Modes of action of tunicamycin, liposidomycin B, and mureidomycin A: Inhibition of phospho-N-acetylmuramyl-pentapeptide translocase from Escherichia coli

Abstract

Using a continuous fluorescence-based enzyme assay, we have characterized the antibacterial agents tunicamycin and liposidomycin B as inhibitors of solubilized Escherichia coli phospho-N-acetylmuramyl- pentapeptide translocase. Tunicamycin exhibited reversible inhibition (K(i) = 0.55 ± 0.1 μM) which was noncompetitive with respect to the lipid acceptor substrate and competitive with respect to the fluorescent substrate analog, dansyl-UDPMurNAc-pentapeptide. Liposidomycin B exhibited slow-binding inhibition (K(i) = 80 ± 15 nM) which was competitive with respect to the lipid acceptor substrate and noncompetitive with respect to dansyl-UDPMurNAc- pentapeptide. These results provide insight into the molecular mechanisms of action of these two classes of nucleoside antibiotics.