G protein-coupled receptor (GPCR)

A G protein-coupled receptor is a cell-surface protein that senses a signal outside the cell and relays it inward through G proteins.

GPCRs form the largest family of receptors in the human body and are the target of a large share of prescription drugs. Each one threads through the cell membrane seven times, with a binding pocket facing outward and a G protein docking site facing inward. When a ligand binds, the receptor changes shape, activates its G protein, and sets off second messengers such as cyclic AMP or calcium that change what the cell does.

Readers of cannabinoid science meet GPCRs constantly, because the two classical cannabinoid receptors, CB1 and CB2, are GPCRs, as are GPR55, GPR18 and the serotonin 1A receptor. Whether a compound acts as an agonist, antagonist, inverse agonist or allosteric modulator describes how it changes a GPCR's signaling. Cannabidiol's interactions with several GPCRs have been studied mostly in laboratory models, and how those findings translate to people is still being worked out.