Identification of a second membrane-active 13-residue peptide segment in the antimicrobial protein, bovine seminalplasmin.

Seminalplasmin (SPLN) is a 47-residue protein from bovine seminalplasma having broad-spectrum antibacterial activity. The protein has no hemolytic activity. SPLN interacts with lipid vesicles and its antibacterial activity appears to stem from its ability to permeabilize the bacterial plasma membrane. Analysis of SPLN's primary structure, with respect to its relative hydrophobicity and hydrophilicity, revealed a segment, PKLLETFLSKWIG, more hydrophobic than the rest of the protein. A synthetic peptide corresponding to this region had not only antibacterial activity but also hemolytic properties. Analysis of the SPLN sequence based on hydrophobic moment plots has revealed a second segment, SLSRYAKLANRLA, which could be membrane active. A synthetic peptide corresponding to this region shows only antibacterial activity with no hemolytic activity.