Transducer Mechanisme: G Protein–Gekoppelde Receptoren

G protein–coupled receptors, or GPCRs, constitute the most prominent family of cell surface receptors and are targeted by nearly 35% of approved drugs.

Although there are multiple subtypes of GPCRs, they share common structural features.

All GPCRs contain seven transmembrane α-helices separated by alternating cytosolic loops that contain the binding site for heterotrimeric G proteins. The three extracellular loops together form the ligand-binding site.

Ligand binding induces a conformational change in the GPCR. The activated GPCR can now bind the inactive GDP-bound G protein with increased affinity to form a receptor-G protein complex.

Receptor-G protein interaction further induces conformational changes in the G protein, triggering the exchange of GDP with GTP.

Next, the GTP-bound subunit of the G protein dissociates from the GPCR and activates downstream effectors.

Ligands such as neurotransmitters, opioids, hormones, or cytokines bind different GPCRs that activate various G-α subtypes to regulate neurotransmission, visual perception, and immune response.