The Lasso Peptide Siamycin-I Targets Lipid II at the Gram-Positive Cell Surface

Abstract

Ribosomally synthesized post-translationally modified peptides (RiPPs) are a diverse class of biologically active molecules produced by many environmental bacteria. While thousands of these compounds have been identified, mostly through genome mining, a relatively small number has been investigated at the molecular level. One less understood class of RiPPs is the lasso peptides. These are 20−25 amino acid residue compounds bearing an N-terminal macrocyclic ring and a Cterminal tail that is threaded through the ring. We have carried out a detailed investigation on the mechanism of action of the siamycin-I lasso peptide. We demonstrate that siamycin-I interacts with lipid II, the central building block of the major cell wall component peptidoglycan, which is readily accessible on the outside of the cell. This interaction compromises cell wall biosynthesis in a manner that activates the liaI stress response. Additionally, resistance to siamycin-I can be brought about by mutations in the essential WalKR two-component system that causes thickening of the cell wall. Siamycin-I is the first lasso peptide that has been shown to inhibit cell wall biosynthesis.

Ca2+-Daptomycin targets cell wall biosynthesis by forming a tripartite complex with undecaprenyl-coupled intermediates and membrane lipids

“…Luciferase reporter assays. B. subtilis luciferase reporter assays were conducted as previously described 60 . Briefly, strains were grown in Mueller-Hinton broth at 30°C containing 5 µg ml −1 chloramphenicol until they reached an OD 600 of 0.5.…”

Identification and Heterologous Expression of the Biosynthetic Gene Cluster Encoding the Lasso Peptide Humidimycin, a Caspofungin Activity Potentiator

“…Two disulfide bonds containing linkages Cys1  Cys13 and Cys7  Cys19 form the tricyclic structure [22]. Recently, Tan et al [27] have found that siamycin I binds and inhibits the action of lipid II, the essential precursor molecule involved in peptidoglycan formation. Given the few differences in the amino acid sequences of class I lasso peptides, it might be also expected that other molecules of this group, including humidimycin, also inhibit peptidoglycan biosynthesis [27].…”

Put a Bow on It: Knotted Antibiotics Take Center Stage

“…Importantly, only eight antibacterial lasso peptides have been connected to a cellular or molecular target; in most cases, the mechanisms of action remain obscure. Of the compounds that have been studied to date, the three main targets are RNA polymerase, ClpC 1 of the ClpC 1 P 1 P 2 protease complex and lipid II, the key precursor molecule of peptidoglycan [35,58,59] (Figure 5).…”

“…It was shown to activate the lia (lipid II-interfering antibiotics) operon, suggesting that it might impair peptidoglycan biosynthesis. A detailed analysis into siamycin-I’s target and mechanism of action was further pursued where it was found to bind and inhibit the action of lipid II, the essential precursor molecule involved in peptidoglycan formation [59].…”