Anti-HA Affinity Gel: A Powerful Tool for Protein Purification Anti-HA affinity gel is a chromatographic resin that contains immobilized anti-HA monoclonal antibodies. This gel is used to purify proteins that have been fused to the HA (hemagglutinin) peptide tag. The HA tag is a short amino acid sequence (YPYDVPDYA) that can be fused to the N- or C-terminus of a protein of interest during recombinant protein expression. How Anti-HA Affinity Gel Works: Protein binding: The HA-tagged protein binds specifically to the anti-HA antibodies immobilized on the gel. Washing: Unbound proteins are washed away. Elution: The bound HA-tagged protein is eluted from the gel using a competitive elution buffer that contains free HA peptide.