摘要
Initially,the Sigma-1 receptor(S1R)was incorrectly categorized as one of the opioid receptors.But it has since become clear that S1R is a non-opioid non-phencyclidine receptor with molecular chaperone activity.S1R is a 223 amino-acid long protein that shares no clear homology with any other known mammalian proteins,its closest homolog being the fungal ERG2 sterol isomerase.Even its pharmacological counterpart,the Sigma-2 receptor that was only recently cloned,is genetically distinct.S1R is more likely considered as an atypical ligand-modulated chaperone protein.S1R is widely expressed in many organs including brain where its function has mainly been explored.
