Conformational and molecular modeling studies of sulfated cholecystokinin-15

Abstract Conformational features of the C-terminal carboxyamidated pentadecapeptide of CCK (S 19 HRISDRD[SO 4 ]–YMGWMDF 33 –NH 2 ) were determined by NMR spectroscopy in a zwitterionic membrane-mimetic solvent system, composed of DPC micelles. The C-terminal octapeptide consisted of a well-defined pseudohelix that was nearly identical to the structure previously reported for nonsulfated CCK-8 in the same solvent system. N-terminal amino acids of CCK-15 were highly disordered, with no clear conformational preference. Extensive NOE-restrained molecular dynamics simulations of the CCK-15/CCK 1 –R complex suggested that almost all the experimentally determined intermolecular contact points provided by NMR, site-directed mutagenesis, and photoaffinity labeling could be simultaneously satisfied, when the N-terminus of the ligand is placed in close spatial proximity to the N-terminus of the receptor.