Description

His-tag protein purification by IMAC is both popular and highly efficient. HisTrap HP columns are packed with Ni Sepharose High Performance (HP) affinity resin. This resin consists of highly cross-linked agarose beads to which a chelating group has been coupled. The chelating group is precharged with nickel, which selectively retains proteins with exposed histidine groups. HisTrap HP columns can also be used for the purification of tagged proteins containing shorter or longer polyhistidine tags, such as (histidine)4 or (histidine)1. The shorter (histidine)4 will bind more weakly and the longer (histidine)1 will bind more strongly compared with (histidine)6. This difference in binding strength can be used during purification; since (histidine)1 binds more strongly, a higher concentration of imidazole can be added to the lysed cells. This can facilitate the removal of contaminants that can otherwise be copurified with the tagged target protein.