Specific antimicrobial and hemolytic activities of 18-residue peptides derived from the amino terminal region of the toxin pardaxin.

Peptides are part of the host defense system against bacteria and fungi in species right across the evolutionary scale. However, endogenous antibacterial peptides are often composed of 25 residues or more and, therefore, are not ideal for therapeutic use. Hence it is of considerable interest to design and engineer short peptides having antimicrobial activity. Peptides composed of 18 amino acids, derived from the N-terminal region of the 33-residue toxin pardaxin (PX), GFFALIPKIISSPLFKTLLSAVGSALSSSGEQE, were synthesized and examined for biological activities. Peptide corresponding to the 1-18 stretch of PX exhibited antimicrobial activity only against Escherichia coli and not against Gram-positive microorganisms. The peptide also did not possess hemolytic activity. Replacement of P7 by A resulted in a peptide possessing both antibacterial and hemolytic activity. Substitution of both K residues by Q in the 'A' analog resulted in a peptide having only hemolytic activity. Conformational analysis of these peptides and investigation of their model membrane permeabilizing activities indicated that selective activity can be explained by their biophysical properties. Hence, by a rational design approach based on biophysical principles, it should be possible to generate short peptides having specific biological activity.