2019 Volume 54 Issue 2 Pages 91-97
Cryo-EM revolutionary advancement enables us to solve biological macromolecular structures up to 1.5 Å spatial resolution. This brings up new issues, which had not received much attention before. Coma and cold field emission (CFE) are representative examples of these issues. This article describes how and why coma affects cryo-EM imaging and what should be done for collection of high-quality data. Coma introduces phase shifts, which becomes larger in higher resolution and more problematic for accurate structure determination. The effect should be carefully minimized. The merit of CFE is reviewed for higher-resolution single particle cryo-EM. The CFE source produces an electron beam with high temporal-coherence, and yields contrast transfer function curves to be remarkably less attenuated at a resolution range beyond 2 Å than those from the standard thermal field emission or Schottky source. Thus, this technology should drive cryo-EM to the next stage. Many new researchers have now started using cryo-EM and I think that the imaging theory for high-resolution cryo-EM should be updated to be fitted with these situations. I describe this article for this purpose. It also includes our recent single particle reconstructions obtained with a CRYO ARM 300 electron microscope equipped with a CFE gun.