Neutrons from the research neutron source Heinz Maier-Leibnitz (FRM II) can be used to detect the structure of biomolecules. The most recent success: the precise analysis of a promising vaccine against multi-resistant germs.
Bacteria that are resistant to all common antibiotics cause more than a million deaths every year. Researchers all over the world are therefore looking for new therapeutic approaches against these pathogens.
Two years ago, an international team in Grenoble identified an active ingredient that is suitable for producing a vaccine against multi-resistant bacteria of the Pseudomonas aeruginosa genus. The vaccine has now been successfully tested on mice.
“As with many new vaccines, the active ingredient is embedded in liposomes. Accurately characterizing and understanding these nanoscopic biomolecules is a key factor in the development and optimization of future vaccines,” explains Dr. Marco Maccarini, biophysicist at the Center National de la Recherche Scientifique (CNRS). Together with experts at the TIMC laboratory at the Université Grenoble-Alpes and at the FRM II, he has now succeeded in analyzing the structure of the vaccine candidate against Pseudomonas aeruginosa.
The vaccine consists of biomolecules about 100 nanometers in size. These are mainly formed from fat-like substances, the lipids. Due to their biochemical properties, these lipids form into small vesicles, called liposomes, in which the actual active ingredients are protected and transported. In the case of the vaccine against Pseudomonas aeruoginosa, this active ingredient is the OprF protein.
“In principle, the active ingredient can dock at different positions in the liposome – for example, on the outside or inside,” explains Maccarini. “It is better recognized by the immune system when it is integrated into the double lipid layer. The structure of the biomolecules is therefore crucial for the effectiveness of a vaccine.”
Wanted: Radiation that does not destroy
Such details cannot be seen with the naked eye. Light microscopes also have too low a resolution for examining liposomes. Although X-rays have shorter wavelengths, they are not suitable for structural analysis because under certain circumstances the radiation damages the biomolecules. “Neutron beams, on the other hand, are ideal: They only interact with the atomic nuclei, which does not lead to any damage or structural changes. This allows the samples to be examined in their original state,” explains Maccarini.
At FRM II in Garching near Munich, the researcher found everything he needed to analyze the new vaccine candidate: a high neutron flux, a well-equipped laboratory and Dr. Aurel Radulescu, an expert in measuring small-angle scattering, which allows the detailed study of molecules a few nanometers in size.
Computer model can show structure of vaccines
“The challenge in this case was to use the diffractometer, which measures the scattering of the neutrons by the atomic nuclei, to distinguish between the proteins and the lipids in the sample,” recalls Radulescu, who developed the KWS neutron small-angle facility for Forschungszentrum Jülich in Garching -2 supervised.
This differentiation was finally achieved with a trick: “We carried out the measurements with different solvent combinations – normal water and heavy water containing deuterium, in different mixing ratios.” Because neutrons “see” normal hydrogen and deuterium differently, images of the sample emerged with different contrasts that contain different information.
For the evaluation, the research team developed a computer model that represents the structure of the vaccine candidate. “In this way, we were not only able to visualize the bilayer structure of the lipids, but also to determine the average position and amount of the OprF drug embedded between the two lipid layers.” The new model can also be used to research the structure of new, liposome-based vaccines and to optimize their development.