The continuously evolving Influenza A virus poses a persistent global threat of outbreak with devastating outcomes. The front-line options for treatment of emerging strains are the anti-viral neuraminidase inhibitors, Relenza™ and Tamiflu™. However, the development of resistance against these inhibitors is a growing and serious problem. The currently emerging deadly H7N9 Influenza A strain in China has rapidly developed resistance against both anti-virals after patients were treated for just 2 days1 . This highlights the urgent need to understand the basis of resistance to currently available NA inhibitors to help guide clinical options and for the development of new therapeutics in preparation for the next possible pandemic.
Expressing and purifying recombinant neuraminidase proteins from the recent Swine and Avian flu outbreaks provides a safe and efficient system for the rapid characterisation of resistance mutants. Purified protein, were shown to form stable tetramers by size exclusion chromatography and dynamic light scattering. The protein was active and bound to sialic acid in biophysical assays with the same affinity as protein isolated from the virus. A wide range of mutations, including those that have been characterised clinically to result in the development of resistance as well as mutations that we predict might affect inhibitor binding without disrupting activity, have been expressed in insect cells. The biochemical characterisation of these mutants, together with ongoing crystallography efforts, will provide a deeper understanding of the structure-activity relationship that can be used to examine the consequences of these mutations, and any future mutations that might arise, on influenza infectivity and treatment options.