The orphan glutamate-like receptor GluR␦2 is predominantly expressed in Purkinje cells of the central nervous system. The classification of GluR␦2 to the ionotropic glutamate receptor family is based on sequence similarities, because GluR␦2 does not form functional homomeric glutamate-gated ion channels in transfected cells. Studies in GluR␦2 ؊/؊ knockout mice as well as in mice with naturally occurring mutations in the GluR␦2 gene have demonstrated an essential role of GluR␦2 in cerebellar long-term depression, motor learning, motor coordination, and synaptogenesis. However, the lack of a known agonist has hampered investigations on the function of GluR␦2. In this study, the ligand-binding core of GluR␦2 (GluR␦2-S1S2) was found to bind neutral amino acids such as D-serine and glycine, as demonstrated by isothermal titration calorimetry. Direct evidence for binding of D-serine and structural rearrangements in the binding cleft of GluR␦2-S1S2 is provided by x-ray structures of GluR␦2-S1S2 in its apo form and in complex with D-serine. Functionally, D-serine and glycine were shown to inactivate spontaneous ion-channel conductance in GluR␦2 containing the lurcher mutation (EC 50 values, 182 and 507 M, respectively). These data demonstrate that the GluR␦2 ligand-binding core is capable of binding ligands and that cleft closure of the ligandbinding core can induce conformational changes that alter ion permeation.crystal structure ͉ electrophysiology ͉ isothermal titration calorimetry ͉ ligand-binding core

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A comparison of the pharmacological and physiological properties of the metabotropic glutamate 1 alpha and 1 beta receptors (mGluR1 alpha and mGluR1 beta) expressed in baby hamster kidney (BHK 570) cells was performed. The mGluR1 beta receptor is an alternatively spliced form of mGluR1 alpha with a modified carboxy terminus. Immunoblots of membranes from the two cell lines probed with receptor-specific antipeptide antibodies showed that mGluR1 alpha migrated with an M(r) = 154,000, whereas mGluR1 beta migrated with an M(r) = 96,000. Immunofluorescence imaging of receptors expressed in BHK 570 cells revealed that the mGluR1 alpha receptor was localized to patches along the plasmalemma and on intracellular membranes surrounding the nucleus, whereas mGluR1 beta was distributed diffusely throughout the cell. Agonist activation of the mGluR1 alpha and the mGluR1 beta receptors stimulated phosphoinositide hydrolysis. At both receptors, glutamate, quisqualate, and ibotenate were full agonists, whereas trans-(+)-1-aminocyclopentane-1,3-dicarboxylate appeared to act as a partial agonist. The stimulation of phosphoinositide hydrolysis by mGluR1 alpha showed pertussis toxin-sensitive and insensitive components, whereas the mGluR1 beta response displayed only the toxin-insensitive component. The mGluR1 alpha and mGluR1 beta receptors also increased intracellular calcium levels by inducing release from intracellular stores. These results indicate that the different carboxy terminal sequences of the two receptors directly influences G protein coupling and subcellular deposition of the receptor polypeptides and suggest that the two receptors may subserve different roles in the nervous system.

The G-protein-coupled metabotropic glutamate receptor mGluRla and the ionotropic glutamate receptor GluR6 were examined for posttranslational palmitoylation. Recombinant receptors were expressed in baculovirusinfected insect cells or in human embryonic kidney cells and were metabolically labeled with [3HI palmitic acid. The metabotropic mGluRla receptor was not labeled whereas the GluR6 kainate receptor was labeled after incubation with Receptors for the excitatory neurotransmitter L-glutamate can be grouped into two major families, ionotropic receptors and metabotropic receptors. The metabotropic glutamate receptors are G-protein-linked receptors coupled to effectors such as phospholipase C and adenylyl cyclase, whereas the ionotropic receptors form homomeric and heteromeric ligandgated ion channels permeable to mono-and divalent cations. A further subdivision of the ionotropic family can be made on the basis of agonist selectivity, giving the a-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) (GluR1-4, also called GluRA-D), kainate (GluR5-7, KA-1, KA-2), and Nmethyl-D-aspartate (NMDA) classes of receptors (1).Several studies have examined various aspects of the structure and function of the GluR6 kainate receptor (2-10). The activity of GluR6 channels can be modulated by protein kinase A (6, 7) and protein kinase C (PKC) (8). Site-directed mutagenesis of asparagine-linked glycosylation sites (9-12) and epitope tagging studies (13) have been carried out to derive transmembrane topological models of kainate and AMPA receptors. In these models, a large extracellular aminoterminal domain is followed by either three or five transmembrane domains (TMDs), resulting in either case in a carboxyl terminus that is intracellular.Palmitoylation is a posttranslational modification whereby a C16 fatty acyl chain is covalently bound to a nascent protein in a post-endoplasmic reticulum or pre-Golgi compartment. The fatty acid can be attached to a serine, threonine, or cysteineThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. residue via an ester or thioester bond. In contrast to myristoylation, which occurs cotranslationally and without metabolic turnover (14), a rapid, dynamic turnover of palmitate has been demonstrated in several systems (15)(16)(17).Several G-protein-linked receptors, including rhodopsin (18) and 132-adrenergic (19)