Chromatography adsorbent and purification of histidine tagged proteins

This article discusses a recently created process for the production of a new affinity ligand, Fe3O4/SiO2-GPTMS-Asp-C, which is based on a recently published paper.
When the Fe3O4/SiO2-GPTMS-Asp-C ligand is bound to histidine-tagged proteins, the proteins are able to be separated from cell lysate, which is the mixture of cell parts within the cell wall.
The main result from using the Fe3O4/SiO2-GPTMS-Asp-C nanoparticle in the separation is that it produces a purity even higher than that of conventional ligands.
Due to the nature of the separation, there are certain properties it is desireable for the ligand to have.
Firstly, the ideal affinity tag should enable effective but not too strong a binding, and allow elution of the desired protein under mild, nondestructive conditions<ref name = "feng"/>. In the common ligands the binding force of with the metal ion is weak<ref name = "feng"/>. This is because the metal atom is bound once to the protein-nanoparticle complex. However, the goal of this synthesis is the creation of a ligand which allows for two bonds between the metal and the protein-nanoparticle complex<ref name = "feng"/>. The result of this new ligand with two bonds is a greater retention power with the protein compared to other ligands<ref name = "feng"/>.
Synthesis steps
Due to the complexity of the steps involved in the creation of these nanoparticles, a brief overview of the steps will be provided, with a link being provided for a more detailed description of the synthesis.
* Firstly, the Fe3O4 were prepared, and the resulting particles were then modified by SiO2.
* Secondly, epoxy groups were added through the condensation between 3-glycidoxypropyltrimethoxysilane (GPTMS) and OH of SiO2.
* Thirdly, two carboxylic groups were introduced by the reaction between amine group of l-aspartic acid (l-Asp) and epoxy groups of GPTMS. Another carboxylic group was introduced by reaction between bromine of 2-bromoacetic acid and imino group in the product prepared above step. The resulting product denominated Fe3O4/SiO2-GPTMS-Asp was obtained.
* Finally, Co2+ was attached on Fe3O4/SiO2-GPTMS-Asp through coordination of three carboxylic groups and N atom of tertiary amine with Co2+. The result of these steps was that the final nanoparticles named Fe3O4/SiO2-GPTMS-Asp-Co were obtained<ref name = "feng" />.
Results
The results from the separation performed using the Fe3O4/SiO2-GPTMS-Asp-Co nanoparticle indicate that the particle achieved its goal remarkably well<ref name = "feng"/>. Analysis confirmed that the Fe3O4/SiO2-GPTMS-Asp-Co particle was within the desired size range, with the distribution of diameters spanning from 214-219 nm<ref name = "feng"/>.
The results also indicated that when this particle is used in the separation, the occurrence of other proteins in the separated mixture are undetectable while significant amounts of the desired protein were separated<ref name = "feng"/>. Also indicated was that the IMAC adsorbent that was prepared has the advantages of simple operation, good selectivity, moderate binding force of the histidine-tagged proteins and higher capacity<ref name = "feng" />.

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