CCK-B/gastrin receptor transmembrane domain mutations selectively alter synthetic agonist efficacy without affecting the activity of endogenous peptides

Citation
M. Blaker et al., CCK-B/gastrin receptor transmembrane domain mutations selectively alter synthetic agonist efficacy without affecting the activity of endogenous peptides, MOLEC PHARM, 58(2), 2000, pp. 399-406
Citations number
41
Categorie Soggetti
Pharmacology & Toxicology
Journal title
MOLECULAR PHARMACOLOGY
ISSN journal
0026895X → ACNP
Volume
58
Issue
2
Year of publication
2000
Pages
399 - 406
Database
ISI
SICI code
0026-895X(200008)58:2<399:CRTDMS>2.0.ZU;2-E
Abstract
Recent efforts have focused on identifying small nonpeptide molecules that can mimic the activity of endogenous peptide hormones. Understanding the mo lecular basis of ligand-induced receptor activation by these divergent clas ses of ligands should expedite the process of drug development. Using the c holecystokinin-B/gastrin receptor (CCK-BR) as a model system, we have recen tly shown that both affinity and efficacy of nonpeptide ligands are markedl y affected by amino acid alterations within a putative transmembrane domain (TMD) ligand pocket. In this report, we examine whether residues projectin g into the TMD pocket determine the pharmacologic properties of structurall y diverse CCK-BR ligands, including peptides and synthetic peptide-derived partial agonists (peptoids). Nineteen mutant human CCK-BRs, each including a single TMD amino acid substitution, were transiently expressed in COS-7 c ells and characterized. Binding affinities as well as ligand-induced inosit ol phosphate production at the mutant CCK-BRs were assessed for peptides (C CK-8 and CCK-4) and for peptoids (PD-135,158 and PD-136,450). Distinct as w ell as overlapping determinants of peptide and peptoid binding affinity wer e identified, supporting that both classes of ligands, at least in part, in teract with the CCK-BR TMD ligand pocket. Eight point mutations resulted in marked increases or decreases in the functional activity of the synthetic peptoid ligands. In contrast, the functional activity of both peptides, CCK -8 and CCK-4, was not affected by any of the CCK-BR mutations. These findin gs suggest that the mechanisms underlying activation of G-protein-coupled r eceptors by endogenous peptide hormones versus synthetic ligands may marked ly differ.