Towards the design of hypolipidaemic peptides: Deoxycholate binding affinity of hydrophobic peptide aggregates of casein plastein

Plastein is a thixotropic product of protease-induced peptide aggregation. This study evaluated the effects of the modified peptide structure of plastein on its affinity for a secondary bile acid. Casein plastein formation resulted in decreased free amino nitrogen and increased mean particle size, surface hydrophobicity and hydrophobic-to-hydrophilic amino acid ratio of the peptides. The net negative surface charge of casein hydrolysate (CH) was decreased (P < 0.05) in crude plastein (CPc) and completely lost in the isolated plastein (CPi) resulting in the formation of insoluble aggregates. The surface and structural changes in CPi were associated with 38.5 ± 0.0% binding of physiological level of sodium deoxycholate, higher (P < 0.05) than the activities of CPc (23.1 ± 0.0%) and CH (12.8 ± 4.4%). Maximum specific ligand binding (Bmax) was higher (P < 0.05) for CPc (0.391 ± 0.021 mM/mg protein) than CH (0.246 ± 0.043 mM/mg protein) and CPi (0.234 ± 0.005 mM/mg protein). However, CPi had the strongest affinity for sodium deoxycholate with the lowest dissociation constant (Kd) of 2.719 ± 0.146 mM, which was 2.5- and 3-folds lower (P < 0.05) than those of CH and CPc, respectively. Understanding deoxycholate-binding affinity of peptides can facilitate the design of potent food-based BA sequestrants for managing hypercholesterolaemia (dyslipidaemia) and associated health conditions.