Recognising structures means understanding structures

HZI researchers perform first structural analysis of amyloid fibres in live organism


Electron micrograph showing an E. coli biofilm, stained in blue. The fibres connecting the individual bacteria are called curli fimbriae.

©HZI / Rohde

Bacteria use adhesive molecules on their cellular surface to colonise a Host. The same type of molecule is also involved in the formation of highly resistant bacterial colonies, called biofilms. Since biofilms are difficult to control, they are often the basis of chronic infections. Scientists from the Helmholtz Centre for Infection Research (HZI) in Braunschweig recently demonstrated a novel approach to the structural analysis of a special class of adhesive molecules called amyloids. The results are published in the renowned professional journal, "Angewandte Chemie".

Amyloids are protein deposits that are found in devastating diseases such as Alzheimer's and Parkinson's. Basically, these are agglomerates of protein molecules which jointly turn into highly stable fibres. The kind of agglomeration and the shape of the fibres are essential for the function of the proteins. Even a minor change in structure can make a basically harmless substance become toxic. "For this reason it is important to exactly know the structure and to know the shape, in which they are present in the body. In an in vitro analysis, one can never be sure if the structure is exactly the same as is present in the body, especially in the case of amyloids," says Prof Christiane Ritter, who is the director of the NMR platform at the HZI and previously was director of the centre's junior research group, "Macromolecular Interactions".

Various bacteria have been successful in producing amyloids in non-toxic form and utilising them for their own purposes. Produced, for example, by the bacterial pathogens, Escherichia coli and Salmonella typhimurium, curli fimbriae are some of the best-known bacterial amyloids. Rader and her team recently where the first to isolate sufficient amounts of curli fimbriae from bacterial biofilms for structural characterisation. Although filament-like structures can be analysed by means of solid body-NMR spectroscopy, the bacteria need to grow on special growth media for this purpose to make the fimbriae "visible" to the NMR spectroscopist. "This allowed us to get a spectroscopic fingerprint of the curli fimbriae. But the patterns were too complex for complete structural analysis," says Ritter.

For this reason, she and her colleagues used a biochemical trick (so-called Protein trans-splicing) to make a single segment of the curli protein visible - without changing the native structure of the protein. This allowed her and her colleagues to be the first to see the shape of curli fimbriae and to compare their results to the spectroscopic fingerprint of the Biofilm material. "We were thus able to show that curli is made up of repetitive segments and that the structure is very similar both in vitro and in vivo,“ says Ritter.

Although the path to new medications or diagnostic procedures is still long, these results mean a major step forward in terms of methodology. "We demonstrated that our methods and analytical procedures are suitable for obtaining information about the shape of entities in the live organism," says Ritter.

Original publication:

Tobias Schubeis, Puwei Yuan, Mumdooh Ahmed, Madhu Nagaraj, Barth-Jan van Rossum, and Christiane Ritter. Untangling a Repetitive Amyloid Sequence: Correlating Biofilm-Derived and Segmentally Labeled Curli Fimbriae by Solid-State NMR Spectroscopy. Angewandte Chemie. 2015 Oct 16. DOI:10.1002/anie.201506772