Differential Features of Cholecystokinin-Releasing Peptides Derived from Food Proteins: Peptide Length, Amino Acid Composition and Primary Structure; Analysis of Currently Identified Peptide Sequences

The mouse enteroendocrine cell line STC-1 has been widely used to investigate the effects of dietary protein-derived peptides on cholecystokinin (CCK) secretion. The studies have also addressed the question of whether specific structural features of a given peptide chain may be related to higher secretagogue activity with respect to others, but a detailed structure–activity relationship in CCK-releasing peptides has not yet been reported. The aim of this study was to list the currently available CCK-releasing peptide sequences; to draw conclusions about the role played by peptide length, peptide amino acid composition and peptide amino acid sequence in differentiating their secretagogue activity; and to highlight the physicochemical properties and sequence motifs shared by the active peptides, and any possible differential feature between CCK-releasing peptides and ineffective peptides. To this end, a method was applied consisting of the fractionation of peptide sets into subsets and the comparison between paired subsets of active and inactive peptides. A few distinctive structural features related to CCK-releasing activity were highlighted for each subset. Actually, minor changes in the primary structure can make the difference between active and inactive peptides, as suggested by previous studies. Hence, the chance of predicting the activity of a peptide that has never been tested in vitro using reference structures must still be considered to be low.