RT Journal Article
SR Electronic
T1 Mutations within the Cholecystokinin-B/Gastrin Receptor Ligand ‘Pocket’ Interconvert the Functions of Nonpeptide Agonists and Antagonists
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 857
OP 863
DO 10.1124/mol.54.5.857
VO 54
IS 5
A1 Michael Bläker
A1 Yong Ren
A1 Michelle C. Gordon
A1 Jean E. Hsu
A1 Martin Beinborn
A1 Alan S. Kopin
YR 1998
UL http://molpharm.aspetjournals.org/content/54/5/857.abstract
AB 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.