Correlative light and electron microscopy image of the protein dynamin (magenta) at endocytic structures (grey honeycomb lattice) of a mammalian cell.
Credit: Kem Sochacki, Ph.D. NHLBI, DIR

New Frontiers in Imaging: An explosion in the use of CryoEM is changing how scientists work

Every day researchers across NIH use an array of imaging technologies and equipment to help them make new scientific discoveries. However, over the last 10-15 years, a massive explosion in the use of Cryo-Electron Microscopy (cryo-EM) – a technique that allows the direct imaging of proteins within cells – has revolutionized the way scientists do their work.

Now NIH and institutions around the globe are racing to invest in cryo-EM technology, said Justin Taraska, Ph.D., chief of NHLBI’s molecular and cellular imaging laboratory. “We can see things now that we were never able to see before,” he said, “and this has opened up all kinds of possibilities for discovering the causes of human disease, and even treating them.”

At NIH the increased investment in cryo-EM has led to the consolidation and expansion of this innovative technology across the campus, said Jenny Hinshaw, Ph.D., who is leading the collaborative effort. Hinshaw, a structural biologist at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), now oversees what’s known as the Multi-Institute cryo-EM Facility (NIH MICEF), where several large cryo-EM microscopes are housed.

“In a very short period, labs across campus have begun using the MICEF facilities to do cutting edge work in cryo-EM,” Hinshaw said. The groundbreaking technique, she noted, has helped researchers understand the structures of more than 80 proteins each year, and that has been critical to learning about how disease develops.

Although cryo-EM has been around for some time, the development of special cameras, microscopes, and computational tools have helped make the technique a lot more accessible to scientists. With cryo-EM, Hinshaw explained, researchers can now see a 3D view of cells right in their native environment by flash freezing the samples at very low (cryogenic) temperatures. They then use a specialized electron microscope to take an image of those cells. This method, for example, has been key to understanding the structure of SARS-CoV-2, the virus that causes COVID-19, and has led to clues for future vaccine development, Hinshaw noted.

Electron microscope image of the inner membrane of a mammalian cell.
Platinum replica electron microscope image of the inner membrane of a mammalian cell. Source: Justin Taraska, Ph.D., chief of NHLBI’s molecular and cellular imaging laboratory

Recently, the MICEF team expanded its work and added some new technology – focused ion beam milling, which allows scientists to cut into cells and view very thin pieces of cell contents; and cryogenic fluorescence, which helps them locate and find specific proteins.

“For rare or diseased proteins, in the past it was a bit like finding a needle in a haystack,” Taraska said. “With fluorescence, the needle – or in this case, the protein – glows. And this allows us to visualize how the protein is shaped.”

In recent months, thanks to additional funding, cryo-EM research on the NIH campus has expanded even further. The Chan Zuckerberg Initiative, a philanthropy focused on science, education, and justice and opportunity, awarded nearly $28 million to support visualizing the structures of all human proteins inside cells. Taraska, Hinshaw, and Naoko Mizuno, Ph.D., chief of NHLBI’s structural cell biology laboratory, received funding to build upon technology they are developing that would allow unprecedented views of the structure, quantity, distribution, and interactions of proteins inside cells.

The scientists and their teams are using their expertise in fluorescence, electron microscopy, and solving protein structures to develop new techniques that will better visualize proteins at the plasma membrane, which is the gateway to the cell. Most drugs target receptors at the plasma membrane, and many must also cross this barrier to enter the cells to do their work. The plasma membrane, however, has been difficult to study with cryo-EM, and the three groups are working to make that more possible.

“This is the future of imaging,” Mizuno noted. “By streamlining this approach, we are making it easier for researchers to not only see cells with higher resolution, but learn how they specifically function and move within these states.”

Robert Balaban, M.D., NHLBI’s scientific director, agreed. “The cryo-EM approach being developed give us unprecedented insight into the structure and function of proteins inside of the cells,” he said. “This is challenging many old dogmas of how proteins work and raising questions we will be addressing in the next several decades.”