G protein-coupled receptors (GPCRs) - Edubirdie

University:
University of California, San Diego
Course:
BIMM 100 | Molecular Biology
Academic year:

2024
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241

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1
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customer-8930767

mechanism of action of G protein-coupled receptors (GPCRs) from ligand binding to second messenger generation, using the ?-adrenergic receptor as a model. GPCRs are seven-transmembrane domain receptors that transduce extracellular signals via heterotrimeric G proteins (G???). The ?-adrenergic receptor (?-AR) binds epinephrine/norepinephrine, activating G? (stimulatory G protein). Inactive G? binds GDP and associates with G??. Ligand binding to ?-AR induces conformational change, exposing the G protein-binding site. The activated receptor acts as a guanine nucleotide exchange factor (GEF), promoting GDP release from G?. GTP binding (GTP > GDP intracellularly) dissociates G?-GTP from G?? and the receptor. Both G?-GTP and free G?? can signal. G?s-GTP activates adenylyl cyclase (AC), converting ATP to cAMP (second messenger). cAMP activates protein kinase A (PKA), which phosphorylates targets (e.g., phosphorylase kinase, CREB, ion channels), leading to increased heart rate, glycogen breakdown, and gene transcription. Termination: G? hydrolyzes GTP to GDP (aided by RGS proteins), reassociating with G??. ?-AR is phosphorylated by GRK (G protein-coupled receptor kinase) and binds ?-arrestin, causing desensitization and internalization. Other GPCRs use different G proteins: G? inhibits AC (reducing cAMP); G? activates phospholipase C?, generating IP? (Ca²? release) and DAG (PKC activation). Over 800 human GPCRs are drug targets (e.g., ?-blockers, antihistamines). Mutations cause diseases (e.g., retinitis pigmentosa, thyroid adenomas). GPCR signaling exemplifies amplification: one ligand ? many activated G proteins ? many cAMP ? many PKA ? thousands of phosphorylated targets.

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