Cell lysate was prepared by homogenization of the over-expressed cells in ice-cold modified RIPA Lysis Buffer with cocktail of protease inhibitors (Sigma). Cell debris was removed by centrifugation. Protein concentration was determined by Bradford assay

A DNA sequence encoding the Influenza A virus (A/mallard/Ohio/217/1998(H6N8)) hemagglutinin (ABO52049.1) (Met1-Arg344), termed as HA1, was expressed with a C-terminal polyhistidine tag.