|
The cannabinoid receptor type 2, abbreviated as CB2, is a G protein-coupled receptor from the cannabinoid receptor family that in humans is encoded by the ''CNR2'' gene.〔 It is closely related to the cannabinoid receptor type 1, which is largely responsible for the efficacy of endocannabinoid-mediated presynaptic-inhibition, the psychoactive properties of tetrahydrocannabinol, the active agent in marijuana, and other phytocannabinoids (natural cannabinoids). The principal endogenous ligand for the CB2 receptor is 2-arachidonoylglycerol (2-AG).〔 CB2 was cloned in 1993 by a research group from Cambridge looking for a second cannabinoid receptor that could explain the pharmacological properties of tetrahydrocannabinol.〔 The receptor was identified among cDNAs based on its similarity in amino-acid sequence to the cannabinoid receptor type 1 (CB1) receptor, discovered in 1990. The discovery of this receptor helped provide a molecular explanation for the established effects of cannabinoids on the immune system. == Structure == The CB2 receptor is encoded by the CNR2 gene. Approximately 360 amino acids comprise the human CB2 receptor, making it somewhat shorter than the 473-amino-acid-long CB1 receptor.〔 As is commonly seen in G protein-coupled receptors, the CB2 receptor has seven transmembrane spanning domains, a glycosylated N-terminus, and an intracellular C-terminus.〔 The C-terminus of CB2 receptors appears to play a critical role in the regulation of ligand-induced receptor desensitization and downregulation following repeated agonist application,〔 perhaps causing the receptor to become less responsive to particular ligands. The human CB1 and the CB2 receptors possess approximately 44% amino acid similarity.〔 When only the transmembrane regions of the receptors are considered, however, the amino acid similarity between the two receptor subtypes is approximately 68%.〔 The amino acid sequence of the CB2 receptor is less highly conserved across human and rodent species as compared to the amino acid sequence of the CB1 receptor. Based on computer modeling, ligand interactions with CB2 receptor residues S3.31 and F5.46 appears to determine differences between CB1 and CB2 receptor selectivity. In CB2 receptors, lipophilic groups interact with the F5.46 residue, allowing them to form a hydrogen bond with the S3.31 residue.〔 These interactions induce a conformational change in the receptor structure, which triggers the activation of various intracellular signaling pathways. Further research is needed to determine the exact molecular mechanisms of signaling pathway activation.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Cannabinoid receptor type 2」の詳細全文を読む スポンサード リンク
|