Gausemycin Antibiotic Family Acts via Ca 2+ -Dependent Membrane Targeting.

We report the molecular mechanism of action of gausemycins and the isolation of new members of the family, gausemycins C ( 1c ), D ( 1d ), E ( 1e ), and F ( 1f ), the minor components of the mixture. To elucidate the mechanism of action of gausemycins, we investigated the antimicrobial activity of the most active compounds, gausemycins A and B, in the presence of Ca 2+ , other metal ions, and phosphate. Gausemycins require a significantly higher Ca 2+ concentration for maximum activity than daptomycin but lower than that required for malacidine and cadasides. Species-specific antimicrobial activity was found upon testing against a wide panel of Gram-positive bacteria. Membranoactivity of gausemycins was demonstrated upon their interactions with model lipid bilayers and micelles. The pore-forming ability was found to be dramatically dependent on the Ca 2+ concentration and the membrane lipid composition. An NMR study of gausemycin B in zwitterionic and anionic micelles suggested the putative structure of the gausemycin/membrane complex and revealed the binding of Ca 2+ by the macrocyclic domain of the antibiotic.