Fucose Binding Cancels out Mechanical Differences between Distinct Human Noroviruses.

The majority of nonbacterial gastroenteritis in humans and livestock is caused by noroviruses. Like most RNA viruses, frequent mutations result in various norovirus variants. The strain-dependent binding profiles of noroviruses to fucose are supposed to facilitate norovirus infection. It remains unclear, however, what the molecular mechanism behind strain-dependent functioning is. In this study, by applying atomic force microscopy (AFM) nanoindentation technology, we studied norovirus-like particles (noroVLPs) of three distinct human norovirus variants. We found differences in viral mechanical properties even between the norovirus variants from the same genogroup. The noroVLPs were then subjected to fucose treatment. Surprisingly, after fucose treatment, the previously found considerable differences in viral mechanical properties among these variants were diminished. We attribute a dynamic switch of the norovirus P domain upon fucose binding to the reduced differences in viral mechanical properties across the tested norovirus variants. These findings shed light on the mechanisms used by norovirus capsids to adapt to environmental changes and, possibly, increase cell infection. Hereby, a new step towards connecting viral mechanical properties to viral prevalence is taken.

N-terminal VP1 Truncations Favor T = 1 Norovirus-Like Particles.

Noroviruses cause immense sporadic gastroenteritis outbreaks worldwide. Emerging genotypes, which are divided based on the sequence of the major capsid protein VP1, further enhance this public threat. Self-assembling properties of the human norovirus major capsid protein VP1 are crucial for using virus-like particles (VLPs) for vaccine development. However, there is no vaccine available yet. Here, VLPs from different variants produced in insect cells were characterized in detail using a set of biophysical and structural tools. We used native mass spectrometry, gas-phase electrophoretic mobility molecular analysis, and proteomics to get clear insights into particle size, structure, and composition, as well as stability. Generally, noroviruses have been known to form mainly T = 3 particles. Importantly, we identified a major truncation in the capsid proteins as a likely cause for the formation of T = 1 particles. For vaccine development, particle production needs to be a reproducible, reliable process. Understanding the underlying processes in capsid size variation will help to produce particles of a defined capsid size presenting antigens consistent with intact virions. Next to vaccine production itself, this would be immensely beneficial for bio-/nano-technological approaches using viral particles as carriers or triggers for immunological reactions.

Comparative pathogenesis of Ebola virus and Reston virus infection in humanized mice.

Filoviruses of the genus Ebolavirus include 6 species with marked differences in their ability to cause disease in humans. From the highly virulent Ebola virus to the seemingly nonpathogenic Reston virus, case fatality rates can range between 0% and 90%. In order to understand the molecular basis of these differences, it is imperative to establish disease models that recapitulate human disease as faithfully as possible. Nonhuman primates (NHPs) are the gold-standard models for filovirus pathogenesis, but comparative studies are skewed by the fact that Reston virus infection can be lethal for NHPs. Here we used HLA-A2-transgenic, NOD-scid-IL-2γ receptor-knockout (NSG-A2) mice reconstituted with human hematopoiesis to compare Ebola virus and Reston virus pathogenesis in a human-like environment. While markedly less pathogenic than Ebola virus, Reston virus killed 20% of infected mice, a finding that was linked to exacerbated inflammation and viral replication in the liver. In addition, the case fatality ratios of different Ebolavirus species in humans were recapitulated in the humanized mice. Our findings point to humanized mice as a putative model to test the pathogenicity of newly discovered filoviruses, and suggest that further investigations on Reston virus pathogenesis in humans are warranted.