Clumps of the protein FUS, which are a pathological characteristic of ALS and frontotemporal dementia, can be prevented through a biological process called phosphorylation, a new study shows.
The study, “Phosphorylation of the FUS low‐complexity domain disrupts phase separation, aggregation, and toxicity,” was published in the EMBO Journal.
Phosphorylation is a common reaction that takes place in every cell throughout the body. Proteins especially undergo phosphorylation as part of post-translational modification, which is the further modification of protein that occurs after it has been produced but before it is fully functional. Phosphorylation refers to the addition of a phosphate molecule to a protein, which introduces a negative charge and causes the negatively charged proteins to repel each other.
One of the domains present in the FUS protein is known to be targeted for phosphorylation, indicating that there are specific sites on the protein that can undergo phosphorylation. However, FUS is almost completely uncharged.
Researchers at Brown University and the Uniformed Services University set out to explore the phosphorylation sites on this protein as a potential way to avoid aggregation, or clumping. They first mapped all of the phosphorylation sites on the protein, and with more than a dozen identified, they investigated the effect of phosphorylation on those sites.
Researchers inserted phosphorylated human FUS into yeast models and induced phosphorylation of FUS in human cells. In both experimental systems, they showed that by increasing phosphorylation, the tendency of the proteins to clump together decreased. This effect was proportional to the number of sites that were phosphorylated.
Researchers were able to fully separate FUS clumps in yeast cells that were heavily phosphorylated. This led to an increase in the robustness of yeast colonies, indicating that FUS clumping is harmful to cells.
“No one has shown that you can use charge, and phosphorylation as a way to get charge, to disrupt these ALS-associated protein aggregates,” study co-author Nicolas Fawzi, assistant professor at Brown University’s Department of Molecular Pharmacology, Physiology and Biotechnology, said in a press release.
Researchers also looked at the way that FUS structure changes as it undergoes phosphorylation. Using a method called nuclear magnetic resonance spectroscopy, scientists were able to demonstrate that the structure of FUS was well-preserved after phosphorylation. They were able to show that the degree of self‐interaction between individual FUS molecules was reduced by phosphorylation. Computer modeling of the phosphorylation-induced effects showed that this reduction in protein clumping is likely due to the introduction of a negative charge.
While using this approach to prevent FUS clumps in a clinical setting remains in the distant future, the authors note that if there was a way to engineer artificial phosphorylation in ALS patients as a targeted therapy for motor neurons, it could become an effective treatment strategy. Currently, many pharmaceutical companies are investigating the use of kinases, which are enzymes that conduct phosphorylation, in various disease settings.
“There’s no therapy or cure for ALS and frontotemporal dementia,” Fawzi said. “What we need are new hypotheses and new angles.”
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