Structural biology is undergoing a seismic shift as single-particle cryo-electron microscopy (cryo-EM) is increasingly becoming the technique of choice for scientists who want to study DNA, proteins and other biological molecules at atomic resolution.
Having just recently broken the 3 Å (angstrom) barrier with the use of the Gatan K2 Summit® direct detection camera, a new structure shows that there is no longer a resolution gap between x-ray crystallography and cryo-EM.
This recent work, spearheaded by Dr. Sriram Subramaniam, senior investigator at the National Cancer Institute, a part of the National Institutes of Health, describes the 2.2 Å structure of a small protein in complex with an inhibitor which blocks its function. 2.2 Å resolution cryo-EM structure of β-galactosidase in complex with a cell-permeant inhibitor.
The researchers show in their new work that they can achieve resolutions that are good enough to almost visualize the atoms in individual amino acid residues in proteins. Dr. Subramaniam notes that the quality of the map is high enough to resolve “holes” at the center of tryptophan and phenylalanine residues, a feature typically associated with structures derived by x-ray crystallography at resolutions better than ~2 Å resolution.
This particular result was achieved using the Gatan GIF Quantum LS® imaging filter with the Gatan K2 Summit electron counting direct detection camera.
“In much the way a glass prism separates wavelengths of light, the GIF Quantum LS selects only those electrons that will meaningfully contribute to the quality of an image” explains Christopher Booth, Life Science Product Manager at Gatan. “By using the K2 Summit camera with the Quantum LS energy filter, scientists are able to collect images of very delicate biological materials with the highest contrast and resolution possible.”
“This result has very large implications for drug design,” says Sander Gubbens, President of Gatan. “The advantage of cryo-EM has always been the simplicity from which you can go from a sample in a test tube to a specimen in a microscope. Now that this technique allows you to see water molecules, ions and ligands in a protein without the need for crystallization, it means that many more biological molecules can be studied at an atomic level. Since an atomic resolution structure is the key first step in rational drug design; we are entering an exciting time in for drug discovery.”
Cryo-EM is emerging as a major tool in a structural biologist’s arsenal, alongside conventional x-ray crystallography and NMR techniques, to study molecular interactions in supramolecular assemblies or biological machines.
Cryo-EM enables structure-based examination of native and hydrated biological complexes such as viruses, small organelles, and macromolecular biological complexes of 150 kDa or larger. Compared to conventional techniques, single-particle cryo-EM can provide resolutions approaching 2 Å for stable samples and allows you to obtain meaningful results with samples that are heterogeneous, metastable and extremely difficult to crystalize.
For more information regarding the GIF Quantum LS imaging filter, please visit: http://www.gatan.com/quantumls