The function of GRM4 (glutamate metabotropic receptor 4, Ensembl gene identifier ENSG00000124493) is as follows. 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 inhibits adenylate cyclase activity. {ECO:0000269|PubMed:7617140, ECO:0000269|PubMed:8738157, ECO:0000269|PubMed:9473604}.