A purified agonist-activated G-protein coupled receptor: truncated octopus Acid Metarhodopsin.

G-protein coupled receptors (GPCRs) mediate responses to many types of extracellular signals. So far, bovine rhodopsin, the inactive form of a GPCR, is the only member of the family whose three dimensional structure has been determined. It would be desirable to determine the structure of the active form of a GPCR.