title: Aggregation Limits Surface Expression of Homomeric GluA3 Receptors.
abstract: AMPA receptors are glutamate-gated cation channels assembled from GluA1-4 subunits and have properties that are strongly dependent on the subunit composition. The subunits have different propensities to form homomeric or various heteromeric receptors expressed on cell surface, but the underlying mechanisms are still poorly understood. Here, we examined the biochemical basis for the poor ability of GluA3 subunits to form homomeric receptors, linked previously to two amino acid residues, Tyr-454 and Arg-461, in its ligand binding domain (LBD). Surface expression of GluA3 was improved by co-assembly with GluA2 but not with stargazin, a trafficking chaperone and modulator of AMPA receptors. The secretion efficiency of GluA2 and GluA3 LBDs paralleled the transport difference between the respective full-length receptors and was similarly dependent on Tyr-454/Arg-461 but not on LBD stability. In comparison to GluA2, GluA3 homomeric receptors showed a strong and Tyr-454/Arg-461-dependent tendency to aggregate both in the macroscopic scale measured as lower solubility in nonionic detergent and in the microscopic scale evident as the preponderance of hydrodynamically large structures in density gradient centrifugation and native gel electrophoresis. We conclude that the impaired surface expression of homomeric GluA3 receptors is caused by nonproductive assembly and aggregation to which LBD residues Tyr-454 and Arg-461 strongly contribute. This aggregation inhibits the entry of newly synthesized GluA3 receptors to the secretory pathway.
authors.affiliation: From the Department of Biosciences, Division of Biochemistry and Biotechnology, University of Helsinki, Helsinki FI-00014, Finland.
authors.forename: Sarah K
authors.initials: SK
authors.lastname: Coleman
authors.affiliation: From the Department of Biosciences, Division of Biochemistry and Biotechnology, University of Helsinki, Helsinki FI-00014, Finland.
authors.forename: Ying
authors.initials: Y
authors.lastname: Hou
authors.affiliation: From the Department of Biosciences, Division of Biochemistry and Biotechnology, University of Helsinki, Helsinki FI-00014, Finland.
authors.forename: Marina
authors.initials: M
authors.lastname: Willibald
authors.affiliation: From the Department of Biosciences, Division of Biochemistry and Biotechnology, University of Helsinki, Helsinki FI-00014, Finland.
authors.forename: Artur
authors.initials: A
authors.lastname: Semenov
authors.affiliation: From the Department of Biosciences, Division of Biochemistry and Biotechnology, University of Helsinki, Helsinki FI-00014, Finland.
authors.forename: Tommi
authors.initials: T
authors.lastname: Möykkynen
authors.affiliation: From the Department of Biosciences, Division of Biochemistry and Biotechnology, University of Helsinki, Helsinki FI-00014, Finland kari.keinanen@helsinki.fi.
authors.forename: Kari
authors.initials: K
authors.lastname: Keinänen
mesh_terms: D005786:Gene Expression Regulation; D057809:HEK293 Cells; D006801:Humans; D066329:Protein Aggregates; D017434:Protein Structure, Tertiary; D018091:Receptors, AMPA / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D066329:Protein Aggregates; D018091:Receptors, AMPA; C104723:glutamate receptor ionotropic, AMPA 3
keywords: ionotropic glutamate receptor; protein aggregation; protein assembly; protein folding; protein trafficking; surface expression; α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPA receptor, AMPAR)