Conformational and molecular modeling studies of beta-cyclodextrin-heptagastrin and the third extracellular loop of the cholecystokinin 2 receptor

The conformational features of a conjugate of the C-terminus of human gastrin (HG[11−17]), the shortest gastrin sequence retaining biological function, with β-cyclodextrin ([Nle15]-HG[11−17]−βCD) were determined by NMR spectroscopy in an aqueous solution of dodecylphosphocholine (DPC) micelles. The peptide−βCD conjugate displays a binding affinity and activation profile comparable to those of HG[11−17] at the cholecysokinin 2 (CCK2) receptor, the G protein-coupled receptor responsible for the gastrointestinal function of gastrin. The structure of the peptide consisted of a well-defined β-turn between Gly13 and Asp16 of gastrin. The structural preferences of [Nle15]-HG[11−17]−βCD in DPC micelles and the 5-doxylstearate-induced relaxation of the 1H NMR resonances support a membrane-associated receptor recognition mechanism. Addition of [Nle15]-HG[11−17]−βCD to the third extracellular loop domain of the CCK2 receptor, CCK2-R(352−379), generated a number of intermolecular nuclear Overhauser enhancements (NOEs...