After a number of years of relatively slow improvement, recent advances in cryo–electron microscopy (cryo-EM) have finally allowed structures of large macromolecules and macromolecular complexes to be determined at near-atomic resolution. Achievement of resolutions below 4 Å are extending in very different types of macromolecules, with selected examples extending up to better than 2 Å for around 350 kD protein complexes. These results not only support the incorporation of cryo-EM as a technique of choice for structural determination, but also demonstrate that the density maps are detailed enough to show water molecules, ions, and precise side-chain conformations.             

As the analysis of images provided by cryo-EM is done particle by particle, structural heterogeneity can be studied in detail, providing unprecedented insights about structural features involved in key steps of their function and regulation. The fact that cryo-EM allows the atomic resolution analysis of complexes rapidly frozen from solution, and thus under conditions closer to physiological conditions, offers a great potential of using cryo-EM and single-particle analysis to study the protein–ligand interactions and structure-based drug design, while opening new opportunities for the study of detailed protein functional mechanisms.