Improving Conformational Stability and Bacterial Membrane Interactions of Antimicrobial Peptides with Amphipathic Helical Structure

Antimicrobial resistance (AMR) has become a massive concern because it causes the loss of human life and an economic burden in many parts of the world. Antimicrobial peptides (AMPs) can be investigated as an alternative solution to combat AMR because their mechanism has the potential to reduce microbe resistance. In this study, the native P01 peptide from Chondrus crispus macroalgae was modified to P01.1, P01.2, and P01.3 peptides via residue mutations and capping of the N- and C-termini to systematically improve their a-helical content, bacterial membrane interaction, and antibacterial activity. C-terminus amidation and mutations to remove helix breaker residues in P01 to give P01.1 peptide enhanced its a-helical stability. Acetylation of the N-terminus P01.1 to give P01.2 peptide further enhanced the a-helical content of the peptide. Mutations of low-to-high helical former residues in P01.2 to give P01.3 peptide further improve its a-helical stability. The binding activity of peptides to a model of Gram-positive membrane is in the following order P01.3 > P01.2 > P01.1 > P01; this is correlated with their antibacterial activity against Gram-positive S. aureus with MICs in the following order P01.3 = 15.63 mg/mL > P01.2 = 125 mg/mL > P01.1 and P01 larger than 250 mg/mL. In a model of Gram-negative membrane, the peptide-membrane binding is in the following order P01.3 = P01.2 > P01.1 > P01; however, P01.3, P01.2, and P01.1 have the same antibacterial activity against Gram-negative E.coli (MIC = 3.91 mg/mL) while P01 has no activity. In conclusion, the a-helical stability and amphipathicity of the peptide have correlation with the membrane binding and antibacterial activity of the peptide.