Double strike against tuberculosis

Beta-lactone inhibits mycomenbrane biosynthesis and potentiates antibiotics

Dr. Johannes Lehmann (left) and Prof. Stephan A. Sieber examine test results on the antibacterial effect of various substances.
(Foto: Christian Fetzer / TUM)

[27.12.2017] In search of new strategies against life-threatening tuberculosis infections, a team from the Technical University of Munich (TUM), as well as Harvard University and Texas A&M University in the USA have found a new ally. They discovered a substance that interferes with the mycomembrane formation of the bacterium. It is effective even in low concentrations and when combined with known antibiotics their effectiveness is improved by up to 100-fold.

The clumps caused by misfolded proteins, called plaques, are implicated in many diseases: plaque interferes with neuron function in the brains of people with dementia and Alzheimer's. The process of the formation of plaques also kills islet cells, which produce insulin to metabolize sugar, in people with type 2 diabetes.

“In general, toxicity to cells is extremely difficult to prove and characterize,” said Ayyalusamy Ramamoorthy, Professor at the University of Michigan and Hans Fischer Fellow of the Institute for Advanced Study at the Technical University of Munich. “On the other hand, we need to do this in order to develop drugs for potential treatment.”

Lipid Nanodisks stabilize addregating proteins

To understand the critical protein structures, the researchers used “sushi-like” nanodics composed of layers of lipids surrounded by a belt to capture model proteins during the aggregation process.

The researchers allowed the proteins to fold to a certain point within the nanodisc – when they think the folding proteins are most toxic to islet cells – and then used nuclear magnetic resonance (NMR) spectroscopy to take atomic-level images of the proteins.

“The nanodiscs are like the difference between a swimming pool and the ocean. In the ocean, there are no boundaries; a swimming pool has boundaries,” Ramamoorthy said. “We're able to stop the aggregation of the protein in this restricted membrane environment so we can monitor what it looks like before it becomes a mass of fibers."

A first step into development of drugs

The ability to pin down proteins while they’re in the process of amyloid aggregation in a stable manner allow their characterization using a variety of biophysical tools including fluorescence, mass-spectrometry, NMR, and cryo-electron-microscopy. Therewith the researchers hope to both develop and screen for drug compounds that can target the misfolding proteins that are implicated in these diseases.

“We are now screening interactions with small molecule compounds to see if we can inhibit the aggregation process that produces amyloids,” Ramamoorthy said. “This has been much wanted and much awaited information – for the scientific understanding of the pathology of amyloid diseases, and for the development of compounds to overcome these problems.”

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The study was carried out by researchers at the Technical University of Munich, the University of Michigan, and the Helmholtz-Zentrum Muenchen in the framework of the TUM Institute of Advanced Study Focus Group “Protein Misfolding and Amyloid Diseases” where Prof. Ayyalusamy Ramamoorthy worked as TUM-IAS Hans Fischer Senior Fellow hosted by Bernd Reif, Professor for Solid State NMR-Spectroscopy at TUM.

This work was supported by funds from NIH, the Helmholtz-Gemeinschaft and the German Research Foundation, the Cluster of Excellence „Center for Integrated Protein Science Munich (CIPSM) and the Institute for Advanced Study, funded by the German Excellence Initiative and the European Union Seventh Framework Program under grant agreement no. 291763. The Gauss Center for Supercomputing provided computing time at the Leibniz Supercomputing Center in Garching.

Publication:

Johannes Lehmann, Tan-Yun Cheng, Anup Aggarwal, Annie S. Park, Evelyn Zeiler, Ravikiran M. Raju, Tatos Akopian, Olga Kandror, James C. Sacchettini, D. Branch Moody, Eric J. Rubin und Stephan A. Sieber: An Antibacterial ß-Lactone Kills Mycobacterium tuberculosis by Disrupting Mycolic Acid Biosynthesis, Angewandte Chem Int Edition, 2017. doi: 10.1002/anie.201709365

Contact:

Prof. Dr. Stephan A. Sieber
Technical University of Munich
Chair of Organic Chemistry II
Lichtenbergstr. 4, 85748 Garching, Germany
Tel.: +49 89 289 13302

Mail: stephan.sieber@tum.de