CD300LF Polymorphisms of Inbred Mouse Strains Confer Resistance to Murine Norovirus Infection in a Cell Type-Dependent Manner

Amino acid substitutions in norovirus VP1 dictate cell tropism via an attachment process dependent on membrane mobility

Viruses interact with receptors on the cell surface to initiate and co-ordinate infection. The distribution of receptors on host cells can be a key determinant of viral tropism and host infection. Unravelling the complex nature of virus-receptor interactions is, therefore, of fundamental importance to understanding viral pathogenesis. Noroviruses are non-enveloped, icosahedral, positive-sense RNA viruses of global importance to human health, with no approved vaccine or antiviral agent available. Here we use murine norovirus as a model for the study of molecular mechanisms of virus-receptor interactions. We show that variation at a single amino acid residue in the major viral capsid protein had a key impact on the interaction between virus and receptor. This variation did not affect virion production or virus growth kinetics, but a specific amino acid was rapidly selected through evolution experiments, and significantly improved cellular attachment when infecting immune cells in suspension. However, reducing plasma membrane mobility counteracted this phenotype, providing insight into for the role of membrane fluidity and receptor recruitment in norovirus cellular attachment. When the infectivity of a panel of recombinant viruses with single amino acid variations was compared in vivo, there were significant differences in the distribution of viruses in a murine model, demonstrating a role in cellular tropism in vivo. Overall, these results highlight the importance of lipid rafts and virus-induced receptor recruitment in viral infection, as well as how capsid evolution can greatly influence cellular tropism, within-host spread and pathogenicity.

Glycan Recognition in Human Norovirus Infections

Recognition of cell-surface glycans is an important step in the attachment of several viruses to susceptible host cells. The molecular basis of glycan interactions and their functional consequences are well studied for human norovirus (HuNoV), an important gastrointestinal pathogen. Histo-blood group antigens (HBGAs), a family of fucosylated carbohydrate structures that are present on the cell surface, are utilized by HuNoVs to initially bind to cells. In this review, we describe the discovery of HBGAs as genetic susceptibility factors for HuNoV infection and review biochemical and structural studies investigating HuNoV binding to different HBGA glycans. Recently, human intestinal enteroids (HIEs) were developed as a laboratory cultivation system for HuNoV. We review how the use of this novel culture system has confirmed that fucosylated HBGAs are necessary and sufficient for infection by several HuNoV strains, describe mechanisms of antibody-mediated neutralization of infection that involve blocking of HuNoV binding to HBGAs, and discuss the potential for using the HIE model to answer unresolved questions on viral interactions with HBGAs and other glycans.

Noroviruses-The State of the Art, Nearly Fifty Years after Their Initial Discovery

Human noroviruses are recognised as the major global cause of viral gastroenteritis. Here, we provide an overview of notable advances in norovirus research and provide a short recap of the novel model systems to which much of the recent progress is owed. Significant advances include an updated classification system, the description of alternative virus-like protein morphologies and capsid dynamics, and the further elucidation of the functions and roles of various viral proteins. Important milestones include new insights into cell tropism, host and microbial attachment factors and receptors, interactions with the cellular translational apparatus, and viral egress from cells. Noroviruses have been detected in previously unrecognised hosts and detection itself is facilitated by improved analytical techniques. New potential transmission routes and/or viral reservoirs have been proposed. Recent in vivo and in vitro findings have added to the understanding of host immunity in response to norovirus infection, and vaccine development has progressed to preclinical and even clinical trial testing. Ongoing development of therapeutics includes promising direct-acting small molecules and host-factor drugs.