Metal-chelate affinity chromatography

Recombinant proteins engineered to have six consecutive histidine residues on either the amino or carboxyl terminus can be purified using a resin containing nickel ions (Ni(2+)) that have been immobilized by covalently attached nitrilotriacetic acid (NTA). This technique, known as metal-chelate affinity chromatography (MCAC), can readily be performed with either native or denatured protein. This unit discusses techniques for creating a fusion protein consisting of the protein of interest with a histidine tail attached. A procedure for expression of histidine-tail fusion proteins and their purification in native form by MCAC is described, and two alternate protocols describe purification of histidine-tail fusion proteins by MCAC under denaturing conditions and their renaturation by either dialysis or solid-phase renaturation. Support protocols are provided for analysis of the purified product and regeneration of the NTA resin. All of these protocols are easily adaptable to any protein expression system.