UNIVERSITY OF TÜBINGEN: Research team from DESY and the Universities of Tübingen and Siegen investigates network formation and protein dynamics

With DESY’s X-ray light source PETRA III, a research team has analyzed the structural changes in eggs during cooking. The study shows how the proteins in chicken egg white unfold and network when heated to form a solid structure. The innovative investigation method is interesting for the food industry as well as for the large field of protein analysis in research, such as the cooperation between the groups of Professor Frank Schreiber from the University of Tübingen and Professor Christian Gutt from the University of Siegen together with researchers from DESY and the European X-ray laser European XFEL with two specialist publications in the journal Physical Review Letters shows.

Eggs are one of the most diverse ingredients in food. They can form gel or foam or be comparatively solid and also serve as the basis for emulsions. At around 80 degrees Celsius, egg white, also called egg white, becomes solid and also optically opaque. This is because the proteins in the egg white form a network structure when heated. In order to examine the exact molecular structure of protein, short-wave radiation such as X-ray light is necessary, which penetrates the opaque protein and whose wavelength is no longer than the structures to be examined.

Controlled heating
“In order to understand the structural change in detail, one has to examine the phenomenon on the micrometer scale,” explains the lead author of the first study, the Alexander von Humboldt scholarship holder Dr. Nafisa Begam from Schreiber’s group. The researchers used what is known as X-ray photon correlation spectroscopy (XPCS) in a specific geometry so that the structure and dynamics of the proteins in the protein could be determined at the same time.

For their experiments at measuring station P10 at PETRA III, the scientists used a commercially available chicken egg and filled the protein into a quartz tube with a diameter of 1.5 millimeters. “The protein was heated in a controlled manner while we analyzed it with X-ray light,” reports co-author Fabian Westermeier from DESY. “The X-ray beam was widened to 0.1 by 0.1 millimeters so that the radiation dose did not damage the protein structures.”

Exponential networking in the three-minute egg
The measurement shows the protein dynamics in the egg white for around a quarter of an hour. In the first almost three minutes, the protein network grew exponentially and after about five minutes reached a plateau on which almost no further protein links formed. The mean mesh size of the protein network after this time was approximately 0.4 micrometers (thousandths of a millimeter).

The P10 beam guidance at DESY’s X-ray light source PETRA III, where the experiments took place.
In the second study, the team used the XPCS technique to examine the self-organization of protein solutions into protein-rich and protein-poor domains as an example of structure formation in cell biology. The temperature-dependent dynamics could be followed over time. “With a high protein concentration, mobility decreases, which slows down the development of phase separation. This is important for the special dynamics of the system, ”reports the lead author Anita Girelli from Schreiber’s group.

The studies funded by the Federal Ministry of Education and Research (BMBF) not only show new details on structural changes in protein, but also substantiate the research concept, which can also be used with other samples, as the second study shows. “The successful application of X-ray photon correlation spectroscopy opens up a new way of studying the dynamics of biomolecules, which is essential to really understand them,” emphasizes Schreiber.

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