Immobilised Metal Affinity Chromatography (IMAC)

As early as 1975, the first paper on immobilized metal ion chromatography (IMAC) was published by J. Porath (1). He showed that a chelating group bound to an agarose matrix had very high selectivity for certain proteins when different metal ions were used. The interaction involves the formation of a metal complex between the immobilized transition metal ion and electron donor amino acids in the protein. Through the use of model proteins, it was shown that histidine, tryptophan and cysteine were involved as donors. By altering the chelating group and using different metal ions it is possible to obtain extremely high selectivity for certain proteins. Iminodiacetic acid (IDA) is the standard chelator used on commercially available media and the most frequently used metal ions are Zn2+, Ni2+, Co2+, Ca2+, Cu2+and Fe3+. The bound proteins can be released either by lowering the pH or by introducing competitive ions such as imidazole or chelating agents such as EDTA.

The importance of ligand density in IMAC has been shown to be of significant importance for maximum resolution of proteins and peptides. Thus, it is highly beneficial to have available both a low and a high ligand density media.

IMAC is an excellent method for the purification of histidine tagged proteins, membrane proteins or any protein with available histidine, tryptophan or cysteine groups.


Reference
1. J. Porath et al., Nature 258, 598-599 (1975).