Research Team Investigates RNR Protein in Living Cells

For the functioning of cells in the human body, proteins perform important tasks. Depending on the type of protein they can, for example, transport metabolic products, enable cell movements, protect against infections, or catalyze biochemical reactions. In carrying out all of these tasks, the proteins are in constant exchange with their environment and interact with other proteins as well as with other cell components. To gain a better understanding of the functional mechanisms of cells, therefore, it is of great importance to better understand the structure and properties of particular proteins.

This is where the research of JProf. Kasanmascheff comes in: For her current publication, she and her research team analyzed the protein ribonucleotide reductase (RNR), which is indispensable for the production of DNA building blocks in the cells of nearly all plants and mammals, including humans. What’s special about this project is that all of the experiments were carried out in vivo, that is, in living cells instead of the usual artificial, in vitro environment. “We wanted to find out to what extent the actual structure and function of the RNR in living cells differs from the results of in vitro research,” Kasanmascheff says.

Electron spin resonance spectroscopy makes processes in cells visible

For her investigations, the junior professor uses the method of electron spin resonance spectroscopy (ESR spectroscopy). This works in a way that is similar to magnetic resonance imaging (MRI), which is commonly used in medical diagnostics. In both methods, a magnetic field causes certain particles to be excited and emit signals that can be recorded: In MRI, the spins of atomic nuclei are excited; in contrast, it is the spins of unpaired electrons within molecules that are excited in electron spin resonance spectroscopy. “This method is especially well suited for visualizing the structure and processes inside cells and involving proteins, because such unpaired electrons are the starting point for numerous chemical reactions in the cells and also occur in RNR,” explains JProf. Kasanmascheff. Molecules with unpaired electrons are generally referred to as radicals.

In the structure of RNR, there are two special radicals. They possess a so-called di-iron cofactor that enables the protein’s catalytic activity. Using ESR spectroscopy, the scientists were able to show that the structure and properties of the di-iron cofactor in the RNR of living E. coli bacteria do in fact correspond to those previously observed in vitro. On the basis of the experiments, however, the team also discovered that the regulation of RNR catalysis in living cells is different from what was observed in vitro. In vivo, both radicals of the RNA are not always involved in the catalysis; sometimes it is only a single one. These findings support the thesis that the activity of the RNR protein in living cells is regulated by changes in the concentration of the di-iron cofactor.

The results could also have relevance for cancer research

In another experiment, the Dortmund research team was also the first to succeed in inserting an artificial amino acid in place of the radical in the RNR protein of a living cell and then observing it. Using this artificial amino acid, it is also possible to influence the enzyme’s activity. This could prove to be an important step toward selectively influencing and manipulating the behavior of living cells in the future, Kasanmascheff says. The results are particularly relevant for cancer research, since cells always require RNR when they divide or need to repair damage to the DNA. If it were also possible to influence RNR activity in tumor cells in a targeted manner, the growth of tumors could be slowed down or even stopped completely.

Kasanmascheff and her team have published the results of this research, which was carried out within the framework of the Cluster of Excellence RESOLV, funded by the German Research Foundation (DFG), in the scientific journal An­ge­wand­te Chemie. The publication was honored as a “highly important paper,” a distinction awarded to only around ten percent of the papers published in the journal.

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