Interaction of alpha s2- and beta-casein signal peptides with DMPC and DMPG liposomes

Interactions of casein signal peptides (CSP) and derivatives were detected with dimyristoylphosphatidyl-glycerol and -choline liposomes. Fluorescence anisotrophy indicated that the peptides interact better with DMPG than DMPC, inserting at a limited depth in the bilayer. Stronger interaction was detected for derivatives of beta-CSP than of alpha s2-CSP. Tryptophan fluorescence (intrinsic, energy transfer, quenching) showed that the central hydrophobic core of CSP was buried in the bilayer whereas both ends remained outside, adopting a hairpin-like conformation. The secondary structure of the CSP was not affected by their interactions with phospholipids. beta-CSP derivatives show both lytic and fusogenic activities.