Effects of net charge and the number of positively charged residues on the biological activity of amphipathic α‐helical cationic antimicrobial peptides

TLDR

Previous work used the 26‑residue amphipathic α‑helical peptide L‑V13K to probe how hydrophobicity influences its antimicrobial mechanism. This study examined how net charge and the number of positively charged residues on L‑V13K’s polar face affect its antimicrobial and hemolytic activities and biophysical properties. The authors synthesized V13K analogs with net charges from –5 to +10 and 1 to 10 positive residues, then measured MICs against six Pseudomonas aeruginosa strains and other bacteria, as well as the maximal non‑hemolytic concentration (MHC). Both net charge and positive residue count modulate antimicrobial and hemolytic activity, with a dramatic >32‑fold hemolysis increase when the polar face gains a single positive charge (from +8 to +9).

Abstract

In our previous study, we utilized a 26-residue amphipathic alpha-helical antimicrobial peptide L-V13K (Chen et al., Antimicrob Agents Chemother 2007, 51, 1398-1406) as the framework to study the effects of peptide hydrophobicity on the mechanism of its antimicrobial action. In this study, we explored the effects of net charge and the number of positively charged residues on the hydrophilic/polar face of L-V13K on its biological activity (antimicrobial and hemolytic) and biophysical properties (hydrophobicity, amphipathicity, helicity, and peptide self-association). The net charge of V13K analogs at pH 7 varied between -5 and +10 and the number of positively charged residues varied from 1 to 10. The minimal inhibitory concentrations (MIC) against six strains of Pseudomonas aeruginosa as well as other gram-negative and gram-positive bacteria were determined along with the maximal peptide concentration that produces no hemolysis of human red blood cells (MHC). Our results show that the number of positively charged residues on the polar face and net charge are both important for both antimicrobial activity and hemolytic activity. The most dramatic observation is the sharp transition of hemolytic activity on increasing one positive charge on the polar face of V13K i.e., the change from +8 to +9 resulted in greater than 32-fold increase in hemolytic activity (250 microg/ml to <7.8 microg/ml, respectively).