Purification of the antibacterial fragments of guinea-pig major basic protein.

In this study, we tried to purify the antibacterial fragments of guinea-pig major basic protein (MBP) using Staphylococcus aureus. The antibacterial activity of MBP was not affected by the pyridylethylation, suggesting that the disulfide bonds were not necessary for the antibacterial activity. When pyridylethylated-MBP was digested with alpha-chymotrypsin, the four potent antibacterial fragments (fragment V (Arg105-Tyr119), fragment IX (Thr1-Phe67), fragment X (Ile54-Leu97) and fragment XIII (Arg25-Phe67)) were isolated by reverse-phase high-performance liquid chromatography. Anti-MBP monoclonal antibody, BMK-13 neutralized the antibacterial activity of PE-MBP and fragments IX, X and XIII, but not the activity of fragment V, suggesting that Ile54-Phe67, the common amino-acid sequence of fragments IX, X and XIII, might be involved in the antibacterial activity of MBP. In fact, the synthetic peptide, Ile54-Phe67 exerted the antibacterial activity, and the activity was neutralized with BMK-13. The antibacterial activity of Ile54-Phe67 was lost by the modification with peptidylarginine deiminase which converted arginine residue to citrulline residue, suggesting that the arginine residues may be important for the antibacterial activity.