Contemporary medicine has been confronted by multidrug resistance. Therefore, new antibiotics are sought to alleviate the problem. In this study, we estimated the effect of the positioning and extent of lipidation (mainly octanoic acid residue) in the KR12-NH2 molecule on antibacterial and hemolytic activities. The effect of the conjugation of benzoic acid derivatives (C6H5-X-COOH, where X: CH2, CH2-CH2, CH=CH, C≡C, and CH2-CH2-CH2) with the N-terminal part of KR12-NH2 on biological activity was also studied. All analogs were tested against planktonic cells of ESKAPE bacteria and reference strains of Staphylococcus aureus. The effect of lipidation site on the helicity of the KR12-NH2 analogs was studied using CD spectroscopy. The ability of the selected peptides to induce the aggregation of POPG liposomes was evaluated with DLS measurements. We demonstrated that both the site and extent of peptide lipidation play an essential role in the bacterial specificity of the lipopeptides. Most of the C8α-KR12-NH2 (II) analogs that were more hydrophobic than the parent compound were also more hemolytic. A similar relationship was also found between the α-helical structure content in POPC and hemolytic activity. It is worth emphasizing that in our study, the highest selectivity against S. aureus strains with an SI value of at least 21.11 exhibited peptide XII obtained by the conjugation of the octanoic acid with the N-terminus of retro-KR12-NH2. All lipidated analogs with the highest net charge (+5) were the most selective toward pathogens. Therefore, the overall charge of KR12-NH2 analogs plays pivotal role in their biological activity.
Keywords: CD spectroscopy; ESKAPE pathogens; KR12; LL37; Staphylococcus aureus; dynamic light scattering; lipopeptide.