Polyhistidine tag (6×His tag) (6×His)

The 6×His tag is a synthetic peptide consisting of six consecutive histidine residues, commonly engineered into the N- or C-terminus of recombinant proteins to facilitate their purification and detection. It functions by binding with high affinity to immobilized divalent metal ions, such as nickel (Ni2+) or cobalt (Co2+), through coordinate covalent bonding in a process known as Immobilized Metal Affinity Chromatography (IMAC) (Hochuli et al., 1988). This tag is one of the most prevalent tools in biotechnology due to its small size, which typically minimizes impact on protein solubility, and its ability to remain stable under both native and denaturing conditions (Terpe, 2003). In a therapeutic context, the 6×His tag is not a target for drug intervention but rather a manufacturing aid; it is often removed from the final drug product using site-specific proteases to ensure the protein maintains its native conformation and to minimize potential adverse immune responses in patients (Khan et al., 2012). Consequently, while it is indispensable for protein characterization and production, it does not possess an endogenous biological role or direct involvement in disease pathogenesis.

Other names

His6 tagHexahistidine tagHis-tag6-His tagPoly-His tagHHHHHH epitope

The 6×His tag facilitates the purification of recombinant proteins through Immobilized Metal Affinity Chromatography (IMAC). The imidazole rings of the histidine residues form coordinate covalent bonds with transition metal ions (such as Ni2+ or Co2+) immobilized on a resin (Porath et al., 1975; Hochuli et al., 1988). Elution is typically achieved using imidazole, which competes for the metal binding sites, or by lowering the pH to protonate the histidine residues (Bornhorst & Falke, 2000).