When bacteria and Viruses infest a body, they are recognised as foreign matter by the immune system. This leads to a corresponding immune response in an attempt to control these pathogens. In order to understand the mechanisms of attack of the pathogens in detail and to develop matching agents, researchers need to elucidate the structure of proteins on a molecular level. Only then can they see which structures are under attack and what this looks like in detail. Scientists of the Helmholtz Centre for Infection Research (HZI) in Braunschweig recently developed a new method for elucidation of the structure of very large protein complexes at high resolution. They combined an existing procedure, called solid body NMR spectroscopy, with a specially developed mathematical algorithm. The results are published in the professional scientific journal, "Proceedings of the National Academy of Sciences" (PNAS).
During an infection by a virus our body recognises certain viral molecules as "foreign" and initiates a signalling cascade in an attempt to combat the invaders. A central role in this cascade is played by the "mitochondrial antiviral signaling protein" (MAVS), which the researchers from Braunschweig inspected in much detail. "We decided to study the MAVS proteins because they play an important role for signal transduction of our innate immune system. These proteins react to many different Viruses, mainly RNA-Viruses such as Hepatitis, influenza or Dengue," says Prof Christiane Ritter, who is the director of the Nuclear magnetic resonance spectroscopy platform, or NMR for short, at the HZI. The Protein is present on the mitochondrial membrane, which supplies our cells with energy, and is therefore significantly involved in the defense against infections.
During an Infection by a virus, the Protein agglomerates into a spirally arranged superstructure that was difficult to visualise three-dimensionally at high resolution until now. Combining NMR data with the mathematical algorithm, the researchers could successfully elucidate the symmetry of single molecules on screw-shaped filaments in the MAVS Protein at high resolution.
The principle of NMR spectroscopy is to measure distances between individual atomic nuclei from which an image can be calculated. To be able to correctly determine the structure of protein complexes, the contact sites between the individual components need to be assigned as well. The individual protein molecules need to be studied separately for this purpose. "We solved this problem using biochemical approaches and special sample preparation," Ritter says. The newly developed Algorithm systematically checks all possibilities of symmetry. It goes on to compare the results of these checks to the NMR spectroscopic data to yield an accurate image of the protein.
But this imaging procedure does not only work with MAVS proteins. It might be used in the future by researchers to study any protein complex that comprises symmetrical and filament-like structures. Aside from other signaling proteins, this procedure can also be applied to the investigation of many molecules on the surface of bacteria. The new structural analysis lays the foundation for active-substance research and also contributes to a better understanding of the immune system and its response. This is essential, for example, to be able to develop agents that can intervene in the regulation of our immune system. "The combination of NMR data and a mathematical algorithm for structure determination of helical superstructures is a major advance both in technology and in biology," Ritter says.
Original publication:
Lichun He, Benjamin Bardiaux, Mumdooh Ahmed, Johannes Spehra, Renate König, Heinrich Lünsdorf, Ulfert Rand, Thorsten Lührs and Christiane Ritter. Structure determination of helical filaments by solid-state NMR spectroscopy. PNAS. 2016 Jan 6. DOI: 10.1073/pnas.1513119113.
