Interaction mode of calcium-binding peptides and Caco-2 cell membrane

In our previous studies, soluble soybean protein hydrolysate (SPH)-calcium complexes were shown to promote the calcium uptake of Caco-2 cells. However, the calcium transport mode involved remains unknown. In this article, several experiments were carried out via cytological analysis to investigate the calcium transport mode of peptides with low calcium binding capacities (F1), peptides with high calcium-binding capacities (F2), and their separate calcium complexes (F1-Ca and F2-Ca) when interacting with cell membranes. The interaction between one of them and a cell membrane is the first step in intracellular transport, as indicated by fluorescence blue shift experiments and acrylamide quenching experiments. The results of zeta potential experiments showed that only the "charge neutralization" phenomenon occurs when the F1 peptide or F1-Ca complex interacts with cell membranes and thus cannot be transported into cells. On the contrary, in an F2 at high concentrations or F2-Ca complex, a "charge recovery" phenomenon occurs apart from "charge neutralization" and can thus be transported into cells through endocytosis.