Title: Human kappa opiate receptor second extracellular loop elevates dynorphin's affinity for human mu/kappa chimeras
Abstract: To investigate roles of second extracellular loop sequences in peptide and nonpeptide ligand recognition by human opiate receptors, we have constructed a chimeric receptor in which this domain of the human p opiate receptor has been replaced with that of the human K opiate receptor.The chimeric opiate receptor displays dramatically increased affinity for dynorphin peptides.Affinities for dynorphin A-(1-17), dynorphin A-(1-131, and a-neoendorphin increase by up to 250-fold when compared with the wild-type human p opiate receptor.The chimera maintains recognition of the p-selective ligands morphine and [~-Ala~,MePhe',Gly-ol~Ienkephalin and displays no significant changes in affinity for the K-selective small molecule ligand U50,488.The chimeric opiate receptor displays evidence for effective G-protein coupling; 100 MI dynorphinA-(1-17) is as effective as 100 n~ morphine at inhibiting forskolin-stimulated adenyl cyclase activity through actions at the chimeric receptor.These data suggest that the putative second extracellular loop contributes substantially to the K receptor's selectivity in dynorphin ligand recognition.