Bactericidal activity of human lysozymes carrying various lengths of polyproline chain at the C-terminus

The amphiphilic polypeptide polyproline having different chain lengths was connected to the C-terminus of human lysozyme by the recombinant DNA technique. The hydrophobicity of human lysozyme increased with increasing length of the polyproline chain. Although the bactericidal activity of wild-type lysozyme is limited to gram-positive bacteria and the hydrolytic activity of the mutant lysozyme decreased with increasing chain length of polyproline, the mutant lysozymes showed bactericidal activity to gram-negative bacteria and the activity increased with increasing hydrophobicity of the mutant enzyme. Experiments with Escherichia coli phospholipid liposomes revealed that the mutant human lysozymes dissipated the valinomycin-induced transmembrane electrochemical potential, and the dissipation increased with increasing hydrophobicity. The increased hydrophobicity of the mutant enzyme may induce interaction of lysozyme with the outer membrane and subsequent penetration into the inner membrane of E. coli, resulting in an increase of bactericidal activity.