1H NMR conformational study of sulfated and non-sulfated cholecystokinin fragment CCK27-33: influence of the sulfate group on the peptide folding.

1H NMR study of cholecystokinin fragment (CCK27-33) in (C2H3)2SO and in 2H2O at different pH shows that sulfated (CCK7) and non sulfated (NS-CCK7) peptides are under preferentially folded conformations characterized by a beta-turn including the sequence Gly-Trp-Met-Asp with a H-bond between the CO of Gly and the NH of Asp. This structure is probably stabilized by an ionic interaction between Tyr and Asp. Moreover, the N-terminal part of CCK7 forms a C7 structure with a weak H-bond between the CO of Gly and the NH of Trp. In this model all CCK7 hydrophobic side chains are in close vicinity, far from the hydrophilic sulfate group. Full interaction with brain CCK8 receptors could require both the sulfate group and the maintaining of conformational constraints.