title: Agonist binding to the GluK5 subunit is sufficient for functional surface expression of heteromeric GluK2/GluK5 kainate receptors.
abstract: Trafficking of ionotropic glutamate receptors to the plasma membrane commonly requires occupation of the agonist binding sites. This quality control check does not typically involve receptor activation, as binding by competitive antagonists or to non-functional channels may also permit surface expression. The tetrameric kainate receptors can be assembled from five different subunits (GluK1-GluK5). While the "low-affinity" GluK1-3 subunits are able to produce functional homomeric receptors, the "high-affinity" GluK4 and GluK5 subunits require co-assembly with GluK1, 2, or 3 for surface expression. These two different types of subunits have distinct functional roles in the receptor. Therefore, we examined the relative importance of occupancy of the agonist site of the GluK2 or GluK5 subunit for surface expression of heteromeric receptors. We created subunits with a mutation within the S2 ligand-binding domain which decreased agonist affinity. Mutations at this site reduced functional surface expression of homomeric GluK2 receptors, but surface expression of these receptors could be increased with either a competitive antagonist or co-assembly with wild-type GluK5. In contrast, mutations in the GluK5 subunit reduced the production of functional heteromeric receptors at the membrane, and could not be rescued with either an antagonist or wild-type GluK2. These findings indicate that ligand binding to only the GluK5 subunit is both necessary and sufficient to allow trafficking of recombinant GluK2/K5 heteromers to the cell membrane, but that occupancy of the GluK2 site alone is not. Our results suggest a distinct role for the GluK5 subunit in regulating surface expression of heteromeric kainate receptors.
authors: Department of Pharmacology, Physiology and Neuroscience, University of South Carolina School of Medicine, Columbia, SC, 29208, USA, jfisher@uscmed.sc.edu.
authors: Janet L
authors: JL
authors: Fisher
authors: Paul R
authors: PR
authors: Housley
mesh_terms: D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D005971:Glutamates / Q000494:pharmacology; D057809:HEK293 Cells; D006801:Humans; D008024:Ligands; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D011485:Protein Binding / Q000187:drug effects; D055503:Protein Multimerization / Q000187:drug effects; D021122:Protein Subunits / Q000819:agonists* / Q000737:chemistry / Q000378:metabolism; D051381:Rats; D018092:Kainic Acid Receptors / Q000819:agonists* / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D000097806:GluK2 Kainate Receptor
chemical_list: D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D005971:Glutamates; D008024:Ligands; D050505:Mutant Proteins; D021122:Protein Subunits; D018092:Kainic Acid Receptors; D000097806:GluK2 Kainate Receptor
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