G-protein coupled receptor for 5-hydroxytryptamine (serotonin) (PubMed:1330647, PubMed:18703043, PubMed:19057895). Also functions as a receptor for various drugs and psychoactive substances, including mescaline, psilocybin, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and lysergic acid diethylamide (LSD) (PubMed:28129538). Ligand binding causes a conformation change that triggers signaling via guanine nucleotide-binding proteins (G proteins) and modulates the activity of down-stream effectors (PubMed:28129538). Beta-arrestin family members inhibit signaling via G proteins and mediate activation of alternative signaling pathways (PubMed:28129538). Signaling activates phospholipase C and a phosphatidylinositol-calcium second messenger system that modulates the activity of phosphatidylinositol 3-kinase and promotes the release of Ca(2+) ions from intracellular stores (PubMed:18703043, PubMed:28129538). Affects neural activity, perception, cognition and mood (PubMed:18297054). Plays a role in the regulation of behavior, including responses to anxiogenic situations and psychoactive substances. Plays a role in intestinal smooth muscle contraction, and may play a role in arterial vasoconstriction. (Microbial infection) Acts as a receptor for human JC polyomavirus/JCPyV. Interacts (via C-terminus) with MPDZ and PATJ (PubMed:11150294, PubMed:14988405). May interact (via C-terminus) with MPP3, PRDX6, DLG4, DLG1, CASK, APBA1 and MAGI2 (PubMed:14988405). Interacts with GRM2 and DRD2; this may affect signaling (PubMed:18297054, PubMed:21645528, PubMed:22300836). Detected in brain cortex (at protein level). Detected in blood platelets. The PDZ domain-binding motif is involved in the interaction with PATJ, CASK, APBA1, DLG1 and DLG4. Binds lysergic acid diethylamine (LSD) in the orthosteric pocket (Probable). Bound LSD dissociates extremely slowly, with a residence time of about 221 minutes at 37 degrees Celsius. Belongs to the G-protein coupled receptor 1 family. The Singapore human mutation and polymorphism database