Higher polymerase activity associated with epidemic potential of norovirus strains

Miranda de Graaf, Erasmus MC

Stefan T. van der Krieken1#, Nele Villabruna2#, Myra Hosmillo3, Dennis Schmitz4, Claudia M.E. Schapendonk1, Kevin Groen1, Annelies Kroneman4, Harry Vennema4, Peter A. White5, Ian G. Goodfellow3, Marion P.G. Koopmans1, Miranda de Graaf1 1 Department of Viroscience, Erasmus MC, Wytemaweg 80, 3015 CN Rotterdam, The Netherlands 2 Institute for Biochemistry & Research Center for Emerging Infections and Zoonoses, University of Veterinary Medicine Hannover, Hannover, Germany 3 Division of Virology, Department of Pathology, University of Cambridge, Cambridge, UK 4 National Institute for Public Health and the Environment (RIVM), Bilthoven, The Netherlands 5 School of Biotechnology and Biomolecular Sciences, Faculty of Science, University of New South Wales, Sydney, NSW 2052, Australia. # These authors contributed equally

Entry and Replication

Noroviruses are a leading cause of acute gastroenteritis. The last two decades have been predominated by genotype GII.4 viruses, which have evolved through antigenic drift. However, during the winter of 2016, GII.4 and GII.2 recombined with a novel GII.P16 RNA dependent RNA polymerase (RdRp) and replaced the parent strains. The capsids of these GII.4- and GII.2-GII.P16 recombinants were not antigenically distinct from their predecessors, suggesting a mechanism of fitness gain other than antigenic drift. One hypothesis is that specific mutations in the GII.P16 RdRp have led to increased activity of the polymerase, resulting in higher viral loads that eventually lead to displacement of circulating strains
In this study, we compared the RdRp activity of GII.P16 RdRps from frequently and sporadically detected recombinant noroviruses using both a luciferase reporter cell-based assay and a cell-free system. Post-2016 GII.P16 RdRps demonstrated higher RdRp activity than those circulating before 2016. Mutation analysis revealed that three of five unique substitutions in the new GII.P16 RdRp, located near conserved motifs, significantly enhanced activity. Additionally, the addition of capsid proteins further increased RdRp activity, with a more pronounced effect for epidemic GII.P16 RdRps compared to earlier lineages and sporadic strains.
These findings highlight differences in RdRp activity that may contribute to norovirus emergence and suggest that, alongside capsid evolution, changes in nonstructural proteins like RdRp may role in the epidemiological success of emerging recombinant noroviruses.