Characterization of the kainate-binding domain of the glutamate receptor GluR-6 subunit

• Published in: Biochemical journal 1998-03, Vol.330 ( Pt 3) (3), p.1461-1467
• Main Authors: Keinänen, K, Jouppila, A, Kuusinen, A
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Binding Sites; Binding, Competitive; Cell Membrane - metabolism; Cell Membrane - ultrastructure; Kinetics; Models, Molecular; Molecular Sequence Data; Peptide Fragments - biosynthesis; Peptide Fragments - chemistry; Peptide Fragments - metabolism; Protein Conformation; Radioligand Assay; Rats; Receptors, Glutamate - biosynthesis; Receptors, Glutamate - chemistry; Receptors, Glutamate - metabolism; Recombinant Proteins - biosynthesis; Recombinant Proteins - chemistry; Recombinant Proteins - metabolism; Spodoptera; Transfection
• ISSN: 0264-6021; 1470-8728
• DOI: 10.1042/bj3301461

Recombinant fragments of the kainate-selective glutamate recepto subunit GluR-6 were expressed in insect cells and analysed for [3H]kainate binding activity in order to characterize the structural determinants responsible for ligand recognition. Deletion of the N-terminal approximately 400 amino-acid-residue segment and the C-terminal approximately 90 residues resulted in a membrane-bound core fragment which displayed pharmacologically native-like [3H]kainate binding properties. Further replacement of the membrane-embedded segments M1-M3 by a hydrophilic linker peptide gave rise to a soluble polypeptide which was accumulated in the culture medium. When bound to chelating Sepharose beads via a C-terminal histidine tag, the soluble fragment showed low-affinity binding of [3H]kainate, which was displaced in a concentration-dependent manner by unlabelled domoic acid, L-glutamate and 6-cyano-7-nitroquinoxaline-2,3-dione. Our results indicate that the kainate-binding site is formed exclusively by the two discontinuous extracellular segments (S1 and S2) which are homologous to bacterial amino-acid-binding proteins. Ligand binding characteristics of soluble S1-S2 chimaeras between the GluR-6 and GluR-D subunits showed that, whereas both S1 and S2 segments contribute to agonist-selectivity, the N-terminal one-third of the GluR-D S2 segment is sufficient to confer alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate-binding capacity to the chimaeric ligand-binding domain.