GPCRs
Guanine nucleotide-binding protein-coupled receptors, also termed serpentine receptors, transduce signals from transmembrane receptors for sensory, hormonal, or photic stimuli into regulation of effector enzymes and ion channels. GPCRs are diverse and of ancient evolutionary lineage, and are found in fungi, plants, and animals. They share a common structure of plasma membrane-spanning helices with seven hydrophobic domains (7-TMSs). GPCRs are typically 20-28 amino acid residues long.
GPCRs are trimeric proteins that respond to a variety of specific ligands and stimuli – for example, photons, ions, biogenic amines, nucleosides, lipids, amino acids, and peptides. Transmembrane GPCRs bind GDP when inactive, and switch the bound nucleotide to GTP when activated.
The signalling cascade begins with attachment of a specific neurotransmitter ligand or a specific energetic stimulus, which initiates brief (seconds) binding of GTP rather than GDP. Signal transduction is accomplished through the coupling of G proteins to various secondary pathways involving ion channels, adenylyl cyclases, and phospholipases. Further, GPCRs may also couple to other proteins, such as those containing PDZ domains.
It is anticipated that future elucidation of GPCR constitution will reveal alpha-helical structures, consisting of 20 to 28 amino acids each.
On-line structural representations for the human µ opioid receptor, for example, is available as a 2D schematic. The 3D structure for inactive (dark) rhodopsin has been established, and the GPCRDB server holds atomic coordinates of 3D models of GPCRs. For more detailed information on-line about GPCRs, consult the GPCR database at GPCRDB.
The GPCRs have been divided into at least six families of GPCRs showing little to no sequence similarity.
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GPCRs are trimeric proteins that respond to a variety of specific ligands and stimuli – for example, photons, ions, biogenic amines, nucleosides, lipids, amino acids, and peptides. Transmembrane GPCRs bind GDP when inactive, and switch the bound nucleotide to GTP when activated.
The signalling cascade begins with attachment of a specific neurotransmitter ligand or a specific energetic stimulus, which initiates brief (seconds) binding of GTP rather than GDP. Signal transduction is accomplished through the coupling of G proteins to various secondary pathways involving ion channels, adenylyl cyclases, and phospholipases. Further, GPCRs may also couple to other proteins, such as those containing PDZ domains.
It is anticipated that future elucidation of GPCR constitution will reveal alpha-helical structures, consisting of 20 to 28 amino acids each.
On-line structural representations for the human µ opioid receptor, for example, is available as a 2D schematic. The 3D structure for inactive (dark) rhodopsin has been established, and the GPCRDB server holds atomic coordinates of 3D models of GPCRs. For more detailed information on-line about GPCRs, consult the GPCR database at GPCRDB.
The GPCRs have been divided into at least six families of GPCRs showing little to no sequence similarity.
Main page of BioChemistry : neurotransmitters : receptors : Main page of Molecule : neurotranmitter molecules : Main page of Pathways: Main page of Genes : Main page of Cell : energy transducers : Main page of Cell to Cell : neurotransmission : cellular signalling : Main page of Neuron : action potential : excitatory : inhibitory : metabotropic : synapse : Main page of Brain:
posted at 12/24/2006 11:18:00 PM
