Modulation of calcium chelation and intestinal transport by acidic residue arrangement in cod bone-derived peptides: Insights from sequence redesign and quantum chemical analysis.

Acidic residues are widely recognized as key structural motifs for calcium coordination in calcium-chelating peptides, yet how their spatial arrangement modulates calcium chelation and intestinal transport remains poorly defined. In this study, LTVEDKD and GPDGEEGK were selected from cod bone hydrolysate based on their structural characteristics, and two derivatives, GPDGEGEK and GPAGAAGK, were rationally designed to evaluate the roles of acidic-residue presence and arrangement. Calcium-chelating capacity followed the order LTVEDKD > GPDGEEGK > GPDGEGEK > GPAGAAGK, indicating that the presence and local arrangement of acidic residues are crucial determinants of calcium chelation. UV-Vis, FT-IR, Raman spectroscopy, and quantum chemical calculations revealed that carboxyl and amide groups served as major coordination sites, while electrostatic attraction and coordination bonds contributed to the stabilization of peptide-calcium chelates. Caco-2 cell assays demonstrated that stronger calcium chelation promoted calcium uptake and transepithelial transport. These findings provide mechanistic insights for designing peptide-based calcium delivery systems.