Background: In the last years, Antimicrobial Peptides (AMPs) and lipopeptides have received attention as promising candidates to treat infections caused by resistant microorganisms.
Objective: The main objective of this study was to investigate the effect of repetitive KLFK motifs and the attachment of aliphatic acids to the N-terminus of (KLFK)n peptides on therapeutic properties.
Methods: Minimal inhibitory concentration against Gram (+) and (-) bacteria and yeast of synthetic compounds were determined by broth microtiter dilution method, and the toxicity was evaluated by hemolysis assay. Membrane-peptide interaction studies were performed with model phospholipid membranes mimicking those of bacterial and mammalian cells by Fluorescence Spectroscopy. The secondary structure in solution and membranes was determined by Circular Dichroism.
Results: Our results showed that the resulting compounds have inhibitory activity against bacteria and fungi. The (KLFK)3 peptide showed the highest therapeutic index against bacterial and yeast strains, and the (KLFK)2 peptide conjugated with octanoic acid was the most active against yeasts. All the lipopeptides containing long-chain fatty acids (C14 or longer) were highly hemolytic at low concentrations. The antimicrobial activity of (KLFK)2 and (KLFK)3 lipopeptides was mainly associated with improved stability of the amphipathic secondary structure, which showed high contributions of α-helix in dipalmitoylphosphatidylglycerol (DPPG) vesicles.
Conclusion: The repetition of the KLFK sequence and the conjugation with lipid tails allowed obtained compounds with high antimicrobial activity and low toxicity, becoming good candidates for treating infectious diseases.
Keywords: Peptide; antimicrobial activity; critical micelle concentration; fluorescence spectroscopy; hemolytic activity; lipopeptides; secondary structure..
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