Interaction of the 47-residue antibacterial peptide seminalplasmin and its 13-residue fragment which has antibacterial and hemolytic activities with model membranes.

The interaction of seminalplasmin (SPLN), a 47-residue antibacterial peptide, and its 13-residue fragment (SPF), which has antibacterial and hemolytic activities, with model membranes has been investigated. The fluorescence characteristics of the single Trp residue in these peptides indicate strong binding to lipid vesicles. SPLN binds more strongly to dioleoylphosphatidylglycerol vesicles compared to dioleoylphosphatidylcholine and phosphatidylserine vesicles. Localization studies using fluorescence quenchers like NO3-, I-, and acrylamide indicate that the Trp residues in both of the peptides are located away from the head group region and are associated with the hydrophobic core. Both peptides cause release of carboxyfluorescein from zwitterionic as well as anionic vesicles. The biological activities of SPLN and SPF have been rationalized in terms of lipid-peptide interactions. It is proposed that the specificity in biological activity arises due to differences in the manner in which the peptides associate with the bacterial and red blood cell surfaces.