Comparison of the Effects of Daptomycin on Bacterial and Model Membranes
Ming-Tao Lee, Pei Yin Yang, Nicholas E. Charron, Meng-Hsuan Hsieh, Yu-Yung Chang, Huey W Huang
Daptomycin is a phosphatidylglycerol specific, calcium dependent membrane-active antibiotic that has been approved for the treatment of Gram-positive infections. A recent Bacillus subtilis study found that daptomycin clustered into fluid lipid domains of bacterial membranes and the membrane binding was correlated with dislocation of peripheral membrane proteins and depolarization of membrane potential. In particular, the study disproved the existence of daptomycin ion channels. Our purpose here is to study how daptomycin interacts with lipid bilayers so as to understand the observed phenomena on bacterial membranes. We performed new types of experiments using aspirated giant vesicles with ion leakage indicator, making comparisons between daptomycin and ionomycin, performing vesicle-vesicle transfers and measuring daptomycin binding to fluid phase vs. gel phase bilayers and bilayers including cholesterol. Our findings are entirely consistent with the observations on bacterial membranes. In addition, daptomycin is found to cause ion leakage through the membrane only if its concentration in the membrane is over a certain threshold. The ion leakage caused by daptomycin is transient. It occurs only when daptomycin binds the membrane for the first time; afterwards they cease to induce ion leakage. The ion leakage effect of daptomycin is not transferrable from one membrane to another. The membrane binding of daptomycin is reduced in the gel phase versus the fluid phase. Cholesterol also weakens the membrane binding of daptomycin. The combination of membrane concentration threshold and differential binding is significant. This could be a reason why daptomycin discriminates between eukaryotic and prokaryotic cell membranes.
Fluorescence, Kinetics, Membrane structure, Chemical stability, Biochemistry