His-tag provides a way to specifically detect orpurify proteins of interest without the need to use protein-specific antibodyor probes (Waugh, 2011). IndeedHis- tag has been widely used to enhance protein purification by severaltechniques one of which is called immobilized metal affinity chromatography (Randolph, 2011). The underlying basis of IMAC method is theinteraction between atransition metal ion such as copper (Cu2+), cobalt (Co2+), nickel(Ni2+), zinc (Zn2+), calcium (Ca2+), and Iron III (Fe3+) immobilized on a matrix and specific amino acid sidechains (Randolph, 2011). Histidine is one of the amino acids that canstrongly interact and form coordinate bonds with the immobilized transitionmetal ions (Bang and Kent,2005).

This allows purification of  His-tagged protein from complex mixtures thatis only His-tagged protein is effectively retained on IMAC column matrices (Bang and Kent,2005). Thetype of metal ion used in IMAC is based on the objective of the application.For example, if the primary concern was His-tagged protein purification thencobalt is the ideal ion metal to use since it exhibits more specificinteraction with His-tag than all of the other metal ions (Bang and Kent,2005). His-tagged protein can be easily eluted from the column by eitheradjusting the buffer pH or adding free imidazole to the column buffer