A truncated nisin variant, lipidated at its C-terminus, displays improved stability and increased antibacterial activity against methicillin-resistant Staphylococcus aureus

Abstract

The rise of bacterial resistance has prompted researchers to shift their focus toward alternative antimicrobial agents, including antimicrobial peptides (AMPs). Some naturally occurring AMPs are lipidated, showing similarity with clinically used antimicrobial agents such as daptomycin and polymyxins, which are lipidated peptides. In this study, we investigate the impact of various lipid modifications on nisin. Nisin is a well-studied 34-amino acid AMP, ribosomally synthesized and post-translational modified, which is effective against many Gram-positive bacteria and is widely used as a food preservative. Wild-type nisin and two truncated forms, nisin(1–31) and nisin(1–20) were conjugated at the C-terminus with either a C4, C6, C8, or C10 lipid tail. Antimicrobial activity was assessed against two Gram-positive strains: methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus faecium (VRE). Our results show that the lipidation of wild-type nisin and nisin(1–31) reduced its antibacterial activity, with the longest chains exhibiting the lowest inhibitory effects. However, lipidation of the nisin fragment nisin(1–20), especially with C8 resulting in compound 12, enhanced its antibacterial activity and specificity against S. aureus species, making it four times more potent than wild-type nisin. Mode-of-action studies revealed that the lipidated construct 12 retained its ability to bind lipid II but does not induce pore formation in S. aureus. Notably, due to its short length, ring-protected structure, and lipid modification, the construct demonstrated improved proteolytic stability against chymotrypsin, trypsin and protease K. Our findings suggest that optimizing lipid–peptide combinations can lead to more effective, specific, and stable candidates for antimicrobial development.