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Δευτέρα 15 Οκτωβρίου 2018

Daptomycin pore formation and stoichiometry depends on membrane potential of target membrane [Mechanisms of Action]

Daptomycin is a calcium-dependent lipodepsipeptide antibiotic clinically used to treat serious infections caused by Gram-positive pathogens. Its precise mode of action is somewhat controversial; the biggest issue is daptomycin pore formation, which we directly investigated here. We first performed a screening experiment using propidium iodide (PI) entry to Bacillus subtilis cells and chose the optimum and therapeutically relevant conditions (10 µg/mL daptomycin and 1.25 mM CaCl2) for the subsequent analyses. Using conductance measurements on planar lipid bilayers, we show that daptomycin forms non-uniform oligomeric pores with conductance ranging from 120 pS up to 14 nS. The smallest conductance unit is probably a dimer, however tetramers and pentamers occur in the membrane most frequently. Moreover, daptomycin pore-forming activity is exponentially dependent on the applied membrane voltage. We further analyzed the membrane permeabilizing activity in B. subtilis cells using fluorescence methods (PI, DiSC3(5)). Daptomycin most rapidly permeabilizes cells with high initial membrane potential and dissipates it within a few minutes. Low initial membrane potential hinders daptomycin pore formation.



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