The NanoComBac project, funded under grant 16GW0223 and carried out from 1 April 2019 to 31 March 2023, addressed the urgent need for new antibiotics that can penetrate the formidable outer membrane of Gram‑negative bacteria and overcome rising resistance, including that of Mycobacterium tuberculosis. The research team at Ruhr‑Universität Bochum’s Metzler‑Nolte group developed a dual‑mode strategy that couples two distinct antibacterial agents—actinonin and moiramid—with a gold‑nanoparticle carrier. Actinonin is a peptide natural product that inhibits the bacterial metalloprotease peptide‑deformylase (PDF), thereby blocking the removal of the formyl group from nascent proteins. Moiramid, a peptide inhibitor of the biotin‑dependent acetyl‑CoA carboxylase (ACC) enzyme, targets fatty‑acid synthesis and has shown activity against both Gram‑positive and certain Gram‑negative strains. Neither compound has been exploited by commercial antibiotics, and both suffer from limited membrane penetration and, in the case of actinonin, off‑target toxicity to human mitochondrial PDF.

The core technical achievement of the project was the reproducible synthesis of small gold nanoparticles (2–5 nm diameter) functionalised with thiol‑modified derivatives of actinonin. The gold surface provides an inherent antibacterial effect and serves as a Trojan horse to ferry the natural product across the outer membrane. Binding of the actinonin‑loaded nanoparticles to bacterial PDF was confirmed by multidimensional nuclear magnetic resonance spectroscopy in solution, and the crystal structure of the PDF–inhibitor complex was solved by X‑ray diffraction, providing detailed insight into the interaction interface. Antibacterial assays demonstrated that the conjugates retain, and in some cases enhance, the activity of actinonin against a panel of Gram‑negative pathogens, including drug‑resistant strains. Importantly, the same conjugates exhibited measurable activity against M. tuberculosis, a finding that was validated in a collaboration with the University of Cologne’s Dr. Rybniker group. In parallel, the team synthesized a thiol‑modified biotin derivative that was immobilised on gold nanoparticles, enabling pull‑down experiments to identify additional protein targets of the conjugates; these studies are currently being prepared for publication.

The project’s collaborative framework was essential to its success. The Metzler‑Nolte group handled nanoparticle synthesis and functionalisation, while the Stoll group provided expertise in protein biochemistry and structural analysis. The Bandow group performed microbiological testing, and the LDC (Leibniz‑Centre for Molecular and Applied Biosciences) contributed further biological assays. AG Scherkenbeck assisted with nanoparticle production, and the consortium’s partners at the University of Wuppertal and the University of Cologne expanded the scope to include tuberculosis research. The consortium’s integrated approach, combining chemistry, structural biology, and microbiology, has laid a solid foundation for the development of next‑generation, resistance‑breaking antibiotics that exploit novel mechanisms of action and innovative delivery platforms.