Towards an optimum design for electrostatic phase plates

Forty years in cryoEM of membrane proteins

In a surprisingly short time, electron cryo-microscopy (cryoEM) has developed from a niche technique in structural biology to a mainstream method practiced in a rapidly growing number of laboratories around the world. From its beginnings about 40 years ago, cryoEM has had a major impact on the study of membrane proteins, in particular the energy-converting systems from bacterial, mitochondrial and chloroplast membranes. Early work on two-dimensional crystals attained resolutions ∼3.5 Å, but at present, single-particle cryoEM delivers much more detailed structures without crystals. Electron cryo-tomography of membranes and membrane-associated proteins adds valuable context, usually at lower resolution. The review ends with a brief outlook on future prospects.

Comparative image simulations for phase-plate transmission electron microscopy

Numerous physical phase plates (PP) for phase-contrast enhancement in transmission electron microscopy (TEM) have been proposed and studied with the hole-free or Volta PP having a high impact and interest in recent years. This study is concerned with comparative TEM image simulations considering realistic descriptions of various PP approaches and samples from three different fields of application covering a large range of object sizes. The simulated images provide an illustrative characterization of the typical image appearance and common artifacts of the different PPs and the influence of simulation parameters especially important for PP simulations. A quantitative contrast analysis shows the superior phase-shifting properties of the hole-free phase plate for biological applications and the benefits of adjustable phase plates. The application of PPs in high-resolution TEM imaging, especially of weak-phase objects such as (atomically thin) 2D materials, is shown to increase image interpretability. The software with graphical user interface written and used for the presented simulations is available for free usage.

Setup and Troubleshooting of Volta Phase Plate Cryo-EM Data Collection

Cryo electron microscopy (cryo-EM) has become a method of choice in structural biology to analyze isolated complexes and cellular structures. This implies adequate imaging of the specimen and advanced image-processing methods to obtain high-resolution 3D reconstructions. The use of a Volta phase plate in cryo-EM drastically increases the image contrast while being able to record images at high acceleration voltage and close to focus, i.e., at conditions where high-resolution information is best preserved. During image processing, higher contrast images can be aligned and classified better than lower quality ones resulting in increased data quality and the need for less data. Here, we give step-by-step guidelines on how to set up high-quality VPP cryo-EM single particle data collections, as exemplified by human ribosome data acquired during a one-day data collection session. Further, we describe specific technical details in image processing that differ from conventional single particle cryo-EM data analysis.

Phase plates in the transmission electron microscope: operating principles and applications

In this paper, we review the current state of phase plate imaging in a transmission electron microscope. We focus especially on the hole-free phase plate design, also referred to as the Volta phase plate. We discuss the implementation, operating principles and applications of phase plate imaging. We provide an imaging theory that accounts for inelastic scattering in both the sample and in the hole-free phase plate.

How Good Can Single-Particle Cryo-EM Become? What Remains Before It Approaches Its Physical Limits?

Impressive though the achievements of single-particle cryo-electron microscopy are today, a substantial gap still remains between what is currently accomplished and what is theoretically possible. As is reviewed here, twofold or more improvements are possible as regards (a) the detective quantum efficiency of cameras at high resolution, (b) converting phase modulations to intensity modulations in the image, and (c) recovering the full amount of high-resolution signal in the presence of beam-induced motion of the specimen. In addition, potential for improvement is reviewed for other topics such as optimal choice of electron energy, use of aberration correctors, and quantum metrology. With the help of such improvements, it does not seem to be too much to imagine that determining the structural basis for every aspect of catalytic control, signaling, and regulation, in any type of cell of interest, could easily be accelerated fivefold or more.

The integrative role of cryo electron microscopy in molecular and cellular structural biology

After gradually moving away from preparation methods prone to artefacts such as plastic embedding and negative staining for cell sections and single particles, the field of cryo electron microscopy (cryo-EM) is now heading off at unprecedented speed towards high-resolution analysis of biological objects of various sizes. This 'revolution in resolution' is happening largely thanks to new developments of new-generation cameras used for recording the images in the cryo electron microscope which have much increased sensitivity being based on complementary metal oxide semiconductor devices. Combined with advanced image processing and 3D reconstruction, the cryo-EM analysis of nucleoprotein complexes can provide unprecedented insights at molecular and atomic levels and address regulatory mechanisms in the cell. These advances reinforce the integrative role of cryo-EM in synergy with other methods such as X-ray crystallography, fluorescence imaging or focussed-ion beam milling as exemplified here by some recent studies from our laboratory on ribosomes, viruses, chromatin and nuclear receptors. Such multi-scale and multi-resolution approaches allow integrating molecular and cellular levels when applied to purified or in situ macromolecular complexes, thus illustrating the trend of the field towards cellular structural biology.

CryoEM at IUCrJ: a new era

In this overview, we briefly outline recent advances in electron cryomicroscopy (cryoEM) and explain why the journal IUCrJ, published by the International Union of Crystallography, could provide a natural home for publications covering many present and future developments in the cryoEM field.