IDENTIFICATION AND ISOLATION OF A BACTERICIDAL DOMAIN IN CHICKEN EGG-WHITE LYSOZYME

Chicken egg white lysozyme exhibits antimicrobial activity against bot h Gram-positive and Gram-negative bacteria. Fractionation of clostripa in-digested lysozyme yielded a pentadecapeptide with antimicrobial act ivity but without muramidase activity. The peptide was isolated and it s sequence found to be I-V-S-D-G-N-G-M-N-A-W-V-A-W-R (amino acids 98-1 12 of chicken egg white lysozyme). A synthesized peptide of identical sequence had the same bactericidal activity as the natural peptide, Re placement of Trp 108 with tyrosine significantly reduced the antibacte rial capacity of the peptide. By replacement of Trp 111 with tyrosine the antibacterial activity was lost. Replacement of Asn 106 with the p ositively charged arginine strongly increased the antibacterial capaci ty of I-V-S-D-G-N-G-M-N-A-W-V-A-W-R. The peptide I-V-S-D-G-N-G-M consi sting of the eight amino acids of the N-terminal side had no bacterici dal properties, whereas the peptide N-A-W-V-A-W-R of the C-terminal si de retained some bactericidal activity. Replacement of asparagine 106 by arginine (R-A-W-V-A-W-R) increased the bactericidal activity consid erably. The D enantiomer of R-X-W-V-A-W-R was as active as the L form against five of the tested bacteria, but substantially less active aga inst Serratia marcescens, Micrococcus luteus, Staphylococcus aureus, S taphylococcus epidermidis and Staphylococcus lentus. For these bacteri al species some stereospecific complementarity between receptor struct ures of the bacteria and the peptide can be assumed.