Droplet Formation by Enzymes Accelerates Cellular Signaling

Researchers at the Massachusetts Institute of Technology have uncovered key insights into how enzymes, specifically kinases, form droplets within cells to accelerate and alter vital signaling reactions. The study, published in Cell Reports, reveals that this process, known as phase separation, may be critically important for cellular organization and function, with implications for drug development against diseases such as cancer.

Over the past decade, biologists have discovered that phase separation—where certain proteins condense into dense droplets within the cell—serves as an important organizational strategy. Similar to how oil droplets separate from vinegar, proteins inside cells can cluster together, enabling higher concentrations and specialized biochemical environments.

The MIT team, led by assistant professor Lindsay Case, focused on a class of enzymes called kinases. These proteins activate other proteins by adding phosphate groups, a process integral to cell signaling. The researchers showed that when kinases form droplets, their catalytic activity increases, enabling them to activate signaling pathways more rapidly. In some instances, droplet formation can even result in the kinases targeting different proteins than they would in their typical, dispersed state.

Key experiments involved the enzyme focal adhesion kinase (FAK), which is activated when cells attach to surrounding structures. By artificially overexpressing FAK in cells, the researchers induced phase separation, prompting FAK to form droplets even in unattached conditions. This led to the unexpected activation of pro-growth signaling, suggesting that abnormally high concentrations can trigger excessive signaling, as seen in cancer cells.

The findings raise the possibility that interfering with droplet formation might be a novel strategy for designing cancer treatments, by preventing kinases from sending persistently active signals that promote disease progression.

The researchers also extended their investigation to two additional kinases, Mst2 and Abl, finding both could phase separate and that this enhanced their enzymatic activity. In the case of Mst2, the mechanism appears to be used by healthy cells to precisely regulate important growth and survival pathways. Interestingly, in these droplet states, the kinases were observed to phosphorylate a broader array of targets, demonstrating that organization at the molecular level can change the nature and complexity of cellular signaling.

Machine learning was used to predict that nearly half of the 500 known human kinases likely have the capacity to form droplets. Those identified tend to have a highly positive charge, correlating with the tendency to attract ATP—the molecule kinases rely on as a phosphate donor—into the droplets. This recruitment of ATP may further enhance the efficiency of signaling reactions.

Looking forward, the research suggests that drugs could be designed to better target specific enzyme droplets inside cells, thereby increasing precision and reducing potential side effects. By concentrating therapeutic agents within the same compartment as their target enzymes, it could be possible to achieve more effective and selective treatments for diseases marked by kinase overactivity.

The study was funded by multiple sources, including the Searle Scholars Program, the U.S. Air Force Office of Scientific Research, and the National Institutes of Health.

Reference: news.mit.edu{:target="_blank"}