Heinrich-Heine-Universität - Fach Pharmazie




Research focus

  • Molecular mechanisms of antibiotic action
  • Novel antibacterial targets
  • Novel lead structures for antibacterial drug discovery 
  • Antibiotic resistance

Antibacterial Drug Discovery & Development of Antimicrobial Resistance

Bild4.pngSince the 1940s we have experienced the impressive potential of antibiotics in reducing morbidity and mortality. However, over the last two decades this achievement is increasingly threatened by bacterial resistance development. Worse, the number of antibiotic drug approvals is constantly declining. Nowadays, multidrug resistant pathogens challenge the treatment of serious nosocomial and community-acquired infections. There is an urgent need to evaluate novel antimicrobial agents with new modes of action that are devoid of pre-existing cross-resistances to provide alternatives to commonly applied antibiotics (...more). Considering the strong ability of bacteria to respond to any antibiotic treatment by genetic as well as physiological adaptations, it is important to study and develop successful antibacterial mechanisms with reduced potential for resistance development (...more). 

Molecular Mode of Action of Antibiotic Acyldepsipeptides

adep1.jpgWe investigate a novel class of acyldepsipeptides (designated ADEPs) with prominent antibacterial activity against Gram-positive pathogens including streptococci, enterococci as well as multidrug-resistant Staphylococcus aureus (MRSA) (...more). ADEPs act via an unprecedented mechanism by dysregulating ClpP, the proteolytic core of the bacterial ATP-dependent caseinolytic protease. ClpP, a crucial factor in maintaining vital cellular functions, is a tightly regulated protein which is unable to degrade proteins on its own and strictly depends on Clp-ATPases and accessory proteins for proteolytic activation. Clp-ATPases are indispensable for recognizing, unfolding, and feeding the protein substrates through the tiny entrance pores into the proteolytic chamber of ClpP. We showed that ADEPs overcome these strict control mechanisms by turning ClpP into an uncontrolled protease that now degrades flexible proteins like casein in the absence of Clp-ATPases (...more).
adep-clpP complex.jpg

ADEPs trigger oligomerization of ClpP monomers and activate the resulting tetradecamer to bind and degrade unfolded, nascent polypeptides and flexible proteins independently. Additionally, ADEPs abrogate the interaction of ClpP with cooperating Clp-ATPases, thus preventing degradation of its physiological substrates and all natural functions of ClpP (...more). Using crystal structure determinations and electron microscopic images of ClpP in complex with ADEPs, our studies provided a rationale for these pore opening2.jpgbiochemical observations. The ADEPs increase subunit interaction between ClpP monomers, compete with the Clp-ATPases for the same binding site, and trigger a closed- to open-gate structural transition of the substrate entrance pore, which is otherwise tightly closed (...more).

celldivinhih.jpgRecently, we identified the specific series of events from the physiological point of view that finally leads to death of ADEP-treated bacteria. Fluorescence microscopy techniques and accompanying biochemical studies showed that ADEP prevents cell division in Gram-positive bacteria and induces strong filamentation of rod-shaped Bacillus subtilis and swelling of coccoid S. aureus and Streptococcus pneumoniae. It emerged that ADEP treatment inhibits septum formation at the stage of Z-ring assembly, and that central cell division proteins delocalize from mid-cell positions. This effect was due to the proteolytic degradation of the essential cell division protein FtsZ which appeared to be particularly prone to degradation by the ADEP-ClpP complex (...more). 

By deregulating bacterial ClpP peptidase to degrade the essential cell division pacemaker protein FtsZ and thus prevent cell division, ADEP inhibits a vital cellular process of bacteria that is not targeted by any therapeutically applied antibiotic so far. Therefore, their unique multi-faceted mechanism of action and antibacterial potency makes them promising lead structures for antibiotic drug discovery.

Molecular Mode of Action of Empedopeptin

empedopeptin2.pngEmpedopeptin is an amphoteric, cyclic lipodepsipeptide antibiotic produced by the Gram-negative soil bacterium Empedobacter haloabium ATCC 31962 with potent antibacterial activity against a broad range of aerobic and anaerobic Gram-positive bacteria, including the important pathogens Staphylococcus aureus, Streptococcus pneumoniae and Clostridium difficile in vitro and animal models of bacterial infection. Despite these interesting features its specific mode of action had remained elusive. We recently found that empedopeptin interferes with the lipid cycle in peptidoglycan synthesis by sequestering lipid II as its primary target and additional lipid intermediates as secondary targets. Lipid II is a highly validated antibiotic target that is also addressed by the marketed antibiotic vancomycin. However, the binding site that empedopeptin recognizes at lipid II differs from that of vancomycin, with the advantage that empedopeptin remains active against vancomycin-resistant isolates. Empedopeptin forms a complex with lipid II in a 2:1 molar stoichiometry of antibiotic to lipid precursor and binds lipid II in a region that involves at least the pyrophosphate group,empedopeptin model.jpg the first sugar and the proximal parts of stem peptide and undecaprenyl chain. Calcium ions increase the antibacterial activity of empedopeptin by strengthening the interaction of the net-negative antibiotic with its target and with phospholipids in the cytoplasmic membran. As empedopeptin has considerable structural similarity to the lipodepsipeptides of the tripropeptin and plusbacin group, we propose this molecular mechanism of action for the whole compound class (more ...).

Current grants



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Group leader:

Prof. Dr. Heike Brötz-Oesterhelt
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Claudia Eckelskemper
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