Binding of cholecystokinin-8 (CCK-8) peptide derivatives to CCKA and CCKB receptors

The structural requirements for the selective binding of cholecystokinin-8 (CCK-8)-related peptides to peripheral (CCKA) receptors are not sufficiently understood. In this study, the interaction of a series of newly shortened analogues of CCK-8 with both receptor subtypes was analyzed by displacement studies using [3H]-CCK-8 and 125I-Bolton-Hunter (BH)-CCK-8 as radioligands. The pentapeptide derivative of CCK-8, succinyl-Tyr (SO3H)-Met-Gly-Trp-Met-phenethylamide, was found to bind selectively with high affinity to the CCKA receptor. The replacement of Met28 and/or Met31 by norleucine and of L-Trp30 by its D-analogue had no significant effect on the binding properties of the peptide. Further C-terminal shortening resulted in a drastic loss of affinity and selectivity of the CCK receptor binding.