Mutational analysis of the putative devazepide binding site of the CCK-A receptor

Recently a molecular model was proposed for the binding site of the antagonist 3 S (−)- N -(2,3-dihydro-1-methyl-2-oxo-5-phenyl-1 H -1,4-benzodiazepine-3-yl)-1 H -indole-2-carboxamide (devazepide) on the cholecystokinin-A (CCK A ) receptor ( Van der Bent et al., 1994 . Drug Design Discov. 12, 129–148). Fifteen amino acids were identified, including hydrophilic ones such as Ser 139 , Asn 349 and Ser 379 , that might interact with the carboxamide moiety in devazepide. To provide mutational evidence for this model, wild-type and mutant receptors (S139A, N349A and S379A) were transiently expressed and compared with respect to the ability of devazepide to inhibit binding of radiolabelled cholecystokinin-(26–33)-peptide amide (CCK-8) and CCK-8-evoked Ca 2+ mobilization. The data presented suggest the involvement of the three residues in antagonist binding, although to a different extent. However, it does not seem likely that hydrogen bonds are the driving force in view of the relatively minor changes in receptor affinity and activity. © 1997 Elsevier Science B.V.