Electron cryo-microscopy of TPPS4⋅2HCl tubes reveals a helical organisation explaining the origin of their chirality.

A widely studied achiral porphyrin, which is highly soluble in aqueous solutions (TPPS4), is shown to self-assemble into helical nanotubes. These were imaged by electron cryo-microscopy and a state-of-the-art image analysis allows building a map at ∼5 Å resolution, one of the highest obtained so far for molecular materials. The authors were able to trace the apparent symmetry breaking to existing nuclei in the "as received samples", while carefully purified samples show that both handnesses occur in equal amounts.

Automatic magnification determination of electron cryomicroscopy images using apoferritin as a standard.

Interpretation of the structural information in cryomicroscopy images recorded on film or CCD camera requires a precise knowledge of the electron microscope parameters that affect image features such as magnification and defocus. Magnification must be determined in order to combine data from different images in a three-dimensional reconstruction and to accurately scale reconstructions for fitting with atomic resolution models. A method is described for estimating the absolute magnification of an electron micrograph of a frozen-hydrated specimen using horse spleen apoferritin as a standard.

Paraxial charge compensator for electron cryomicroscopy.

We describe a multi-hole condenser aperture for the production of several electron beams in the transmission electron microscope (TEM) making it possible to simultaneously image and irradiate spatially separated regions of a specimen. When the specimen is a thin film of vitreous ice suspended over a holey carbon film, simultaneous irradiation of the adjacent carbon support with the off-axis beam compensates for some of the effects of charging in the image formed by a beam irradiating only the ice. Because the intervening region is not irradiated, charge-neutralization of frozen-hydrated specimens can occur by a through-space mechanism such as the emission of secondary electrons from a grounded carbon support film.

Structural organization of a filamentous influenza A virus.

Influenza is a lipid-enveloped, pleomorphic virus. We combine electron cryotomography and analysis of images of frozen-hydrated virions to determine the structural organization of filamentous influenza A virus. Influenza A/Udorn/72 virions are capsule-shaped or filamentous particles of highly uniform diameter.

Structural organization of Weibel-Palade bodies revealed by cryo-EM of vitrified endothelial cells.

In endothelial cells, the multifunctional blood glycoprotein von Willebrand Factor (VWF) is stored for rapid exocytic release in specialized secretory granules called Weibel-Palade bodies (WPBs). Electron cryomicroscopy at the thin periphery of whole, vitrified human umbilical vein endothelial cells (HUVECs) is used to directly image WPBs and their interaction with a 3D network of closely apposed membranous organelles, membrane tubules, and filaments. Fourier analysis of images and tomographic reconstruction show that VWF is packaged as a helix in WPBs.

Structural determinants of rotavirus subgroup specificity mapped by cryo-electron microscopy.

The rotavirus double-layered particle (DLP) is a molecular machine that transcribes 11 genomic segments of double-stranded RNA into full-length mRNA segments during viral replication. DLPs from the human Wa strain of virus, belonging to subgroup II (SG II), possess a significantly reduced level of transcriptase activity compared to bovine UK DLPs that belong to subgroup I (SG I). Cryo-electron microscopy and icosahedral image analysis was used to define the structural basis for this difference in transcriptase activity and to derive three-dimensional density maps of bovine UK and human Wa DLPs at 26 angstroms and 28 angstroms resolution, respectively.

A structural model for maturation of the hepatitis B virus core.

Hepatitis B virus, a widespread and serious human pathogen, replicates by reverse transcription of an RNA intermediate. The virus consists of an inner nucleocapsid or core, surrounded by a lipid envelope containing virally encoded surface proteins. Using electron cryomicroscopy, we compare the structures of the bacterially expressed RNA-containing core particle and the mature DNA-containing core particle extracted from virions.

An amino-terminal segment of hantavirus nucleocapsid protein presented on hepatitis B virus core particles induces a strong and highly cross-reactive antibody response in mice.

Previously, we have demonstrated that hepatitis B virus (HBV) core particles tolerate the insertion of the amino-terminal 120 amino acids (aa) of the Puumala hantavirus nucleocapsid (N) protein. Here, we demonstrate that the insertion of 120 amino-terminal aa of N proteins from highly virulent Dobrava and Hantaan hantaviruses allows the formation of chimeric core particles. These particles expose the inserted foreign protein segments, at least in part, on their surface.