Progress in spatial resolution of structural analysis by cryo-EM

Since the Human Genome Project, drug discovery via structure-based drug design and development has significantly accelerated. Therefore, generating high-resolution structural information from biological macromolecules and macromolecular complexes, such as proteins and nucleic acids, is paramount in structural biology, medicine and the pharmaceutical industry. Recently, electron cryomicroscopy (cryo-EM) has undergone a technological revolution and attracted much attention in the structure-based drug discovery pipeline. This recognition is primarily due to its ability to analyze and reconstruct high-resolution structures of previously unattainable large target macromolecular complexes captured in various functional and dynamic states. Previously, cryo-EM was a niche method in the structure determination field, and research was limited to a small number of laboratories and produced low-resolution structures incomplete for detailed and unambiguous structural interpretation. However, with the development of new camera technology, software and computational algorithms that now seamlessly integrate these new developments, the achievable resolutions produced from cryo-EM-determined structures have dramatically improved. This has solidified cryo-EM as one of the main structural determination methods widely used in the field. In this review, we introduce the evolution of two essential techniques incorporated into the cryo-EM workflow-single particle analysis and tomography-focusing on achievable resolution and the technological innovations that have become indispensable tools for high-resolution reconstruction and structural analysis of biological macromolecules. Here, we also describe challenges and discuss future prospects that have fixed cryo-EM as a dominant feature in the landscape of high-resolution structure determination methods and the structure-based drug discovery pipeline.