title: Importance of the C-terminal phenylalanine of gastrin for binding to the human CCK(2) receptor.
abstract: 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.
authors.affiliation: Department of Biomedical Sciences, Creighton University School of Medicine, 2500 California Plaza, Omaha, NE 68178, USA.
authors.forename: S I
authors.initials: SI
authors.lastname: Ahmed
authors.forename: F
authors.initials: F
authors.lastname: Wibowo
authors.forename: D S
authors.initials: DS
authors.lastname: Gembitsky
authors.forename: Z
authors.initials: Z
authors.lastname: Bozsó
authors.forename: R F
authors.initials: RF
authors.lastname: Murphy
authors.forename: S
authors.initials: S
authors.lastname: Lovas
mesh_terms: D020816:Amino Acid Motifs / Q000502:physiology; D000818:Animals; D001667:Binding, Competitive / Q000502:physiology; D016466:CHO Cells / Q000378:metabolism; D006224:Cricetinae; D005755:Gastrins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D009842:Oligopeptides / Q000138:chemical synthesis* / Q000378:metabolism; D010649:Phenylalanine / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding / Q000502:physiology; D043887:Receptor, Cholecystokinin B; D011949:Receptors, Cholecystokinin / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D005755:Gastrins; D009842:Oligopeptides; D043887:Receptor, Cholecystokinin B; D011949:Receptors, Cholecystokinin; D010649:Phenylalanine