A large number of
antimicrobial peptides depend on intramolecular
disulfide bonds for their biological activity. However, the relative
instability of disulfide bonds has limited the potential of some of
these peptides to be developed into therapeutics. Conversely, peptides
containing intramolecular (methyl)lanthionine-based bonds, lanthipeptides,
are highly stable under a broader range of biological and physical
conditions. Here, the class-II lanthipeptide synthetase CinM, from
the cinnamycin gene cluster, was employed to create methyllanthionine
stabilized analogues of disulfide-bond-containing antimicrobial peptides.
The resulting analogues were subsequently modified
in vitro
by adding lipid tails of variable lengths through chemical addition.
Finally, the created compounds were characterized by MIC tests against
several relevant pathogens, killing assays, membrane permeability
assays, and hemolysis assays. It was found that CinM could successfully
install methyllanthionine bonds at the intended positions of the analogues
and that the lipidated macrocyclic core peptides have bactericidal
activity against tested Gram-positive and Gram-negative pathogenic
bacteria. Additionally, fluorescence microscopy assays revealed that
the lipidated compounds disrupt the bacterial membrane and lyse bacterial
cells, hinting toward a potential mode of action. Notably, the semisynthesized
macrocyclic lipo-lanthipeptides show low hemolytic activity. These
results show that the methods developed here extend the toolbox for
novel antimicrobial development and might enable the further development
of novel compounds with killing activity against relevant pathogenic
bacteria.