Scientists tweaked a small piece of the natural antimicrobial protein LL‑37 called GF‑17 by swapping some amino acids for lysine. Changing lysine on the “hydrophobic” side made the peptide much better at killing microbes while being far less harmful to human cells, especially in a version named GF17‑8, which was about 25 times safer than the original.

GF-17, the main antimicrobial domain of LL-37, exhibits optimal amphipathicity and heightened hydrophobicity, leading to increased hemolytic activity. A series of novel GF-17-like antimicrobial peptides (AMPs) were designed using lysine scanning to explore how lysine substitutions at various positions impact the biological activity of GF-17. The results showed that lysine substitutions increased the overall charge of GF-17 while decreasing its overall hydrophobicity. Lysine substitution occur at the hydrophilic surface of the GF-17 α-helix increase the peptide drophobic moment, slightly affect its antimicrobial and hemolytic activity. However, when the lysine substitution occue at the hydrophobic surface of the GF-17, the biological activity of GF-17 changes differs. The results indicate that the position of positively charged lysine residue affects the biophysical properties and selectivity of the peptide. Moreover, GF17-8 was a peptide with high antimicrobial activity and low toxicity in vivo and in vitro. GF17-8 exhibited a potent geometric mean MIC of 7.18 μM and a dramatically improved therapeutic index (27.86), thereby representing a 25-fold enhancement over GF-17, due to lysine substitution on its hydrophobic face. These findings offer valuable insights for designing and optimizing antimicrobial peptides beneficial for developing future antimicrobial agents.