G-protein coupled receptor for glutamate. Ligand binding causes a conformation change that triggers signaling via guanine nucleotide-binding proteins (G proteins) and modulates the activity of down-stream effectors. Signaling activates a phosphatidylinositol-calcium second messenger system. May participate in the central action of glutamate in the CNS, such as long-term potentiation in the hippocampus and long-term depression in the cerebellum (PubMed:10945991, PubMed:1438218, PubMed:1656524, PubMed:1847995). May function in the light response in the retina (By similarity). Homodimer; disulfide-linked (PubMed:11069170, PubMed:11867751). The PPXXF motif binds HOMER1, HOMER2 and HOMER3. Interacts with TAMALIN (PubMed:11850456). Interacts with RYR1, RYR2, ITPR1, SHANK1 and SHANK3. Interacts with SIAH1 (PubMed:10469171). Predominantly expressed in cerebellar Purkinje cells, CA2-CA3 pyramidal cells of the hippocampus, and mitral and tufted cells of the olfactory bulb. Activated by quisqualate > glutamate > ibotenate > trans-1- aminocyclopentyl-1,3-dicarboxylate; inhibited by 2-amino-3-phosphonopropionate. C-terminally truncated forms of isoform 1A. C-terminally truncated forms of isoform 1A. Belongs to the G-protein coupled receptor 3 family.