The key protein mutated in patients with Charcot-Marie-Tooth (CMT) disease type 2Y works to break down cellular complexes via a sort of “hand over hand” mechanism, a study found. The newly identified structure of the p97 protein may help in determining new targets for possible therapies, its researchers added.
The study, “Structure of the Cdc48 segregase in the act of unfolding an authentic substrate,” was published in the journal Science.
Cdc48, or p97 in humans, is responsible for unfolding protein complexes and other cellular targets, important to processes such as protein quality control.
“Cdc48 is the Swiss army knife of the cell and can interact with so many different substrates,” Peter Shen, PhD, the study’s senior author and a professor at University of Utah Health, said in a press release.
Point mutations in p97 — alterations in only one nucleotide, the building blocks of DNA and RNA — have been associated with diseases such as CMT type 2Y and amyotrophic lateral sclerosis. This protein is also an established target in ongoing cancer research.
Aiming to better understand how Cdc48/p97 works, the scientists first extracted Cdc48 from yeast cells. Then, they used an approach called cryogenic electron microscopy (cryo-EM) to take snapshots of the purified particles in different arrangements.
“Because this method is so fast, we have captured Cdc48 in the act of unfolding a protein substrate,” Shen said.
The team found that Cdc48 unfolds its substrates by adopting a helix-like configuration and passing them through a central pore via a “hand-over-hand” mechanism. This requires six protein subunits (A-F) arranged in two rings (D1 and D2), and was revealed through the use of a protein analysis technique known as applied mass spectrometry proteomics at Brigham Young University.
“The coolest part is this [work] demonstrates that we can take a protein directly out of host cells and image them in their native state,” Shen said. “I think this is the future of the cryo-EM field.”
As Cdc48 interacts with several partners almost simultaneously, the team was unable to visualize the entire complex. This protein’s ability to multi-task will continue being studied by the researchers.
As Cdc48 in yeast closely resembles p97 in humans, these findings may have broader implications. “We believe the structure we solved here will look very similar to what our bodies are expressing right now,” Shan said.
“Future priorities include determining the mechanism of substrate engagement and translocation” to understand how mutations in p97 affect its function, “and leveraging the new structural insights in the development of Cdc48/p97 inhibitors that have potential as therapeutic agents,” the team wrote.