CONSERVED HIS(VI-17) OF THE NK-1 RECEPTOR IS INVOLVED IN BINDING OF NONPEPTIDE ANTAGONISTS BUT NOT SUBSTANCE-P

Residue number 17 in transmembrane segment VI has been shown to be cru cial for the binding of agonists in G-protein-coupled receptors for th e monoamines. In many peptide receptors a histidyl residue has been co nserved at this position. We find that replacement of His(VI-17) in th e NK-1 receptor with either glutamine, phenylalanine, or alanine has n o apparent effect on the binding of the natural peptide ligand substan ce P or on the agonist induced increase in inositolphosphate turnover. However, the binding of certain non-peptide antagonists was impaired; for example, replacement of His(VI-17) with alanine decreased the aff inity for FK888 and RP67,580 5- to 12-fold, respectively. A glutamine side chain was a good substitute for the imidazole in the binding of a ll non-peptide antagonists. It is concluded that the conserved His(VI- 17) in the NK-1 receptor is involved in the binding of certain non-pep tide antagonists, but is not important for the action of the natural p eptide agonist, substance P.