title: Night blindness-associated mutations in the ligand-binding, cysteine-rich, and intracellular domains of the metabotropic glutamate receptor 6 abolish protein trafficking.
abstract: Mutations in the GRM6 gene, which encodes the metabotropic glutamate receptor 6 (mGluR6), lead to autosomal recessive congenital stationary night blindness (CSNB), which is characterized by loss of night vision due to a defect in signal transmission from photoreceptor to the adjacent ON-bipolar cells in the retina. So far, the sequence variations that have been described in six different families include nonsense, frameshift, and missense mutations. Here we investigated the impact of missense mutations in the ligand-binding domain, a conserved cysteine-rich domain, and the intracellular domain on the localization of the protein. We visualized and discriminated between surface and intracellular protein. Here we demonstrate that the wild-type (wt) protein localizes to the cell surface, and to endoplasmic reticulum (ER) and Golgi compartments. This also holds true for a mGluR6 variant containing a polymorphic, nondisease-associated amino acid exchange in the ligand-binding domain. In contrast, all disease-associated missense mutations lead to retention of the protein in the ER, while dimerization seems not to be affected. This is the first report that shows that CSNB-associated mutations in three different domains of mGluR6 abolish proper protein trafficking. We propose that the ligand-binding and the poorly characterized cysteine-rich domains, in addition to the intracellular domains, have a pivotal role in correct trafficking of metabotropic glutamate receptors to the cell surface.
authors.affiliation: Institute of Medical Genetics, Division of Medical Molecular Genetics and Gene Diagnostics, University of Zurich, Zurich, Switzerland. zeitz@medgen.unizh.ch
authors.forename: Christina
authors.initials: C
authors.lastname: Zeitz
authors.forename: Ursula
authors.initials: U
authors.lastname: Forster
authors.forename: John
authors.initials: J
authors.lastname: Neidhardt
authors.forename: Silke
authors.initials: S
authors.lastname: Feil
authors.forename: Stefan
authors.initials: S
authors.lastname: Kälin
authors.forename: Dorothee
authors.initials: D
authors.lastname: Leifert
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Flor
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Berger
mesh_terms: D000818:Animals; D019556:COS Cells; D002460:Cell Line; D002522:Chlorocebus aethiops; D019295:Computational Biology; D003545:Cysteine / Q000378:metabolism*; D019281:Dimerization; D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D050505:Mutant Proteins / Q000378:metabolism; D020125:Mutation, Missense / Q000235:genetics*; D009755:Night Blindness / Q000235:genetics*; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D051381:Rats; D018094:Receptors, Metabotropic Glutamate / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism
chemical_list: D008024:Ligands; D050505:Mutant Proteins; D018094:Receptors, Metabotropic Glutamate; D011993:Recombinant Fusion Proteins; C113897:metabotropic glutamate receptor 6; D003545:Cysteine