Affinity Based Nano-Magnetic Particles for Purification of Recombinant Proteins in Form of Inclusion Body

Protein purification is the most complicated issue in the downstream processes of recombinant protein production; therefore, improved selective purification methods are important. Affinity-based protein purification method using polyhistidine-tag (His-tag) and nickel-nitrilotriacetic acid (Ni-NTA) resins is one of the most common strategies. Magnetic nanoparticles (MNPs) can be used as a beneficial alternative for Ni-NTA resins. However, there is no data on the capability of MNPs for protein purification from inclusion bodies; this issue is studied here.

Recombinant His-tagged proteins of enhanced green fluorescent protein (EGFP)-His and streptokinase (SK)-His were expressed in E. coli BL-21 (DE3) in soluble and inclusion body forms, respectively. MNPs including Fe3O4 magnetic core, SiO2 shell, and Ni2+ on the surface were synthesized by sol-gel and hydrothermal reactions and then characterized by X-ray powder diffraction, vibrating sample magnetometer, and scanning electron microscopy imaging. Both synthesized Fe3O4@NiSiO3 and Fe3O4@NixSiOy MNPs were employed to purify EGEP-His and SK-His under native and denaturing conditions, respectively. The quantity and purity of purified proteins were analyzed by micro-Bradford assay and SDS-PAGE, respectively.

Both synthesized MNPs were spherical and well-dispersed with the size ranging from 290 to 415 nm. Synthesized MNPs contained Fe3O4, SiO2 shell, and Ni2+ on their structures with suitable magnetization properties. Using Fe3O4@NiSiO3 and Fe3O4@NixSiOy yielded 192 and 188 µg/mg of SK-His, as compared to 207 and 195 µg/mg of EGFP-His, respectively.

MNPs containing magnetic Fe3O4 core, SiO2 shell, and Ni2+on their surface are versatile alternatives for Ni-NTA resins in protein purification for proteins expressed in both soluble and inclusion body forms.