Structural determinants of the immunomodulatory properties of the C-terminal region of bovine β-casein

Bovine β-casein and its C-terminal sequence (191-209) were previously shown to possess immunomodulatory properties in studies on partially purified peptides from hydrolysates, where minor amounts of contaminants may affect the cellular response. The inhibitory effect of β-casein and of eight C-terminus synthetic β-casein peptides on mitogen-induced spleen cell proliferation was compared. Use of synthetic peptides allowed the unambiguous and accurate identification that a seven amino acid sequence at the C-terminus, including a PFP motif, was sufficient for immunomodulation. Substitution of the last proline (P206) in the PFP motif with D-Pro had a negative impact on the immunosuppressory activity of all these short peptides, whereas substitution of P206 with structural analogues of proline had almost no impact. A relationship was found between the immunomodulatory properties and the structural features of these peptides, as assessed by various spectroscopic approaches, indicating a role of structure in eliciting the immunomodulatory activity of these peptides.