opioid receptor binding

Definition

Target type: molecularfunction

Binding to an opioid receptor. [GOC:nln]

Opioid receptors are a class of G protein-coupled receptors (GPCRs) that are activated by opioid ligands, such as morphine, heroin, and endorphins. Opioid receptor binding initiates a signaling cascade that leads to a variety of cellular responses, including analgesia, euphoria, respiratory depression, and constipation. The molecular function of opioid receptor binding involves the following steps: 1) Binding of an opioid ligand to the receptor. Opioid ligands bind to the receptor's transmembrane domain, which is composed of seven alpha helices. This binding event causes a conformational change in the receptor, which activates its intracellular signaling pathways. 2) Activation of G proteins. The activated opioid receptor interacts with a heterotrimeric G protein, which is composed of alpha, beta, and gamma subunits. The alpha subunit of the G protein binds to GTP (guanosine triphosphate), which causes it to dissociate from the beta and gamma subunits. 3) Activation of downstream signaling pathways. The activated alpha subunit of the G protein can then activate a variety of downstream signaling pathways, including the adenylate cyclase pathway, the mitogen-activated protein kinase (MAPK) pathway, and the phospholipase C pathway. These pathways are responsible for mediating the physiological effects of opioid receptor activation. 4) Desensitization of the receptor. Prolonged exposure to opioid ligands can lead to desensitization of the receptor, which is a process in which the receptor becomes less responsive to further stimulation. Desensitization is thought to be caused by phosphorylation of the receptor by G protein-coupled receptor kinases (GRKs). Phosphorylation of the receptor can lead to its internalization, which removes it from the cell surface. 5) Termination of signaling. The signaling cascade initiated by opioid receptor binding is eventually terminated by the hydrolysis of GTP to GDP (guanosine diphosphate) by the alpha subunit of the G protein. This hydrolysis event causes the alpha subunit to reassociate with the beta and gamma subunits, which inactivates the G protein and terminates the signaling cascade.'
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Proteins (2)

Compounds (6)