In the Fold: New Drug Target Discovered

Five tiny phosphates make a big difference in the way proteins associated with many diseases behave, unlocking a new drug target for certain conditions.

Our bodies are made of millions of cells and each one contains proteins that determine the how the cell works. Until recently, it was thought that proteins needed to fold into a stable structure to function, but many proteins perform their biological role in a disordered state.  Disordered proteins are more difficult to study, but they are important for controlling critical cellular processes and, when this control is lost, it is associated with many health problems.

A team of researchers led by Julie Forman-Kay, a Professor in the Faculty of Medicine’s Department of Biochemistry and  Senior Scientist at The Hospital for Sick Children (SickKids), discovered a mechanism the cell uses for controlling a disordered protein involved in cancer and autism.

The study, published in the journal Nature, shows that a process called phosphorylation — adding phosphates to the protein— can fold the disordered protein to make it non-functional, in contrast to previous expectations.

The research focused on a protein called 4E-BP2, which is associated with autism and cancer.  When 4E-BP2 is disordered, it binds to another protein called eIF4E to prevent a key process called translation, which creates new proteins. But by adding two phosphates, Forman-Kay and her collaborators were able to make the 4E-BP2 fold. And the addition of three more phosphates stabilized the newly folded protein, freeing eIF4E for protein translation.

“Translation is a tightly regulated process switched on and off by a variety of signals,” said Forman-Kay. “Trying to understand that process, and how biology exploits it for cell regulation, is important because it is a fundamental part of biology.”

Forman-Kay likens the proteins and phosphates to magnets with positive and negative ends. If a protein is positive, like the folded domain of 4E-BP2, they attract and stick to the ‘negative’ phosphates. This stabilizes the 4E-BP2 fold.

“This phosphorylation doesn’t just lead to folding,” said Forman-Kay. “The folded structure is incompatible with eIF4E binding. It is a complex mechanism.”

In the brain, proteins play a key role in neural function. The production of too many or too few proteins can cause neurological disorders, including autism. In cancer cells, signals go awry, causing too many proteins to be made.

“People have known about the 4E-BP class of proteins, but from a pharmaceutical perspective, the fact there is now a way to make them fold gives us a new drug target because you’ve got a structure and you can stabilize it or destabilize it,” said Forman-Kay.

“If we can find a small molecule or a drug that can prevent folding, then no matter how many phosphates you have there, it will still bind and prevent translation and the creation of other proteins. Or vice versa,” said Alaji Bah, a post doctoral trainee in Forman-Kay’s lab and the paper’s first author. “In cancer, as the cancer cells are dividing, they need more proteins to make new cells, so if you can stop those cells from making more protein, you can starve the cancer.”

One of Forman-Kay lab’s collaborators, Nahum Sonenberg, a researcher based at McGill University in Montreal, is working with pharmaceutical companies to target protein translation in cancer cells.

In addition to revealing a new mechanism to control cellular function, the findings also settle a scientific debate that is two decades old.

“For 20 years, there’s been debate about why phosphorylation prevents binding with the protein eIF4E, ” said Forman-Kay. “We showed that the simple ideas of negative charge repulsion as a mechanism are wrong,” she said. “And once we described what we saw in our research, experimental data from the last 20 years fell into place.”