Final answer:
To target histidine-containing proteins in IMAC, you attach a metal ion such as nickel, copper, zinc, or cobalt to the resin, which binds the histidine residues, allowing purification of these proteins.
Step-by-step explanation:
In Immobilized Metal Affinity Chromatography (IMAC), if you were targeting histidine-containing proteins, you would attach a metal ion to the resin that specifically binds to histidine residues. The most commonly used metals for this purpose are nickel (Ni2+), copper (Cu2+), zinc (Zn2+), and cobalt (Co2+). These metal ions have a high affinity for the imidazole ring of histidine and can be used to purify proteins that have accessible histidine residues on their surface. In practical application, proteins are passed over the resin where histidine residues form coordination bonds with the immobilized metal ions. Unbound proteins are washed away, and the target histidine-containing proteins can then be eluted using a solution containing a competitive agent, such as imidazole or histidine, which disrupts the interaction between the metal ions and the protein's histidine residues.