-glycans on the α1 subunit, more immature N-glycosylation of the 49-kDa β1 subunit isoform, and altered total N-glycosylation of the β2 GABAAR subunit in schizophrenia. Measures of altered N-glycosylation of the β1 and β2 subunits were confounded by an increased apparent molecular mass of all β1 and β2 subunit isoforms in schizophrenia. Although N-glycosylation of α1, β1, and β2 were all changed in schizophrenia, the concentrations of GABAAR subunits themselves were unchanged. These findings suggest that disruptions of N-glycosylation in schizophrenia are not exclusive to glutamate and may indicate a potential disruption of a central cell signaling process in this disorder.

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“…Although ab-heteromers lacking the g subunit are functional and exhibit higher potency (e.g., lower EC 50 ) for GABA than abg assemblies, the loss of the g subunit impairs the targeting of ab receptors to the synapse via the loss of interactions with the GABARAP-gephyrin trafficking-scaffolding machinery. In addition, b3(P11S), b3(S15F), and b3(G32R) all result in N-linked glycosylation errors, impairing normal GABA receptor-mediated inhibition, resulting in GEFS1 and/or DS (Tanaka et al, 2008;Gurba et al, 2012). In addition to those noted above, 10 more mutations in the most abundant a subunit, a1, have been linked with idiopathic epilepsies, Dravet syndrome, and epileptic encephalopathies.…”

Section: Gaba a Receptorsmentioning

confidence: 95%

“…However, as with the majority of GABR SNPs, more data are needed to specifically understand how each SNP leads to a change in GABAergic function. If the same approach taken in the evaluation of epilepsy-linked mutations can be applied here (e.g., Gallagher et al, 2007;Gurba et al, 2012), our understanding of addiction could be substantially enhanced.…”

Section: Gaba a Receptorsmentioning

confidence: 99%

Ionotropic GABA and Glutamate Receptor Mutations and Human Neurologic Diseases

Yuan¹,

Low²,

Moody³

et al. 2015

Mol Pharmacol

186

176

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The advent of whole exome/genome sequencing and the technology-driven reduction in the cost of next-generation sequencing as well as the introduction of diagnostic-targeted sequencing chips have resulted in an unprecedented volume of data directly linking patient genomic variability to disorders of the brain. This information has the potential to transform our understanding of neurologic disorders by improving diagnoses, illuminating the molecular heterogeneity underlying diseases, and identifying new targets for therapeutic treatment. There is a strong history of mutations in GABA receptor genes being involved in neurologic diseases, particularly the epilepsies. In addition, a substantial number of variants and mutations have been found in GABA receptor genes in patients with autism, schizophrenia, and addiction, suggesting potential links between the GABA receptors and these conditions. A new and unexpected outcome from sequencing efforts has been the surprising number of mutations found in glutamate receptor subunits, with the GRIN2A gene encoding the GluN2A N-methyl-D-aspartate receptor subunit being most often affected. These mutations are associated with multiple neurologic conditions, for which seizure disorders comprise the largest group. The GluN2A subunit appears to be a locus for epilepsy, which holds important therapeutic implications. Virtually all a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor mutations, most of which occur within GRIA3, are from patients with intellectual disabilities, suggesting a link to this condition. Similarly, the most common phenotype for kainate receptor variants is intellectual disability. Herein, we summarize the current understanding of disease-associated mutations in ionotropic GABA and glutamate receptor families, and discuss implications regarding the identification of human mutations and treatment of neurologic diseases.

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GABRB3 Mutation, G32R, Associated with Childhood Absence Epilepsy Alters α1β3γ2L γ-Aminobutyric Acid Type A (GABAA) Receptor Expression and Channel Gating

Cited by 54 publications

References 48 publications

Three epilepsy-associated GABRG2 missense mutations at the γ+/β− interface disrupt GABAA receptor assembly and trafficking by similar mechanisms but to different extents

Three epilepsy-associated GABRG2 missense mutations at the γ+/β− interface disrupt GABAA receptor assembly and trafficking by similar mechanisms but to different extents

N-Glycosylation of GABAA Receptor Subunits is Altered in Schizophrenia

Ionotropic GABA and Glutamate Receptor Mutations and Human Neurologic Diseases

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