Tagging method gives new view of proteins inside our cells

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Scientists have created a new way to view proteins inside human cells.

The researchers’ method allows an electron microscope to view proteins precisely, unlike current methods. They named the new technique FerriTag because it is based on ferritin, which an electron microscope can view because iron scatters electrons. Ferritin is a large protein shell that our cells use to store iron.

The team set out to precisely locate a protein found in clathrin-coated pits. These are 100 nm-wide entry points viruses use to invade and infect cells. Using FerriTag, the team could see 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. We can learn a lot about how proteins work by simply watching them down the microscope. But we need to know their precise location,” says Stephen Royle, associate professor and senior cancer research UK fellow at the University of Warwick Medical School and leader of the research team.

Although light microscopy can be used to see proteins move around, the resolution is low, so seeing a protein’s precise location is impossible. Electron microscopy, which gives a higher resolution, can overcome this limitation.

To view proteins by both microscopes and correlate them, the researchers developed a method of tagging the proteins. Tagging is widely used and several tags are available, though they have established drawbacks. Some are not precise enough, or they don’t work on single proteins. To overcome this, Royle’s lab created a new tag and fused it with a fluorescent protein.

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Royle says his lab had to defeat another obstacle, as well: “When Ferritin is fused to a protein, we end up with a mush. 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,” Royle explains.

The research appears in the journal Nature Communications.

Source: University of Warwick