Nickel-ion substituted hydroxyapatite matrices for metal-affinity chromatographic purification of recombinant proteins

Hydroxyapatite (HAp) is a calcium phosphate ceramic, widely used as a matrix for protein chromatography. The crystal structure of HAp is amenable to a wide range of substitutions, thus allowing for the alteration of its properties. In this study, nickel-ion substituted HAp (NiSHAp) was synthesized using a wet-precipitation method, followed by spray drying. This resulted in the structural incorporation of nickel ions within well-defined microspheres, which were suitable for chromatographic applications. The chromatographic experiments were conducted with NiSHAp and compared with spray-dried hydroxyapatite (SHAp) matrices. Protein purification experiments were conducted using refolded recombinant L-asparaginase (L-Asp), which was produced as inclusion bodies in Escherichia coli. The results showed that NiSHAp effectively adsorbed L-Asp, which was selectively eluted using a phosphate buffer, surpassing the efficiency of imidazole-based elution. In contrast, SHAp showed weaker binding and lower selectivity. The significance of this study lies in developing a scalable NiSHAp matrix for protein purification, especially for large-scale applications. The NiSHAp matrix offers a cost-effective alternative to commercial immobilized metal affinity chromatography (IMAC) adsorbents, especially for purifying His-tagged proteins. This innovative approach exhibits the advantages of mixed-mode chromatography by combining the properties of hydroxyapatite and IMAC in a single matrix, with the potential of improved industrial-scale protein purification.