Specific interaction between anionic phospholipids and milk bovine component PP3 and its 119–135 C-terminal fragment

Abstract

The behaviour of component PP3, a bovine milk protein with emulsifying properties, was investigated at the air–water interface and in a lipidic environment using the monolayer technique. The amphipathic 119–135 C-terminal fragment of PP3 was also tested since we proposed, on the basis of structural analysis, that this region is probably responsible for the surface-active properties of the protein. This hypothesis was confirmed by the tensiometric measurements at the air–water interface in which the addition of the C-terminal peptide increased the surface pressure with a similar amplitude as the whole protein. Penetration measurements into lipidic monolayers indicated that the insertion of component PP3 and its C-terminal peptide is the highest with anionic phospholipids in a gel state. Moreover, the electrostatic attractions provided by anionic phospholipids are essential for the peptide interaction. We also showed by Fourier transform infrared spectra study, that the peptide displays a β-type conformational state in aqueous solution and in the presence of solvant or anionic phospholipid (DPPG). In contrast, the protein adopts in aqueous solution an α helical conformation which remains the dominant conformational state in the presence of DPPG although the apparition of β-structure is detected.