Synthetic Lugdunin Analogues Reveal Essential Structural Motifs for Antimicrobial Action and Proton Translocation Capability

Abstract

Lugdunin, a novel thiazolidine cyclopeptide, exhibits micromolar activity against methicillin‐resistant Staphylococcus aureus (MRSA). For structure–activity relationship (SAR) studies, synthetic analogues obtained from alanine and stereo scanning as well as peptides with modified thiazolidine rings were tested for antimicrobial activity. The thiazolidine ring and the alternating d ‐ and l ‐amino acid backbone are essential. Notably, the non‐natural enantiomer displays equal activity, thus indicating the absence of a chiral target. The antibacterial activity strongly correlates with dissipation of the membrane potential in S. aureus. Lugdunin equalizes pH gradients in artificial membrane vesicles, thereby maintaining membrane integrity, which demonstrates that proton translocation is the mode of action (MoA). The incorporation of extra tryptophan or propargyl moieties further expands the diversity of this class of thiazolidine cyclopeptides.

Secretion of and Self-Resistance to the Novel Fibupeptide Antimicrobial Lugdunin by Distinct ABC Transporters in Staphylococcus lugdunensis

“…Lugdunin, the first non-ribosomally synthesized antibiotic from human microbiomes, has a novel structure and an unusual protonophore-like mode of action, which distinguishes it from most of the antibiotics in clinical use (9). Lugdunin causes proton leakage in synthetic, protein-free membrane vesicles, suggesting that it does not need to target a proteinaceous molecule to exert its antibacterial activity (9). The atypical mode of action on November 6, 2020 by guest http://aac.asm.org/ Downloaded from raised the question whether the bacterial producer strains would also use an unusual mechanism to achieve self-resistance to lugdunin.…”

“…The plates were incubated for 48 h under continuous shaking in a microplate reader and OD was measured every minutes.Synthetic lugdunin congeners and control compounds. All synthetic lugdunin derivatives were synthesized as described elsewhere(9). Daptomycin (Cubicin) was purchased from MSD Sharp & Dohme GmbH (Haar, Germany), CCCP, gramicidin S and nigericin were obtained from SigmaAldrich (now Merck, Germany).…”

Bacterial pathogens: threat or treat (a review on bioactive natural products from bacterial pathogens)

“…29 This ve-membered thiazolidine resembles a clasp that "adorns" the peptide backbone, hence the term bupeptides was coined for this new class of compounds (Latin bula, meaning clasp). 175 The biosynthetic mechanism for lugdunin production features several unusual aspects of the domains and their overall organization (Fig. 12).…”

“…179 SAR studies indicate that the cyclic structure of the peptide, the N-unsubstituted thiazolidine "clasp", two amino acids tryptophan and leucine, and an alternating D-and L-amino acid backbone are integral to the activity. 175 The nonpolar tryptophan and leucine residues interact with the hydrophobic regions of the bacterial cell membranes similar to the activity of poly-(Trp-Leu)-octapeptides. 180 Fibupeptides like lugdunin carry electronically charged particles across the membrane and consequently disintegrate the membrane potential, thereby killing the bacteria.…”

“…Incorporation of an additional tryptophan motif in the peptide backbone intensies this membrane interaction and further strengthens the antibacterial effect, exhibiting two-fold increased activity over the parent compound. 175 Lugdunin or analogues thereof are promising candidates for the treatment of multi-drug resistant Grampositive infections. However, it may be challenging to develop these into systemic therapeutics considering that they are membrane-targeting antibiotics.…”