| First Author | Choi C | Year | 2022 |
| Journal | Front Mol Neurosci | Volume | 15 |
| Pages | 1017404 | PubMed ID | 36263376 |
| Mgi Jnum | J:330891 | Mgi Id | MGI:7365892 |
| Doi | 10.3389/fnmol.2022.1017404 | Citation | Choi C, et al. (2022) Analyzing the mechanisms that facilitate the subtype-specific assembly of gamma-aminobutyric acid type A receptors. Front Mol Neurosci 15:1017404 |
| abstractText | Impaired inhibitory signaling underlies the pathophysiology of many neuropsychiatric and neurodevelopmental disorders including autism spectrum disorders and epilepsy. Neuronal inhibition is regulated by synaptic and extrasynaptic gamma-aminobutyric acid type A receptors (GABA A Rs), which mediate phasic and tonic inhibition, respectively. These two GABA A R subtypes differ in their function, ligand sensitivity, and physiological properties. Importantly, they contain different alpha subunit isoforms: synaptic GABA A Rs contain the alpha1-3 subunits whereas extrasynaptic GABA A Rs contain the alpha4-6 subunits. While the subunit composition is critical for the distinct roles of synaptic and extrasynaptic GABA A R subtypes in inhibition, the molecular mechanism of the subtype-specific assembly has not been elucidated. To address this issue, we purified endogenous alpha1- and alpha4-containing GABA A Rs from adult murine forebrains and examined their subunit composition and interacting proteins using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) and quantitative analysis. We found that the alpha1 and alpha4 subunits form separate populations of GABA A Rs and interact with distinct sets of binding proteins. We also discovered that the beta3 subunit, which co-purifies with both the alpha1 and alpha4 subunits, has different levels of phosphorylation on serines 408 and 409 (S408/9) between the two receptor subtypes. To understand the role S408/9 plays in the assembly of alpha1- and alpha4-containing GABA A Rs, we examined the effects of S408/9A (alanine) knock-in mutation on the subunit composition of the two receptor subtypes using LC-MS/MS and quantitative analysis. We discovered that the S408/9A mutation results in the formation of novel alpha1alpha4-containing GABA A Rs. Moreover, in S408/9A mutants, the plasma membrane expression of the alpha4 subunit is increased whereas its retention in the endoplasmic reticulum is reduced. These findings suggest that S408/9 play a critical role in determining the subtype-specific assembly of GABA A Rs, and thus the efficacy of neuronal inhibition. |
