The elucidation of the modes of action of moenomycin and corallorazine A

Abstract

Antimicrobial resistance poses a serious threat to public health worldwide. To overcome this global problem and ensure the supply of effective antibiotics for the therapy of infectious diseases in the future requires to develop innovative anti-infectives with unprecedented and resistance-breaking mechanisms of action and a thorough understanding of their antimicrobial effect on the molecular level. This work investigates the modes of action of two natural product antibiotics, moenomycin and corallorazine A, that target highly conserved structures located on different sites of the bacterial membrane. <br /> The first part of this thesis is devoted to the phosphoglycolipid antibiotic moenomycin, a well-known, potent inhibitor of peptidoglycan glycosyltransferases. Here, it is shown for the first time that the antibiotic possesses an extended target spectrum in <em>Staphylococcus aureus</em> comprising LytR-CpsA-Psr (LCP) enzymes that catalyze the attachment of anionic glycopolymers, such as wall teichoic acids (WTAs) or capsular polysaccharides, to peptidoglycan in Gram-positive bacteria. I showed that LcpA, PBP4, and likely PBP2 are recruited to the septum of moenomycin-treated cells in response to the presumed accumulation of WTA precursors at the division site. Moreover, the combination of moenomycin and β-lactams was synergistic in MSSA1112 wildtype and the TarO-deprived SA113 strain but not in the MSSA1112 <em>ΔlcpABC</em> triple mutant, suggesting that moenomycin reduces the amount of WTAs and/or their attachment to the cell wall. Besides the identification of a so far unknown moenomycin off-target, the results provide new insights into the temporal and spatial coordination of the peptidoglycan and WTA biosynthesis pathways in moenomycin-treated <em>S. aureus</em> cells and could contribute to the development of novel, moenomycin-based antibiotics. <br /> The second part of this thesis focuses on the recently discovered lipodipeptide corallorazine A, a bioactive secondary metabolite synthesized by the myxobacterium Corallococcus coralloides. Using whole cell analysis and <em>in vitro</em> test systems, this work reveals that corallorazine A inhibits the bacterial transcription by targeting the β’-subunit of the DNA-dependent RNA polymerase, a conserved target for antibiotics in prokaryotes. Corallorazine A displayed good antimicrobial activity against Gram-positive bacteria, including methicillin-resistant <em>S. aureus</em>, and could serve as an urgently required broad-spectrum antibiotic. <br /> In summary, this work significantly enhances our understanding of how the antibiotics moenomycin and corallorazine A target relevant bacterial cellular structures.