title: Ligand-binding domain determines endoplasmic reticulum exit of AMPA receptors.
abstract: AMPA receptors (AMPARs) are tetrameric ion channels that mediate rapid glutamate signaling in neurons and many non-neuronal cell types. Endoplasmic reticulum (ER) quality control mechanisms permit only correctly folded functional receptors to be delivered to the cell surface. We analyzed the biosynthetic maturation and transport of all 12 GluA1-4 subunit splice variants as homomeric receptors and observed robust isoform-dependent differences in ER exit competence and surface expression. In contrast to inefficient ER exit of both GluA3 splice forms and the flop variants of GluA1 and GluA4, prominent plasma membrane expression was observed for the other AMPAR isoforms. Surprisingly, deletion of the entire N-terminal domain did not alter the transport phenotype, nor did the different cytosolic C-terminal tail splice variants. Detailed analysis of mutant receptors led to the identification of distinct residues in the ligand-binding domain as primary determinants for isoform-specific maturation. Considered together with the essential role of bound agonist, our findings reveal the ligand-binding domain as the critical quality control target in AMPAR biogenesis.
authors.affiliation: Department of Biosciences, Division of Biochemistry, Viikki Biocenter, University of Helsinki, FI-00014 University of Helsinki, Finland.
authors.forename: Sarah K
authors.initials: SK
authors.lastname: Coleman
authors.forename: Tommi
authors.initials: T
authors.lastname: Möykkynen
authors.forename: Sami
authors.initials: S
authors.lastname: Hinkkuri
authors.forename: Lauri
authors.initials: L
authors.lastname: Vaahtera
authors.forename: Esa R
authors.initials: ER
authors.lastname: Korpi
authors.forename: Olli T
authors.initials: OT
authors.lastname: Pentikäinen
authors.forename: Kari
authors.initials: K
authors.lastname: Keinänen
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D019556:COS Cells; D002462:Cell Membrane / Q000378:metabolism; D002522:Chlorocebus aethiops; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D015151:Immunoblotting; D008024:Ligands; D008856:Microscopy, Fluorescence; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport; D018091:Receptors, AMPA / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
chemical_list: D008024:Ligands; D020033:Protein Isoforms; D021122:Protein Subunits; D018091:Receptors, AMPA