Calcium Binding Mechanism of Soybean Peptide with Histidine Alteration by Molecular Docking Analysis and Spectroscopic Methods

Histidine (His) carries a unique heteroaromatic imidazole side chain and plays an irreplaceable role in peptides and proteins. With the current study, we aimed to determine the characteristics and functional activities of the bone density of soy peptide–calcium complexes in which a His residue was replaced by Leu (CBP-H). Soybean peptide (CBP-H) was chemically synthesized, the binding mechanism between CBP-H and calcium ions in combination was determined with bioinformatics and spectroscopy analysis, and the difference between CBP and CBP-H was investigated. Finally, we analyzed the effect of CBP and CBP-H on osteoblasts in vitro. The results showed that CBP-H could bind to calcium ions, and the calcium coordinated with the carboxyl groups of Asp and Glu in the peptide. The nitrogen atoms of the amino group and the oxygen atoms of the carboxyl group in CBP-H significantly contributed to the coordination with Ca(2+). Furthermore, the binding capacity was 36.48 ± 0.09 mg/g, similar to CBP. However, both CBP and CBP-H could promote osteogenic activity, the activity of CBP-H was 127.147%, lower than CBP (121.777%). While it had the same ability to promote intracellular calcium concentration, CBP-H could upregulate 150.12% calcium ions into the intracellular, and the rate of the rise of CBP was 158.91%, further highlighting the potential of His residues for binding calcium and treating osteoporosis.