Scientists from the University of Warwick have developed a new method to view proteins that are inside of human cells using Ferritin, a large protein shell that cells use to store iron.
The researchers created FerriTag, a genetically encoded inducible paper tag that enables the cell to make the tag itself and avoid damage caused by placing the tag from outside the cell. This enables the team to view the protein inside of the cell with electron microscopy.
The researchers originally set out to localize a protein found in clathrin-coated pits—100 nanometer wide entry points used by viruses to invade cells and infect them.
Using the new FerriTag, the team was able to view exactly where the protein is found in the pit and on the inside face of the cell’s surface.
“Proteins do almost all of the jobs in cells that scientists want to study,” Stephen Royle, Ph.D., associate professor and Senior Cancer Research UK Fellow at Warwick Medical School, said. “We can learn a lot about how proteins work by simply watching them down the microscope. But we need to know their precise location.”
While light microscopy can be used to view how proteins move around, the resolution is often too low to see the protein’s precise location. However, using electron microscopy gives the researchers a higher resolution.
To allow proteins to be viewed by both microscopes and correlate them, the research team developed a method of tagging the proteins so that they can be seen by both types of equipment. Tagging is widely used and several tags are available. However, they are often not precise and do not always work on single proteins.
To overcome some of the limitations, the researchers created the new tag, that was fused with a fluorescent protein.
“When Ferritin is fused to a protein, we end up with a mush,” Royle said. “So, we altered Ferritin so that it could be attached to the protein of interest by using a drug.This meant that we could put the FerriTag onto the protein we want to image in a few seconds. The cool thing about FerriTag is that it is genetically encoded. That means that we get the cell to make the tag itself and we don’t have to put it in from outside which would damage the cell.”
The study was published in Nature Communications.