How cells process and dispose of damaged proteins

In a new paper with what Eric Streiter, a senior author at the University of Massachusetts Amherst, called “extremely surprising” results, he and his chemistry lab group report that they have discovered how an enzyme called UCH37 manages cell waste management systems. .

“It took us eight years to figure it out, and I’m very proud of that work. We had to develop many new methods and tools to understand what this enzyme does,” says Streiter.

As he explains, a very large protease called a protease is responsible for degrading most proteins in the cell; It can be made up of up to 40 proteins. It has been known for more than 20 years that UCH37A is one of the regulatory enzymes associated with proteasomes, he adds, “but no one understood what it was doing.”

It turns out that the jaws of the whole process, he adds, can be a complex change in a small protein called ubiquitin. “In addition to modifying other proteins, ubiquitin modifies itself resulting in a wider range of chains. Some of these chains may have extended branches. We have found that UCH removes branches from 37 chains, and allows degeneration to continue.”

Write in this week Molecular cell, He and the first author and Ph.D. Candidate Kirandeep Deol, who led the experiments and experimented with co-authors Sean Crow, Gial Du, Heather Bisby and Robert Gunnett, discussed how they answered the question. This work was supported by the National Institute of General Medical Sciences, NIH.

This could lead to new cancer treatments in advance, Streiter says, because cancer cells need proteasomes to grow and spread. “Many cancer cells are essentially addicted to proteosome function,” he says. “Its cells produce proteins at such a rapid rate that errors occur, and cells cannot function if these are not cleaned. UCH37 helps clear proteins, so it may be a useful therapeutic target to add proteosome inhibitors.” Which has already been successful in the clinic. “

To begin their years-long process, Streiter says, “We had to move forward with a way to generate different types of ubiquitin chains that represent potential variations in the cell. That new library of ubiquitin chains allowed us to make inquiries using it in a controlled setting. The activity of UCH37. That series of experiments gave us the first clue that this enzyme was doing something unique. “

Another new method they developed, using mass spectrometry to characterize the architecture of ubiquitin chains in complex mixtures. “This showed that the activity we discovered with the library of the substrate was also in a more heterogeneous mixture,” says Streiter. Finally, chemists used the CRISPR gene acquisition tool to remove UCH37 from cells to measure the effect of UCH37 on proteosome-mediated degradation in vitro and in cells.

One more surprise with this technology. “Instead of acting as expected and resisting the degradation process, it turns out that UCH37 is removing branchpoints from the ubiquitin chains to help the protein degrade,” says Stratter. “You would think that removing the sign of degeneration would lead to degeneration,” but it didn’t work that way. “

In future experiments, Streiter and colleagues hope to further explore the process of degeneration and learn in more detail how to control UHC37 cellular function.