Single-particle cryo-EM-How did it get here and where will it go

Abstract

Cryo-electron microscopy, or simply cryo-EM, refers mainly to three very different yet closely related techniques: electron crystallography, single-particle cryo-EM, and electron cryotomography. In the past few years, single-particle cryo-EM in particular has triggered a revolution in structural biology and has become a newly dominant discipline. This Review examines the fascinating story of its start and evolution over the past 40-plus years, delves into how and why the recent technological advances have been so groundbreaking, and briefly considers where the technique may be headed in the future.

Figure 1.. Establishing of single particle cryo-EM

A. An electron diffraction pattern of frozen hydrated catalase crystal (9). The diffraction spots are visible at beyond 3 Å resolution. This experiment established the concept of cryo-EM. B. An electron micrograph of frozen hydrated adenovirus particle recorded from a frozen hydrated grid prepared by plunge freezing. The micrograph is from the same dataset described in (11) and reproduced from (9). C. The first 3D reconstruction of bacteriorhodopsin determined by electron crystallography (15). D. A 3D model of the 50S ribosome subunit determined by single particle reconstruction of negatively stained large ribosomal subunit from Escherichia coli (22).

Figure 2.. Direct electron detection camera enabled atomic structure determination

A. Comparison of DQE curves of a scintillator based CCD camera (black), and direct electron detection camera K2 operating in base mode (blue) and super-resolution counting mode (red) (31). B. A typical electron micrograph of archaeal 20S proteasome (~700kDa in molecular weight) recorded using direct electron detection camera (60). C. Fourier power spectrum calculated from the image (B) (60). High-resolution signal at ~3Å resolution is clearly visible (60). D. A portion of density map from the 3D reconstruction of archaeel 20S proteasome (31).

Figure 3.. Single particle cryo-EM enables atomic structure determination of TRP channels

Ribbon diagrams of atomic structures from each subfamily of TRP channel superfamily. They are TRPV1 (49), TRPA1 (61), TRPM4 (62), TRPC4 (63), NOMOPC (also named TRPN1) (64), PKD2 (or TRPP2) (65) and TRPML (66). The rapid pace of integral membrane protein structure determination is enabled by single particle cryo-EM and is unprecedented.