Tripropeptin C Blocks the Lipid Cycle of Cell Wall Biosynthesis by Complex Formation with Undecaprenyl Pyrophosphate

Tripropeptin C (TPPC) is a naturally occurring cyclic lipodepsipeptide antibiotic produced by a Lysobacter sp. TPPC exhibits potent antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), and penicillin-resistant Streptococcus pneumoniae. This antibiotic also inhibits the incorporation of N-acetylglucosamine into the peptidoglycan of S. aureus at a 50% inhibitory concentration (IC(50)) of 0.7 mu M, which is proportional to its MIC (0.87 mu M; equivalent to 1.0 mu g/ml). Treatment of exponential-phase S. aureus cells with TPPC resulted in accumulation of UDP-MurNAc-pentapeptide in the cytoplasm. The antimicrobial activity of TPPC was weakened by the addition of prenyl pyrophosphates but not by prenyl phosphates, UDP-linked sugars, or the pentapeptide of peptidoglycan. The direct interaction between TPPC and undecaprenyl pyrophosphate (C(55)-PP) was observed by mass spectrometry and thin-layer chromatography analysis, indicating that TPPC can potentially inhibit C(55)-PP phosphatase activity, which plays a crucial role in the lipid cycle of peptidoglycan synthesis. As expected, TPPC inhibits this enzymatic reaction at an IC(50) of 0.03 to 0.1 mu M in vitro, as does bacitracin. From the analysis of accumulation of lipid carrier-related compounds, TPPC was found to cause the accumulation of C(55)-PP in situ, leading to the accumulation of a glycine-containing lipid intermediate. This suggested that the TPPC/C(55)-PP complex also inhibits the transglycosylation step or flippase activity, adding to the inhibition of C(55)-PP dephosphorylation. This mode of action is different from that of currently available drugs such as vancomycin, daptomycin, and bacitracin.