title: Oligomerization in the endoplasmic reticulum and intracellular trafficking of kainate receptors are subunit-dependent but not editing-dependent.
abstract: Investigating subunit assembly of ionotropic glutamate receptor complexes and their trafficking to the plasma membrane under physiological conditions in live cells has been challenging. By confocal imaging of fluorescently labeled kainate receptor (KAR) subunits combined with digital co-localization and fluorescence resonance energy (FRET) transfer analyses, we investigated the assembly of homomeric and heteromeric receptor complexes and identified the subcellular location of subunit interactions. Our data provide direct evidence for oligomerization of KAR subunits as early as following their biosynthesis in the endoplasmic reticulum (ER). These oligomeric assemblies pass through the Golgi apparatus en route to the plasma membrane. We show that the amino acid at the Q/R editing site of the KAR subunit GluR6 neither determines subunit oligomerization in the ER nor ER exit or plasma membrane expression, and that it does not alter GluR6 interaction with KA2. This finding sets KARs apart from alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptors, where in the absence of auxiliary proteins Q isoforms exit the ER much more efficiently than R isoforms. Furthermore, although KA2 subunits do not form functional homotetrameric complexes, we visualized their oligomerization (at least dimerization) in the ER. Finally, we demonstrate that plasma membrane expression of GluR6/KA2 heteromeric complexes is modulated not only by GluR6 but also KA2.
authors.affiliation: Department of Biochemistry I-Receptor Biochemistry, Ruhr University Bochum, Bochum, Germany.
authors.forename: Zhan-Lu
authors.initials: ZL
authors.lastname: Ma-Högemeier
authors.forename: Christoph
authors.initials: C
authors.lastname: Körber
authors.forename: Markus
authors.initials: M
authors.lastname: Werner
authors.forename: David
authors.initials: D
authors.lastname: Racine
authors.forename: Elke
authors.initials: E
authors.lastname: Muth-Köhne
authors.forename: Daniel
authors.initials: D
authors.lastname: Tapken
authors.forename: Michael
authors.initials: M
authors.lastname: Hollmann
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics; D002461:Cell Line, Transformed; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D031541:Fluorescence Resonance Energy Transfer / Q000379:methods; D005786:Gene Expression Regulation / Q000235:genetics; D006801:Humans; D008164:Luminescent Proteins / Q000235:genetics; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics; D018613:Microscopy, Confocal / Q000379:methods; D016297:Mutagenesis, Site-Directed; D018408:Patch-Clamp Techniques / Q000379:methods; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport / Q000502:physiology; D017393:RNA Editing / Q000502:physiology; D018092:Kainic Acid Receptors / Q000737:chemistry* / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D014162:Transfection / Q000379:methods
chemical_list: D001426:Bacterial Proteins; D008164:Luminescent Proteins; D021122:Protein Subunits; D018092:Kainic Acid Receptors; C054562:yellow fluorescent protein, Bacteria