Biochemical maps have long been filled with blank spaces because available technology has had difficulty generating images of complex molecular machinery. But with cryo-EM, researchers can now freeze biomolecules mid-movement and visualize processes previously unseen, a decisive step for both the basic understanding of life’s chemistry and for the development of pharmaceuticals.
Henderson says that cryo-EM is in many ways just another method of discerning the structure of a molecule. “But the difference,” he emphasizes, “is there are quite a lot of structures in biology that are resistant, are recalcitrant to the other methods, like X-ray crystallography or nuclear magnetic resonance spectroscopy. So it has opened up essentially a kind of new, previously unapproachable area of structural biology.”Electron microscopes were long believed by researchers to be suitable only for the imaging of dead matter as the powerful electron beam destroys biological material. But in 1990, Henderson’s research at the MRC Laboratory of Molecular Biology at Cambridge showed electron microscopes could be used to generate a 3-D image of a protein at atomic resolution, a breakthrough that proved the technology’s potential.
The journey to Henderson’s discovery is encapsulated in the work of his fellow awardees. Frank made the technology generally applicable with his research at Columbia University. Between 1975 and 1986 he developed an image processing method in which the electron microscope’s fuzzy 2-D images were analyzed and merged to reveal a sharp 3-D structure. The process, he says, involved two steps. “One was to find relative orientations between the molecules, which is difficult if you don’t know the structure…and the other one is putting all that information together once you know the angles. These are essentially different moments, so in terms of how to find the orientations there was an aha moment in 1977 or something like this where I conceived of the random conical method.”
Dubochet added water to electron microscopy in his research at the University of Lausanne in Switzerland. Liquid water generally evaporates in an electron microscope’s vacuum, making the biomolecules collapse. But in the early 1980s, Dubochet succeeded in vitrifying water, cooling it so rapidly that it solidified in its liquid form around a biological sample, allowing the biomolecules to retain their natural shape even in a vacuum.
Following these discoveries, researchers worldwide have further optimized the method, and in 2013 reached the current atomic resolution. Researchers can now routinely produce 3-D structures of biomolecules and over the past few years, for example, have examined everything from the proteins that cause antibiotic resistance to the surface of the Zika virus. ■