Cryo-EM Reveals Architectural Diversity in Active Rotavirus Particles

Flexible, disposable photocatalytic plastic films for the destruction of viruses

A thin, 30 μm, flexible, robust low-density polyethylene, LDPE, film, loaded with 30 wt% P25 TiO₂, is extruded and subsequently rendered highly active photocatalytically by exposing it to UVA (352 nm, 1.5 mW cm⁻²) for 144 h. The film was tested for anti-viral activity using four different viruses, namely, two strains of Influenza A Virus (IAV), WSN, and a recombinant PR8, encephalomyocarditis virus (EMCV), and SARS-CoV-2 (SARS2). The film was irradiated with either UVA radiation (352 nm, 1.5 mW cm⁻²; although only 0.25 mW cm⁻² for SARS2) or with light from a cool white fluorescent lamp (UVA irradiance: 365 nm, 0.047 mW cm⁻²). In all cases the films exhibited an average virus inactivation rate of >1.5log/h. In the case of SARS2, the rates were > 2log/h, with the rate determined using a dedicated, low intensity UVA source (0.25 mW cm⁻²) only 1.3 x's faster than that for a cool white lamp (UVA irradiance = 0.047 mW cm⁻²), which suggests that SARS2 is particularly prone to photocatalytic inactivation even under low UV irradiation conditions, such as found in a room lit with just white fluorescent tubes. This is the first example of a flexible, very thin, photocatalytic plastic film, produced by a scalable process (extrusion), for virus inactivation. The potential of such a film for use as a disposable, self-sterilising thin plastic material alternative to the common, non-photocatalytic, inert equivalent used currently for curtains, aprons and table coverings in healthcare is discussed briefly.

Mature Rotavirus Particles Contain Equivalent Amounts of 7meGpppG-Capped and Noncapped Viral Positive-Sense RNAs

Viruses have evolved different strategies to overcome their recognition by the host innate immune system. The addition of caps at their 5' RNA ends is an efficient mechanism not only to ensure escape from detection by the innate immune system but also to ensure the efficient synthesis of viral proteins. Rotavirus mRNAs contain a type 1 cap structure at their 5' end that is added by the viral capping enzyme VP3, which is a multifunctional protein with all the enzymatic activities necessary to add the cap and also functions as an antagonist of the 2'-5'-oligoadenylate synthetase (OAS)/RNase L pathway. Here, the relative abundances of capped and noncapped viral RNAs during the replication cycle of rotavirus were determined. We found that both classes of rotaviral plus-sense RNAs (+RNAs) were encapsidated and that they were present in a 1:1 ratio in the mature infectious particles. The capping of viral +RNAs was dynamic, since different ratios of capped and noncapped RNAs were detected at different times postinfection. Similarly, when the relative amounts of capped and uncapped viral +RNAs produced in an in vitro transcription system were determined, we found that the proportions were very similar to those in the mature viral particles and in infected cells, suggesting that the capping efficiency of VP3, both in vivo and in vitro, might be close to 50%. Unexpectedly, when the effect of simultaneously knocking down the expression of VP3 and RNase L on the cap status of viral +RNAs was evaluated, we found that, even though at late times postinfection there was an increased proportion of capped viral RNAs in infected cells, the viral particles isolated from this condition contained equal ratios of capped and noncapped viral RNA, suggesting that there might be selective packaging of capped and noncapped RNAs. IMPORTANCE Rotaviruses have a genome composed of 11 segments of double-stranded RNA. Whether all 5' ends of the positive-sense genomic RNAs contained in the mature viral particles are modified by a cap structure is unknown. In this work, we characterized the relative proportions of capped and noncapped viral RNAs in rotavirus-infected cells and in viral particles by using a direct quantitative assay. We found that, independent of the relative proportions of capped/noncapped RNAs present in rotavirus-infected cells, there were similar proportions of these two kinds of 5'-modified positive-sense RNAs in the viral particles.

Graphene Oxide-Supported Microwell Grids for Preparing Cryo-EM Samples with Controlled Ice Thickness

Cryogenic-electron microscopy (cryo-EM) is the preferred method to determine 3D structures of proteins and to study diverse material systems that intrinsically have radiation or air sensitivity. Current cryo-EM sample preparation methods provide limited control over the sample quality, which limits the efficiency and high throughput of 3D structure analysis. This is partly because it is difficult to control the thickness of the vitreous ice that embeds specimens, in the range of nanoscale, depending on the size and type of materials of interest. Thus, there is a need for fine regulation of the thickness of vitreous ice to deliver consistent high signal-to-noise ratios for low-contrast biological specimens. Herein, an advanced silicon-chip-based device is developed which has a regular array of micropatterned holes with a graphene oxide (GO) window on freestanding silicon nitride (Six Ny ). Accurately regulated depths of micropatterned holes enable precise control of vitreous ice thickness. Furthermore, GO window with affinity for biomolecules can facilitate concentration of the sample molecules at a higher level. Incorporation of micropatterned chips with a GO window enhances cryo-EM imaging for various nanoscale biological samples including human immunodeficiency viral particles, groEL tetradecamers, apoferritin octahedral, aldolase homotetramer complexes, and tau filaments, as well as inorganic materials.

High-Resolution Imaging of Human Viruses in Liquid Droplets

Liquid-phase electron microscopy (LP-EM) is an exciting new area in the materials imaging field, providing unprecedented views of molecular processes. Time-resolved insights from LP-EM studies are a strong complement to the remarkable results achievable with other high-resolution techniques. Here, the opportunities to expand LP-EM technology beyond 2D temporal assessments and into the 3D regime are described. The results show new structures and dynamic insights of human viruses contained in minute volumes of liquid while acquired in a rapid timeframe. To develop this strategy, adeno-associated virus (AAV) is used as a model system. AAV is a well-known gene therapy vehicle with current applications involving drug delivery and vaccine development for COVID-19. Improving the understanding of the physical properties of biological entities in a liquid state, as maintained in the human body, has broad societal implications for human health and disease.