Modulation of Antimicrobial Activities of Aib-Based Artificial Amphipathic α-Helical Peptides by Incorporating Histidine Residues.

Cationic antimicrobial peptides (CAMPs) exhibit potent antibacterial activity by disrupting bacterial membranes. We investigated the effect of histidine incorporation on BKBA-20, a designed amphiphilic helical peptide composed of alternating 2-aminoisobutyric acid (Aib) and lysine. Substitution at lysine sites (1a-1e series) reduced net charge and antimicrobial activity, though certain analogues (1c, 1d) demonstrated minimal antibacterial activity against Escherichia coli. In contrast, substitution at Aib sites (2a-2c series) preserved some extent of helical structure and improved activity under acidic conditions. Notably, substitutions at the terminal of the peptide were more effective at acidic pH, while the slightly medial side of the peptide favored activity at neutral pH. Hemolysis assays confirmed low cytotoxicity of the modified peptides. These results suggest histidine incorporation as a promising strategy to broaden the spectrum of CAMPs, particularly against Gram-negative bacteria, without increasing toxicity.