Cryo-electron microscopy reveals the molecular details of ephephritin, an iron, spherical protein complex that stores iron.
Paul Emsley / MRC Laboratory of Molecular Biology
By Robert F. Service
If you want to map the smallest parts of a protein, you only have a few options: you can coax millions of individual protein molecules to organize into crystals and analyze them using X-ray crystallization. Or you can flash-freeze copies of proteins and bombard them with electrons, a low-resolution method called cryo-electron microscopy (cryo-EM). Now, for the first time, scientists have sharpened the resolution of cryo-EM at the molecular level so that they can direct the position of individual molecules in different proteins in the resolution of the competitors of X-ray crystallography.
“This is just amazing,” says Melanie Ohi, a cryo-EM expert at the University of Michigan, Ann Arbor. “To see this level of detail, it’s just beautiful.” Because sharp resolutions show how complex cellular machines do their job, improvements in cryo-EM should gain numerous new insights into biology into science.
To map protein structures, scientists have been using X-ray crystallization since the late 1950s. By bombarding the crystallized protein with X-rays and analyzing how to turn off the X-ray ricochet, scientists can create the possible composition and shape of the protein. Decades of improvements in X-ray beams, detectors and computer power have made the approach faster and more accurate. The approach does not work well when the proteins are exceptionally large, working in complexes such as ribosomes, or cannot be crystallized, as are many proteins that sit in the cell membrane.
In contrast, the researchers used cryo-EM fire electrons on copies of stable proteins that did not require crystallization; Detectors record the defects of the electrons, and the sophisticated software stitches the images together to work out the protein’s makeup and shape. Researchers in Japan have previously shown that they can narrow the resolution to 1.54 anglers – they do not reach the point where they can isolate individual molecules – in an intestinal protein called eopheritin, which binds and stores iron. Now, with the help of electron beam technology detect G, detectors and software improvements, two groups of researchers from the United Kingdom and Germany have narrowed it down to whether it is sharp enough, 1.25 angstroms or better, to function the condition of individual atoms, reports today. Nature.
Advanced resolution can accelerate the already ongoing cryo-EM mutation among structural biologists. For now, the technique only works with proteins that are unusually hard. Next, the researchers will try to achieve a similarly intense resolution, such as less rigid, larger protein complexes, such as splicisomes, a larger complex of proteins and RNA molecules that cut “interns” from RNA to be converted into proteins.
