A GFP-tagged nucleoprotein-based aggregation assay for anti-influenza drug discovery and antibody development

Influenza is a viral pandemic that affects millions of people worldwide. Seasonal variations due to genetic shuffling and antigenic drifts in the influenza viruses have necessitated continual updating of therapeutics. The growing resistance to current influenza drugs has increased demand for new antivirals. The highly conserved nature of NP, a multi-functional viral protein that is serotypically distinct and abundantly expressed during infection, has led to its use in developing universal biotherapeutics and vaccines that could be effective against the virus, irrespective of its strain variations. Compounds causing aggregation of NP have recently been shown to be potent antivirals but require the development of new high-throughput assays capable of screening compounds with similar modes of action. Here, we describe the development of a new bioassay for the Influenza A nucleoprotein (NP). The assay was developed to quantify ligand-induced aggregation of a GFP-tagged NP and was validated with aggregation-inducing compounds such as nucleozin and a NP-specific antibody. The new NP–GFP aggregation assay can be performed with partially purified or mixtures of proteins and is amenable to a high-throughput format. Using this assay, we demonstrate the potential of a new anti-NP polyclonal antibody that we have obtained from chicken. This cost-effective high-yield source of anti-NP IgY has potential for large-scale production and development of therapeutic antibodies. The simplicity, speed and flexibility of this assay make it an invaluable tool for timely development of effective antivirals that can help to control future epidemics.