New cryo-EM technology at St. Jude Children’s Research Hospital pushes boundaries of molecular imaging

For decades, structural biologists have sought to map the structures of proteins and other macromolecules within cells. Cryo-electron microscopy (cryo-EM), whose early development traces back to the 1970s, emerged as a promising technique for visualizing cells in their natural, hydrated state. But the technology’s initial inability to produce sharp images was a stumbling block in the early days. Early cryo-electron microscopes, while still a breakthrough, produced images so blurry that the field earned the self-deprecating nickname “blob-ology.” It wasn’t until around 2012 that advances in detectors and image processing software propelled cryo-EM to widespread popularity and recognition, ushering in a “resolution revolution,” as Science put it in 2017.

Pushing resolution boundaries

Now, Liz Kellogg, Ph.D., Associate Member in the Department of Structural Biology at St. Jude Children’s Research Hospital, is among a select group of researchers with access to a new cryo-EM instrument capable of pushing the resolution boundaries further. “In terms of cryo-EM in the U.S., there might be two other institutions that have similar setups,” Kellogg adds. “And what’s so special about this setup is that it is able to generate atomic-resolution structures and will be great to push our cryo-ET efforts.” [Learn more about St. Jude’s gene editing research here.]

Cryo-electron tomography (cryo-ET) is a specialized form of cryo-electron microscopy that allows scientists to visualize the 3D structure of biological samples, like cells or tissues, in their natural environment. The technique involves rapidly freezing the sample to preserve its structure and then imaging it from multiple angles via an electron microscope. These images are then combined computationally to create a detailed 3D model.

The new cryo-EM microscope, part of the St. Jude Cryo-Electron Microscopy and Tomography Center, is a Titan Krios G4 equipped with a cold FEG electron source, a SelectrisX energy filter, and a Falcon 4i camera. The cold FEG electron source optimizes beam coherence and brightness, enabling exceptionally high-resolution imaging. The energy filter improves enhanced contrast and the signal-to-noise ratio in acquired images. The Falcon 4i camera supports rapid, high-sensitivity electron detection and crisp image quality at both high and low magnifications.

“All of these elements come together to produce high-quality, detailed images,” Kellogg explained. “This is a highly customized setup that represents a significant investment.”

Down to the atomic level

“This new microscope can achieve resolutions down to 1.2 angstroms (Å),” Kellogg said. To put that into perspective, that’s essentially the resolution scale of X-ray crystallography, a technique that enables scientists to see the separation between atoms.

“At this level of resolution, we can see the atomic arrangements that allow molecules to execute their biological functions,” Kellogg said. “We can also observe exactly how a small molecule binds to specific sites in a macromolecule, which is essential for drug discovery.”

Inside the advanced electron microscopy facility at St. Jude

The Titan Krios G4 microscope’s ability to achieve resolutions as high as 1.2 angstroms opens up new possibilities for understanding the workings of biological systems. “To understand a biological process in detail, we need to be able to see how it happens with precision” Kellogg said. Researchers are now able to see how individual atoms are arranged within a protein, how a water molecule nestles between a protein and DNA, and how a drug molecule fits into its target binding pocket. “I know a lot of people at St. Jude are interested in looking at drug interactions,” Kellogg said. “And to drive drug discovery, you really need that level of precision to observe how a small molecule binds to its target.”

At St. Jude, the availability of powerful tools such as the new cryo-EM microscope is also a factor attracting other researchers aimed to help tackle severe pediatric diseases. “I think we have a absolutely fantastic group of talented, passionate scientists,” Kellogg explained. “And everybody is motivated by our shared mission to cure fatal childhood diseases.”