Importance of the C-terminal phenylalanine of gastrin for binding to the human CCK(2) receptor

• Published in: The journal of peptide research Vol. 58; no. 4; pp. 332 - 337
• Main Authors: Ahmed, S I, Wibowo, F, Gembitsky, D S, Bozsó, Z, Murphy, R F, Lovas, S
• Format: Journal Article
• Language: English
• Published: Denmark 01-10-2001
• Subjects: Amino Acid Motifs - physiology; Animals; Binding, Competitive - physiology; CHO Cells - metabolism; Cricetinae; Gastrins - chemistry; Gastrins - metabolism; Humans; Oligopeptides - chemical synthesis; Oligopeptides - metabolism; Phenylalanine - chemistry; Phenylalanine - metabolism; Protein Binding - physiology; Receptor, Cholecystokinin B; Receptors, Cholecystokinin - metabolism; Structure-Activity Relationship
• ISSN: 1397-002X

The importance of the C-terminal Phe of gastrin and structural requirements at position 17 for binding to the human CCK2 receptor were assessed using analogs of [Leu15]G(11-17). The following peptides were synthesized, Ac[Leu15]G(11-17), Ac[Leu15]G(11-16)NH2, [Leu15]G(11-17), [Leu15,Ala17]G(11-17), [Leu15,Abu17]G(11-17), [Leu15,Val17]G(11-17), [Leu15,Leu17]G(11-17), [Leu15,Cha17]G(11-17), [Leu15,Trp17]G(11-17), [Leu15,Tic17]G(11-17), [Leu15, d-Phe17]G(11-17) and [Leu15,p-X-Phe17]G(11-17), where X = F, Cl, Br, I, OH, CH3, NH2 and NO2. Competition binding experiments with [3H]CCK-8 were performed using human CCK2 receptors stably expressed in CHO cells. Phe17 was shown to be important for binding. A hydrophobic side-chain larger than Leu is required at position 17 but aromaticity does not appear to be essential. Constraint of the aromatic side-chain either in the g+ or g- conformation, as in the case of Tic, results in a significant decrease in affinity. In addition, the peptide conformation induced by incorporation of d-Phe decreases binding. The size and electron withdrawing/donating properties of the para substituent are not important for interaction with the receptor. The current study shows that the use of des-Phe analogs of gastrin is not a viable strategy for development of antagonists for the human CCK2 receptor.