Metal chelate affinity chromatography
Metal chelate affinity chromatography is a pseudoaffinity protein purification technique first developed in the 1970s. The mode of adsorption relies upon the formation of weak coordinate bonds between basic groups on a protein surface with metal ions immobilized on chromatographic beads (Figure 6.17). The affinity medium is synthesized by covalent attachment of a metal chelator to the chromatographic bead via a spacer arm. Chelating agents, such as iminodiacetate, are capable of binding a number of metal ions (e.g. Fe, Co, Ni, Cu, Zn, Al), and binding effectively immobilizes the ion on the bead. The affinity gel is normally supplied without bound metal, so the gel can be 'charged' with the metal of choice (by flushing the column with a solution containing a salt of that metal, e.g. CuSO4 in the case of copper). The metal ions most commonly used are Zn2+, Ni2+ and Cu2+. Basic groups on protein surfaces, most notably the side chain of histidine residues,
Matrix bead
Spacer arm
Metal chelator
Metal chelator
Spacer arm
Immobilized metal
Immobilized metal
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