Lipodepsipeptide empedopeptin inhibits cell wall biosynthesis through Ca2+-dependent complex formation with peptidoglycan precursors

Empedopeptin is a natural lipodepsipeptide antibiotic with potent antibacterial activity against multiresistant Gram-positive bacteria including methicillin-resistant Staphylococcus aureus and penicillin-resistant Streptococcus pneumoniae in vitro and in animal models of bacterial infection. Here, we describe its so far elusive mechanism of antibacterial action. Empedopeptin selectively interferes with late stages of cell wall biosynthesis in intact bacterial cells as demonstrated by inhibition of N-acetylglucosamine incorporation into polymeric cell wall and the accumulation of the ultimate soluble peptidoglycan precursor UDP-N-acetylmuramic acid-pentapeptide in the cytoplasm. Using membrane preparations and the complete cascade of purified, recombinant late stage peptidoglycan biosynthetic enzymes and their respective purified substrates, we show that empedopeptin forms complexes with undecaprenyl pyrophosphate containing peptidoglycan precursors. The primary physiological target of empedopeptin is undecaprenyl pyrophosphate-N-acetylmuramic acid(pentapeptide)-N-acetylglucosamine (lipid II), which is readily accessible at the outside of the cell and which forms a complex with the antibiotic in a 1:2 molar stoichiometry. Lipid II is bound in a region that involves at least the pyrophosphate group, the first sugar, and the proximal parts of stem peptide and undecaprenyl chain. Undecaprenyl pyrophosphate and also teichoic acid precursors are bound with lower affinity and constitute additional targets. Calcium ions are crucial for the antibacterial activity of empedopeptin as they promote stronger interaction with its targets and with negatively charged phospholipids in the membrane. Based on the high structural similarity of empedopeptin to the tripropeptins and plusbacins, we propose this mechanism of action for the whole compound class.