Structure of Cholecystokinin Receptor Binding Sites and Mechanism of Activation/Inactivation by Agonists/Antagonists

Abstract

Delineation of CCK receptor binding sites is a prerequisite for the understanding of the molecular basis for ligand recognition, partial agonism, ligand-induced traffiking of receptor signalling. In the current paper, we illustrate how, in the past 5 years, studies from our laboratory and others have provided new data on the molecular basis of the pharmacology and functioning of CCK1 and CCK2 receptors. Available data on CCK1 and CCK2R binding sites indicate that 1) homologous regions of the two receptors are involved in the binding site of CCK, however, positioning of CCK slightly differs; 2) binding sites of non-peptide agonists/ antagonist are buried in the pocket formed by transmembrane helices and overlap that of CCK and 3) residues of the binding sites as well as of conserved motifs such as E/DRY, NPXXY are crucial for receptor activation.The actions of cholecystokinin (CCK) and gastrin are mediated by specific high affinity membrane receptors on target cells. These receptors have been characterized pharmacologically and biologically and are divided into two subtypes based on their affinities for CCK and gastrin. The CCK1 receptor (previously named CCK-A receptor) has an approximately 500 times higher affinity for CCK than for gastrin and the CCK2 receptor (previously named CCKB/ G receptor) has the same high affinity for both CCK and gastrin. An additional difference between the CCK1 and CCK2 receptors resides in their affinities for sulfated and non-sulfated CCK. Indeed, whereas the CCK1 receptor binds and responds to sulfated CCK with 500 times higher affinity/potency than non-sulfated CCK, the CCK2 receptor weakly discriminates between the two (Silvente-Poirot et al. 1993;Wank 1998).

Conformational Analysis of Invariant Peptide Sequences in Bacterial Genomes

“…It is known that buried residues, which are expected to contribute more to the thermodynamic stability, are usually more conserved than surface residues. 16,17 This has also been experimentally demonstrated, for example, in the case of cholecystokinin receptor, 18 ARM and HEAT protein repeats, 19 bacterial multidrug transporters, 20 etc.…”

Gastrin, cholecystokinin and gastrointestinal tract functions in mammals

“…These two subtypes of receptors were previously called CCK-A and CCK-B (or CCK-B/gastrin), respectively, and they were renamed CCK 1 and CCK 2 receptors following the International Union of Pharmacology Committee on Receptor Nomenclature and Drug Classification (Vanhoutte et al 1996;Noble et al 1999). The main characteristics of these two major subtypes of CCK and gastrin receptors known until now have been well described along with the transduction mechanisms responsible for their message translation (Wank, 1995;Yassin, 1999;Fourmy et al 2002;Miyasaka & Funakoshi, 2003).…”

Conformationally Constrained CCK8 Analogues Obtained from a Rationally Designed Peptide Library as Ligands for Cholecystokinin Type B Receptor

“…The that there is no exchange between different peptide conformers during a slow NMR timescale. The iterative comparison of NOESY, COSY, and TOCSY spectra according to the sequencespecific method [18] allowed us to unambiguously assign almost all 1 H NMR signals (but no stereospecific assignments have been attempted, see Table 2). The analysis of a NOESY spectrum acquired at 298 K, with a mixing time of 150 ms, allowed us to obtain a total of 193 geometric constraints, amongst which 72 were inter-residue nonsequential (however, 18 of these 72 constraints involve residues Glu 28/Lys 32, whose side chains are covalently linked to close the cyclic moiety).…”

“…[1] CCK A -R and CCK B -R are membrane bound receptors belonging to the superfamily of G-protein-coupled receptors (GPCRs) and are predominantly located in the gastrointestinal tract and the central nervous system, respectively. Many efforts have been put into developing selective CCK analogues with either agonist or antagonist activity.…”