The researchers have gained fundamental new insights into the degradation of the amino acid lysine - carcinogenic onco-metabolites as intermediate products.

In fact, they were looking for a specific enzyme. What they found is something so fundamental that their new findings might well find their way into textbooks. Referred to here is the amino acid lysine, which is an important building block in proteins. In bacteria and many other organisms, lysine generates energy during degradation. "We thought that there was nothing more to discover in this field. Then it occurred to us that for many bacteria so far nothing is known about how lysine is degraded," says the senior author. This even applied for the organism which is by far the most thoroughly studied: The bacterium Escherichia coli, in short E. coli - microbiology's model organism per se. The results of the collaborative work conducted by researchers can be found in the journal Nature Communications.

Lysine degradation was so far unknown in many bacteria. The new pathway discovered by the researchers has closed this knowledge gap. "It's a completely new pathway that follows a route so far unknown," says the senior author. To date, lysine was considered to be one of two amino acids where sugar cannot be obtained directly out of their degradation pathway. It was considered to be solely ketogenic instead of glucogenic. This means that precursors for fatty acid metabolism are obtained during degradation. Lipids can be synthesized from this, for example. However, the synthesis of sugars from simple building blocks is very important for metabolism.

Important findings were obtained while describing the various degradation stages: The scientists were able to identify glutarate and hydroxyglutarate as metabolic products, amongst others. The researchers mastered the structural characterization of the key enzyme glutarate hydroxylase by solving the crystal structure. They were also able to show that the oxidation of hydroxyglutarate to the central metabolic product α-ketoglutarate is coupled with the respiratory chain. Above all, however: With succinate as the endpoint of the metabolic pathway, they were able to prove for the first time that lysine can be degraded in a glucogenic manner

The compound hydroxyglutarate, which had not been described previously as a metabolic intermediate, can act as an onco-metabolite in humans. This means that it can accumulate in some forms of cancer and promote tumor growth. That hydroxyglutarate might play a role in cancer already at the development stage is a topic of discussion. "If the detoxification of this compound is disrupted, then this could contribute to the development of cancer," says another author. To date, scientists were not aware of any specific role for this oncometabolite. It was regarded as metabolic waste. "We've found out that at least in many bacteria it's not simply waste but part of a pathway," says the senior author. This makes hydroxyglutarate an intermediate product.

Apart from their role in cancer, glutarate and hydroxyglutarate play important roles in certain hereditary neurodegenerative diseases. If detoxification mechanisms for metabolic products are already defective in the genome, these substances ac-cumulate as a consequence, leading to neurological disorders already in childhood. The scientists can imagine that via organisms such as E. coli, which are able to carry out this degradation pathway in the bowel, these metabolic products enter human cells and must be disposed of there. The researchers is paying more and more attention to the interrelationship between bacteria that colonize the bowel and humans. "Our results justify taking another fresh look at such processes. Perhaps we'll find more links."

https://www.uni-konstanz.de/en/university/news-and-media/current-announcements/press-releases/press-releases-in-detail/Suesser-Lysin-Abbau-16295/
 
https://www.nature.com/articles/s41467-018-07563-6

http://sciencemission.com/site/index.php?page=news&type=view&id=publications%2Fwidespread-bacterial&filter=22