Positive Charge Patterning and Hydrophobicity of Membrane-Active Antimicrobial Peptides as Determinants of Activity, Toxicity, and Pharmacokinetic Stability.

Natural α-helical cationic antimicrobial peptide (CAP) sequences are predominantly amphipathic, with only ca. 2% containing four or more consecutive positively charged amino acids (Lys/Arg). We have designed synthetic CAPs that deviate from these natural sequences, as typified by the charge-clustered peptide KKKKKKAAFAAWAAFAA-NH2, (termed 6K-F17), which displays high antimicrobial activity with no toxicity to mammalian cells. We created a series of peptides varying in charge patterning, increasing the amphipathic character of 6K-F17 to mimic the design of natural CAPs (e.g., KAAKKFAKAWAKAFAA-NH2). Amphipathic sequences displayed increased antimicrobial activity against bacteria but were significantly more toxic to mammalian cells and more susceptible to protease degradation than their corresponding charge-clustered variants, suggesting that amphipathic sequences may be desirable in nature to allow for more versatile functions (i.e., antibacterial, antifungal, antipredator) and rapid clearance from vulnerable host cells. Our approach to clustering of charges may therefore allow for specialization against bacteria, in concert with prolonged peptide half-life.