Ubiquitin’s ability to label synthetic compounds offers a new path to discover drugs

Small but powerful: Ubiquitin controls the lifespan and distribution of proteins in the cell, but it can also determine their form, function or interactions with other cellular components. Ubiquitin ligases are essential to this process because they reliably recognize relevant proteins among tens of thousands of molecules and allow correct instructions. Disturbances in this precise marking routine can cause cellular processes and defective diseases such as cancer.

Conversely, drugs can be designed to modulate Ubiquitin ligases, by ordering them to mark specific proteins promoting disease with Ubiquitin for degradation. However, this principle currently only applies some of the more than 600 human ubiquitin ligases.

Ubiquitin Ligase Huwe1 is an interesting but unexploited target for therapeutic strategies with important roles in tumors and neurodevelopmental disorders. Although drug -like compounds have been used to inhibit Huwe1 in scientific research, their mechanism of action has remained clear, which hinders their advancement in potential therapeutic agents.

Difficult discovery process

A team led by Sonja Lorenz at the MPI for the multidisciplinary sciences has now disentangled the unexpected mechanism by which these compounds act. Using an interdisciplinary approach, researchers combined protein biochemistry, cell biology and click chemistry.

Other key methods for the success of the project have been the tailor -made molecular syntheses of medicinal chemists led by Matthias Gehringer at the University of Tübingen, as well as mass spectrometric measures by the research group of Henning Urlaub and the simulations of molecular dynamics by colleagues of Helmut Grubmüller in the Department of MPI, Lorenz

Competition instead of inhibition

“We have found that the medication type compounds marketed as Huwe1 inhibitors interact with this enzyme, but they do not inhibit it. Rather, Huwe1 recognizes the compounds themselves as target molecules and brand with ubiquitin,” reports Lorenz.

“When the drug -type compounds are provided in excess on a natural target protein in the test tube, they consume ubiquitin. This competition between medication type compounds and target protein is what had been misinterpreted as Huwe1 inhibition,” adds Pavel Pohl, one of the main authors of the study now published in the newspaper, Nature communications.

The team also managed to demonstrate, for the first time, that the synthetic compounds are tagged with ubiquitin in living cells. However, the situation here is much more complex than in the test tube.

“In the cell, Huwe1 promotes the ubiquitination of compounds, but he does not pilot it exclusively,” explains Barbara Orth, another main author of the study. This implies that cellular ubiquitination enzymes other than Huwe1 can also label medicine -type molecules with ubiquitin. This observation is of fundamental importance because Ubiquitin’s signals had previously been observed only on proteins, sugars and other biomolecules in cells, but not on synthetic compounds.

“The new substrate spectrum will be particularly interesting for therapeutic and biotechnological applications in the field of ubiquitin. Our discovery offers tangible strategies to develop new molecular tools to modulate the cellular system of Ubiquitin and, in turn, influences the disease processes”, explains Lorenz.