Hairpin structure stability plays a role in the activity of two antimicrobial peptides

Many naturally occurring antimicrobial peptides (AMPs) are amphipathic with a β-hairpin conformation stabilized by cross-strand disulfides across the associated β-strands. Here, we show that the disulfides are not essential. Other structuring means such as better β-turns and noncovalent cross-strand interactions can, with proper design, replace the disulfides with no loss in antimicrobial activity. Our results also demonstrate that the hairpin turn region may play a role in membrane recognition for at least one member of this class, since a homodimeric turnless β-sheet analog showed no antimicrobial activity. We also examined the effects of N-terminal fatty acid adducts on AMPs. Surprisingly, the large hydrophobic carboxylic moieties examined completely eliminated the antimicrobial activity of previously active β-hairpin peptides.