G protein-coupled receptor

A cell-surface receptor that activates intracellular heterotrimeric G proteins when specific signals bind. Its seven membrane-spanning segments enable it to transmit signals across the cell membrane.

Heterotrimeric G protein: A signaling complex of one alpha, one beta, and one gamma subunit that relays signals from activated receptors. The receptor activates this membrane-associated complex by promoting nucleotide exchange on its alpha subunit.
Seven-transmembrane domain: A protein architecture in which seven alpha helices cross a membrane and form a ligand-responsive receptor core. This shared structural feature defines the characteristic GPCR fold.
Adrenergic receptor: A GPCR activated by adrenaline or noradrenaline that regulates responses including heart activity and smooth-muscle tone. This receptor family illustrates how GPCR signaling shapes physiology and drug treatment.
Receptor tyrosine kinase: A cell-surface receptor that activates its own or associated tyrosine kinase activity after ligand binding. It transmits signals through phosphorylation rather than activating heterotrimeric G proteins.
Brian Kobilka: An American physician-scientist whose structural studies clarified how G protein-coupled receptors activate. His work helped reveal the activated structure of a GPCR bound to its G protein.
G protein cycle: The sequence of GDP and GTP binding and hydrolysis that switches heterotrimeric G proteins between inactive and active states. Receptor-catalyzed GDP release starts the cycle that separates signaling subunits.
Ligand: A molecule or ion that binds selectively to a protein, often changing its activity. Hormones, neurotransmitters, odorants, and other signals bind GPCRs as ligands.
Muscarinic acetylcholine receptor: A GPCR activated by acetylcholine that mediates diverse effects in the nervous system and peripheral organs. Its subtypes show how one neurotransmitter can produce distinct GPCR-mediated responses.
Ligand-gated ion channel: A membrane protein that opens an ion-conducting pore when a ligand binds. Unlike GPCRs, it can convert ligand binding directly into ion flow across the membrane.
Robert Lefkowitz: An American physician-scientist who established key principles of GPCR binding, regulation, and signaling. His research helped define how these receptors respond to hormones and undergo desensitization.

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