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Novel antibacterial peptides derived from hen egg lysozyme |
Y. MINE1, S. Lauriau, and F. Ma1. (1) Dept. of Food Science, Univ. of Guelph, Guelph, ON N1G2W1, Canada Hen egg white lysozyme (muramidase, EC 3.2.1.17) is well known as a natural antimicrobial protein and has been attracted considerable interest as a natural food preservative. However, its lytic activity is limited to certain Gram-positive bacteria, and less effective against to Gram-negative bacteria including food borne pathogens. Many attempts to modify lytic activity of lysozyme by chemical or genetic engineering have been documented in the past decade. Improving the spectrum of lysozyme activity is important for food and pharmaceutical applications. We have discovered new antibacterial peptides from enzymatic hydrolysis of lysozyme. Our objective was to enhance microbicidal activity of lysozyme and to study structure-function relationships of antibacterial peptides. Enzymatic hydrolysis of lysozyme was conducted using pepsin and trypsin. Molecular mass of the digests was analyzed by Tri-trichine SDS-PAGE. Antimicrobial assays were carried out using Escherichia coli K12 and Staphylococcus aureus. Lysozyme activity was determined by the lysis of M. lysodeiktilus cells. Reverse-phase HPLC column was used to characterize the profile of antibacterial peptides derived from lysozyme. Lysozyme was digested by pepsin to less 5 kDa, while trypsin partially digested. Smaller peptides with less 1 kDa were produced by the combination of both enzymes. Peptic digests of lysozyme completely lost enzyme activity, but exhibited strong bactericidal activity against both Gram-negative and -positive bacteria. Furthermore, smaller peptides released by pepsin and trypsin digests enhanced microbicidal activity. Scanning electron microscopy clearly demonstrated that cell membrane of both bacteria was damaged by these peptides. Thus, these peptides probably have a different mechanism of action than native lysozyme. These results suggest that hen egg white lysozyme contains unique peptide sequences which can induce strong non-enzymatic microbicidal activity and released by enzyme hydrolysis. These findings open up new opportunities for various lysozyme applications as novel natural antimicrobial agents.
Session 11, Food Chemistry: Proteins
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