A comparative study was designed to evaluate the staphylococcidal efficiency of two sequence-related plasticins from the
dermaseptin superfamily we screened previously. Their
bactericidal activities against
Staphylococcus aureus as well as their
chemotactic potential were investigated. The impact of the GraS/GraR
two-component system involved in regulating resistance to
cationic antimicrobial peptides (CAMPs) was evaluated. Membrane disturbing activity was quantified by membrane
depolarization assays using the diS-C3 probe and by membrane integrity
assays measuring
beta-galactosidase activity with recombinant strain ST1065 reflecting compromised membranes and
cytoplasmic leakage. Interactions of plasticins with membrane models composed of either
zwitterionic lipids mimicking the
S. aureus membrane of CAMP-resistant strains or
anionic lipids mimicking the negative charge-depleted membrane of CAMP-sensitive strains were analyzed by jointed Brewster angle
microscopy (BAM),
polarization modulation
infrared reflection
absorption spectroscopy (PM-IRRAS), and
differential scanning calorimetry (DSC) to yield detailed information about the macroscopic interfacial organization, in situ conformation, orientation of the
peptides at the lipid-solvent interface, and lipid-phase disturbance. We clearly found evidence of distinct interfacial behaviors of plasticins we linked to the distribution of charges along the
peptides and structural interconversion properties at the membrane interface. Our results also suggest that
amidation might play a key role in GraS/GraR-mediated CAMP sensing at the
bacterial surface.
