Biological Nano-Machines at Atomic Resolution: Single-Particle Cryo-EM

Reference Presenter Authors
Marin Van Heel Heel, M.V.(LNNano-CNPEM Campinas / Leiden University / Imperial College London); Molecular nano-machines – better known as macromolecular complexes – perform most biological processes in all walks of life. In recent years electron microscopy has gone through a “resolution revolution” which has made cryogenic electron microscopy to a technique capable of elucidating the three-dimensional (3D) structure of large macromolecular complexes with an ever-improving level of detail. In favourable cases, a de-novo structure determination by cryo-EM alone has proved feasible. The resolution levels achieved in determining the structure of the bacterial ribosome, for example, exceeds that achieved by conventional X-ray crystallography. At the resolution level of ~3Å, cryo-EM reaches an important threshold: we start seeing the side chains of proteins allowing for a better insight in their functioning. The Nobel Prize for Chemistry 2017 was awarded for cryo-EM in recognition of the decades of developments that led to this 4D visualisation revolution. The most challenging developments in cryo-EM are the visualization of local effects in the nano-structures one studies. The achieved “results resolution” in the 3D reconstructions is mostly limited by the sample and the data processing, rather than by the maximum possible “instrumental resolution”. At the same time, the results-resolution changes from place to place within the structure: different parts of the object may be imaged with different resolution levels. The concept of “local resolution” and its visualisation comes to play here. Last but not least, the concept of local “cross resolution” between two very similar objects may turn out to be of crucial importance when interpreting the results in the biological and material sciences alike.
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