Weak interaction with putative phosphatidyl glycerol head group is critical for the uptake of daptomycin to bacterial membrane

Daptomycin is a potent lipopeptide antibiotic treating life-threatening infections by Gram-positive pathogens. It has been known that susceptibility to this drug increases with increasing content of phosphatidylglycerol, a phospholipid rich in bacterial membranes, whereas a decrease of this phospholipid is closely associated with resistance to the antibiotic. However, the underlying mechanism is not known. Here we measure the kinetic of the uptake of daptomycin into model membrane and show that it is indeed completely dependent on the content of phosphatidylglycerol. Interestingly, the putative headgroup of the phospholipid, sn-glycerol-3-phosphate (G3P), significantly inhibits the drug uptake at millimolar concentrations, strongly suggesting a weak interaction between the drug and the phospholipid headgroup. This weak interaction is further studied and confirmed by fluorescence-based thermal shift and nuclear magnetic resonance (NMR) spectroscopy. Taken together, these results support that the weak interaction between the phosphatidylglycerol headgroup and daptomycin plays a critical role in the uptake of the drug to bacterial membranes.