TY - JOUR T1 - Mutations within the Cholecystokinin-B/Gastrin Receptor Ligand ‘Pocket’ Interconvert the Functions of Nonpeptide Agonists and Antagonists JF - Molecular Pharmacology JO - Mol Pharmacol SP - 857 LP - 863 DO - 10.1124/mol.54.5.857 VL - 54 IS - 5 AU - Michael Bläker AU - Yong Ren AU - Michelle C. Gordon AU - Jean E. Hsu AU - Martin Beinborn AU - Alan S. Kopin Y1 - 1998/11/01 UR - http://molpharm.aspetjournals.org/content/54/5/857.abstract N2 - We have reported previously that the transmembrane domains of the cholecystokinin-B/gastrin receptor (CCK-BR) comprise a putative ligand binding pocket. In the present study, we examined whether amino acid substitutions within the CCK-BR pocket altered the affinities and/or functional activities of L-365,260 (the prototypical nonpeptide CCK-BR antagonist) and two structural derivatives, YM022 (a higher affinity antagonist) and L-740,093S (a partial agonist). Eight amino acids that project into the CCK-BR pocket were individually replaced by alanine, using site-directed mutagenesis. Affinities for the nonpeptide molecules, as well as ligand-induced inositol phosphate production, were assessed with the wild-type and mutant receptors. For each of the nonpeptide ligands examined, a distinct series of mutations altered the affinity, suggesting that each ligand possessed a characteristic pattern of interactions within the CCK-BR pocket. Basal signaling levels and inositol phosphate formation induced by the full agonist CCK octapeptide were comparable for the wild-type receptor and all of the mutant CCK-BR forms. In contrast to the peptide agonist CCK octapeptide, the functional activities of the nonpeptide molecules were selectively altered by single point mutations within the CCK-BR pocket, resulting in interconversion of agonists and antagonists. These findings suggest that interactions between nonpeptide molecules and transmembrane domain amino acids of the CCK-BR can determine the functional activity and affinity of the ligands. ER -