Derive antibacterial peptides from hen egg lysozyme.

Hen egg white lysozyme is well known as a natural antimicrobial protein. It has attracted considerable interest as a natural preservative. However, its lytic activity is limited to certain Gram-positive bacteria. It is less effective against Gram-negative bacteria, including foodborne pathogens. There have been many attempts to modify the lytic activity of lysozyme using chemical or genetic engineering techniques.

Improving the spectrum of lysozyme activity is important for food and pharmaceutical applications. Scientists at Canada's University of Guelph have discovered new antibacterial peptides that result from the enzymatic hydrolysis of lysozyme. Their intention was to enhance the microbicidal activity of lysozyme and to study the structure-function relationships of antibacterial peptides. Their findings suggest there exist new opportunities for various lysozymes as novel natural antimicrobial agents. Hen egg white lysozyme contains unusual peptide sequences that can induce strong nonenzymatic microbicidal activity.

The investigators conducted the enzymatic hydrolysis of lysozyme using pepsin and trypsin. The molecular mass of the materials was analyzed. Antimicrobial assays were carried out using E. coli K12 and S. aureus. Lysozyme activity was determined by the lysis of cells of M. lysodeiktilus. Reverse-phase chromatography characterized the profile of antibacterial peptides derived from lysozyme.

Lysozyme was digested by pepsin to less than 5 kDa, while trypsin partially digested the lysozyme. Smaller peptides with less than 1 kDa were produced by the combination of both enzymes. Peptic digests of lysozyme completely lost enzyme activity, but they exhibited strong bactericidal activity against both Gram-negative and Gram-positive bacteria. Furthermore, smaller peptides released by pepsin and trypsin digests enhanced microbicidal activity.

Scanning electron microscopy indicated that the cell membranes of both bacteria were damaged by these peptides. These peptides probably have a different mechanism of action than native lysozyme. These results suggest that hen egg white lysozyme contains unusual peptide sequences that can induce strong nonenzymatic microbicidal activity that is released by enzyme hydrolysis.

Further information. Yoshinori Mine, Department of Food Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada; phone: [phone]; fax: [phone]; email: [e-mail].