Structure-function study of helical antimicrobial peptides

Abstract

Parasin I, a 19-aa antimicrobial peptide isolated from the catfish skin, shows potent antimicrobial activity against a broad spectrum of pathogens. Therefore, to elucidate the structural features that are required for its potent antimicrobial activity and to produce parasin I analogs with increased activity, we studied the relationship between the structure and the activity of parasin I and investigated the mechanism of action of parasin I. The structure of parasin I, determined by nuclear magnetic resonance analysis, consisted of an alpha-helical region (residues 9-17) flanked by random coil regions (residues 1-8 and 18-19). To elucidate the structure-activity relationship of parasin I, we synthesized a series of N- and C-terminally truncated or amino acid-substituted synthetic parasin I analogs and examined their antimicrobial activity. Deletion of the lysine residue at the N-terminal abolished the antimicrobial activity whereas the deletion of the C-terminal random coil region slightly increased the antimicrobial potency of the peptide. Progressive deletions at the C-terminal did not cause substantial changes in antimicrobial activity of the resulting peptides until five residues were truncated whereupon the antimicrobial activity was almost completely destroyed. Regardless of helical content, a basic residue at the N-terminal was necessary for the peptides to bind to Escherichia coli cell membranes. Among the membrane-binding peptides, only those peptides with helical structure were able to permeabilize the cell membranes. Our results suggest that the lysine residue at the N-terminal mediates the binding of parasin I to the cell membrane while the helical structure of parasin I is responsible for the membrane permeabilizing activity, which kills the microorganism. A systematic approach to overcome the salt-sensitivity of parasin I was designed by the application of helix-capping motifs. The effect of helix-capping motifs on salt-sensitive antimicrobial pept...