GPCR Bioassay

G Protein-Coupled Receptors (GPCRs) and G proteins (Guanine nucleotide-binding proteins) consist of three subunits: α, β, and γ, forming a heterotrimer. When an extracellular ligand binds to a GPCR, the G protein is activated, causing the Gα subunit to dissociate from the trimer and enter the cytoplasm, where it activates downstream effectors such as adenylyl cyclase (AC) or phospholipase C (PLC), thereby triggering biological effects. In addition, the β and γ subunits can also activate other pathways through proteins like phospholipase A2, producing biological effects. Typically, the term “G protein” refers to the α subunit.

The GPCR superfamily comprises 600–1,000 proteins and represents the largest class of molecular targets with therapeutic potential known to date. In current drug discovery, 40% of screening efforts are directed toward GPCRs, and more than 50% of marketed drugs exert their effects through GPCRs. GPCRs have thus become the primary target class in drug screening.