title: Grp94 Protein Delivers γ-Aminobutyric Acid Type A (GABAA) Receptors to Hrd1 Protein-mediated Endoplasmic Reticulum-associated Degradation.
abstract: Proteostasis maintenance of γ-aminobutyric acid type A (GABAA) receptors dictates their function in controlling neuronal inhibition in mammalian central nervous systems. However, as a multisubunit, multispan, integral membrane protein, even wild type subunits of GABAA receptors fold and assemble inefficiently in the endoplasmic reticulum (ER). Unassembled and misfolded subunits undergo ER-associated degradation (ERAD), but this degradation process remains poorly understood for GABAA receptors. Here, using the α1 subunits of GABAA receptors as a model substrate, we demonstrated that Grp94, a metazoan-specific Hsp90 in the ER lumen, uses its middle domain to interact with the α1 subunits and positively regulates their ERAD. OS-9, an ER-resident lectin, acts downstream of Grp94 to further recognize misfolded α1 subunits in a glycan-dependent manner. This delivers misfolded α1 subunits to the Hrd1-mediated ubiquitination and the valosin-containing protein-mediated extraction pathway. Repressing the initial ERAD recognition step by inhibiting Grp94 enhances the functional surface expression of misfolding-prone α1(A322D) subunits, which causes autosomal dominant juvenile myoclonic epilepsy. This study clarifies a Grp94-mediated ERAD pathway for GABAA receptors, which provides a novel way to finely tune their function in physiological and pathophysiological conditions.
authors.affiliation: From the Department of Physiology and Biophysics.
authors.forename: Xiao-Jing
authors.initials: XJ
authors.lastname: Di
authors.affiliation: Center for Proteomics and Bioinformatics and Department of Epidemiology and Biostatistics, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106.
authors.forename: Ya-Juan
authors.initials: YJ
authors.lastname: Wang
authors.affiliation: From the Department of Physiology and Biophysics.
authors.forename: Dong-Yun
authors.initials: DY
authors.lastname: Han
authors.affiliation: From the Department of Physiology and Biophysics.
authors.forename: Yan-Lin
authors.initials: YL
authors.lastname: Fu
authors.affiliation: the Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019, and.
authors.forename: Adam S
authors.initials: AS
authors.lastname: Duerfeldt
authors.affiliation: the Department of Medicinal Chemistry, University of Kansas, Lawrence, Kansas 66045.
authors.forename: Brian S J
authors.initials: BS
authors.lastname: Blagg
authors.affiliation: From the Department of Physiology and Biophysics, tingwei.mu@case.edu.
authors.forename: Ting-Wei
authors.identifier: http://orcid.org/0000-0002-6419-9296
authors.initials: TW
authors.lastname: Mu
mesh_terms: D019943:Amino Acid Substitution; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism*; D060746:Endoplasmic Reticulum-Associated Degradation / Q000502:physiology*; D057809:HEK293 Cells; D006801:Humans; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D020125:Mutation, Missense; D059748:Proteolysis; D011963:Receptors, GABA-A / Q000235:genetics / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination / Q000502:physiology
chemical_list: D008562:Membrane Glycoproteins; D011963:Receptors, GABA-A; C053387:endoplasmin; C482345:SYVN1 protein, human; D044767:Ubiquitin-Protein Ligases
keywords: Cys-loop receptor; Grp94; Hrd1; OS-9; VCP; endoplasmic reticulum-associated protein degradation (ERAD); epilepsy; protein misfolding; proteostasis; γ-aminobutyric acid (GABA)