Seventransmembrane

Seventransmembrane refers to proteins that traverse the lipid bilayer seven times, forming seven transmembrane α-helices. The best-known class is G protein-coupled receptors (GPCRs), a large and diverse family that mediates response to photons, hormones, neurotransmitters, and environmental stimuli. GPCRs typically have an extracellular N-terminus, seven hydrophobic transmembrane helices (TM1–TM7) connected by three extracellular loops and three intracellular loops, and an intracellular C-terminus. The ligand binding site is usually within the transmembrane core or at the extracellular face, and ligand-induced conformational changes in the helices enable coupling to heterotrimeric G proteins or β-arrestins on the cytoplasmic side to trigger intracellular signaling cascades.

GPCRs are targets for a large fraction of therapeutic drugs, reflecting their central role in physiology and pharmacology. Other seven-transmembrane proteins exist, including some bacterial sensors, but GPCRs are the predominant eukaryotic examples. Structural insights from X-ray crystallography and cryo-electron microscopy have revealed the canonical seven-helix bundle and ligand binding pockets, as well as the conformational changes associated with activation. GPCRs typically range from about 300 to 500 amino acids in length and are encoded by a large gene family across animals and other kingdoms.

The seven-transmembrane architecture is a defining feature of this receptor class, underpinning a wide array of signaling modalities and serving as a major focal point in drug discovery and basic biology. Examples include rhodopsin, beta-adrenergic receptors, serotonin receptors, dopamine receptors, and odorant receptors.