Azalomycin F5a, a polyhydroxy macrolide binding to the polar head of phospholipid and targeting to lipoteichoic acid to kill methicillin-resistant Staphylococcus aureus

Azalomycin F 5a was a polyhydroxy macrolide produced by streptomycete strains. Our preliminary researches indicated that it could kill methicillin-resistant Staphylococcus aureus (MRSA) likely by increasing the permeability of cell membrane, and that cell-membrane phospholipids were likely important targets. To confirm this, membrane permeability assay was performed and visualized by fluorescence staining, and then the detailed interactions between azalomycin F 5a and model membranes prepared with 1,2-dihexadecanoyl- sn -glycero-3-phospho-(1'- rac -glycerol) (DPPG) were determined using attenuated total reflectance fourier transform infrared spectroscopy and 31 P nuclear magnetic resonance techniques. The results indicated that there were strong interactions between azalomycin F 5a and model membranes, especially between azalomycin F 5a and the polar head of phospholipid. For further evidence and details, the molecular dynamics (MD) simulation of the interactions between azalomycin F 5a and DPPG or lysyl-DPPG were performed using Amber16 software package. A strong interaction between the lactone ring of azalomycin F 5a and the polar head of DPPG or lysyl-DPPG had been clearly observed. Moreover, a larger distribution probability out of phospholipid bilayer had been discovered for the guanidyl side chain of azalomycin F 5a , especially when probable anion molecules anchoring on the cytoplasmic membrane occurred. Therefore, lipoteichoic acid (LTA), a vital component of gram-positive bacterial envelope, was investigated for its probable interactions with azalomycin F 5a using broth microdilution method. The results showed that azalomycin F 5a -induced MRSA lysis could be prevented by LTA. This deduced that there were some interactions between azalomycin F 5a , more likely its guanidyl side chain, and LTA. Thereby, azalomycin F 5a increasing the cell-membrane permeability of MRSA had likely achieved by the synergy of its lactone ring binding to the polar head of phospholipid and its guanidyl side chain targeting to LTA, and which had eventually led to the autolysis of MRSA cells.