A novel synergistic antimicrobial mechanism of azalomycin F acting on lipoteichoic acid synthase and cell envelope

Abstract Lipoteichoic acid (LTA) plays an essential role in bacterial growth and resistance to antibiotics, and LTA synthetase (LtaS) was considered as an attractive target for combating Gram-positive infections. Azalomycin F, a natural guanidyl-containing polyhydroxy macrolide, can target the LTA of Staphylococcus aureus. To clarify the detailed mechanism, here the experimental results indicated that azalomycin F can accelerate the LTA release and disrupt the cell envelope, and also led to the feedback upregulation on the expressions of LtaS and other related enzymes. Simultaneously, the reconstituted enzyme activity evaluations showed that azalomycin F can significantly inhibit eLtaS, the extracellular catalytic domain of LtaS. Subsequently, the fluorescence analyses for five incubation systems, together with mass spectroscopy analyses and molecular dockings, indicated that azalomcyin F can spontaneously bind to LtaS active center involving the binding sites of substrates and the LTA prolongation. All these concluded that azalomycin F can inhibit LTA biosynthesis through the interactions of its guanidyl side chain with LtaS active center, and disrupt cell envelope through the synergistic effect of accelerating the LTA release, damaging the cell membrane and electrostatically interacting with LTA. Thereout, it presents a novel synergistic antimicrobial mechanism, and which would eventually the autolysis of S. aureus.