Exploring the Calcium-Binding Mechanism of a Peptide KILDDTDNQ via Multispectral-Coupled Thermodynamic–Kinetic Analysis

The calcium-binding peptide KILDDTDNQ has been identified in phosvitin. This study aims to elucidate the absorption-transport characteristics, structural properties, and binding mechanism of the KILDDTDNQ-Ca complex. Stability analysis suggested that the KILDDTDNQ-Ca complex exhibited promising thermal, pH, and gastrointestinal stability, indicating exceptional processing performance. The calcium transport analysis based on Caco-2 cells showed that the KILDDTDNQ-Ca complex demonstrated 2-fold higher calcium absorption than inorganic calcium, reaching 30 μg/well. UV, XRD, and particle size analyses confirmed amorphous complex formation. Isothermal titration calorimetry revealed spontaneous 1:2 peptide-calcium binding. Molecular dynamics simulations showed that the coordination mode is bidentate, tridentate, or multidentate. The oxygen atoms of DDTD within the peptide KILDDTDNQ were mainly the binding sites of KILDDTDNQ with calcium. Hydrogen bonds, hydrophobic interactions, and electrostatic interactions stabilized the KILDDTDNQ-Ca complex. These results provide a theoretical reference and technical support for the development of novel calcium supplements.