One-step orientated immobilization of nanobodies and its application for immunoglobulin purification

Affinity chromatography technologies play an important role in the purification of antibodies. To prepare affinity materials, prior isolation and purification of affinity ligands are required before coupling onto solid supports, which is quite expensive and laborious in large-scale applications. In this study, a one-step approach which circumvents the ligand purification procedures was developed to fabricate affinity gel for purifying immunoglobulin G (IgG). A self-labeling tag, haloalkane dehalogenase, was fused to the C-terminal of an anti-Fc variable domain of the heavy chain of the heavy-chain antibody (AFV) which was isolated in previous work. The AFV binds to various sources of IgG and is highly thermal stable. The fusion protein, namely HAFV, was expressed in Escherichia coli as a soluble protein. The binding affinity of HAFV to the Fc region of IgG was characterized and compared with the untagged anti-Fc nanobody. Next, the HAFV was immobilized directly from the crude cell lysate of isopropylthio-β-D-galactoside (IPTG) induced E. coli. The effects of NaCl concentrations and pH on the capacity of the HAFV resin were investigated. In addition, the one-step coupled HAFV resin was compared with the AFV resin and commercial resins (Protein A and Protein G) by evaluating the static capacity and stability. Though the Protein A (8.34 ± 0.37 mg/ml) and Protein G (9.19 ± 0.28 mg/ml) showed higher static capacity, the static capacity of HAFV resin (8.21 ± 0.30 mg/ml) was better than that of the untagged AFV gel (6.48 ± 0.56 mg/ml). The recovery results calculated for the reusability and stability show that there is no significant difference between the results obtained for the HAFV gel with those of the untagged AFV gel and commercial Protein A and G. After stored at 37 ℃ for 7 days and recycled 10 times, the static capacity of HAFV gel remains above 78%. Our strategy is site-specific, cost-effective, reproducible, and has the potential to dramatically cut down the costs of affinity materials for IgG purification.