Expression, Purification, and Characterization of Anti-Plumbagin Single-Chain Variable Fragment Antibody in Sf9 Insect Cell

Plumbagin (PL; 5-hydroxy-2-methyl-1, 4-naphthoquinone) is an important secondary metabolite, mainly produced in the Plumbago zeylanica L. (Plumbaginaceae). A single-chain variable fragment (scFv) antibody, fusion of the variable regions of the heavy chain and light chain of immunogloblin against PL (PL-scFv) was expressed by Bac-to-Bac Baculovirus Expression System using Spodoptera frugiperda (Sf9) insect cells and characterized to investigate potential use of PL-scFv as a tool for plant immunomodulation. Functional PL-scFv expressed in the Sf9 insect cells were purified using cation exchange chromatography followed by immobilized metal ion affinity chromatography (IMAC). The yields of the purified PL-scFv in the culture supernatant and Sf9 insect cells were 2.0 mg and 5.2 mg per 1 liter of Sf9 culture medium, respectively. Recombinant purified PL-scFv was then characterized by the indirect competitive enzyme-linked immunosorbent assay (ELISA). The cross-reactivity and sensitivity of PL-scFv expressed in Sf9 insect cells were compared with PL-scFv expressed in Escherichia coli and its parental anti-plumbagin monoclonal antibody (MAb 3A3) secreted from hybridoma cells. Intriguingly, the specificity of the PL-scFv expressed in Sf9 insect cells was found to be different from that expressed in E. coli and parental MAb 3A3, although the detectable level (0.2-25 mu g/mL) was the same in ELISA using each antibody. Even more interestingly, the characteristics of PL-scFv, which have wide cross-reactivity against 1,4-napththoquinone, suggest its potential use as a tool for plant immunomodulation not only for breeding Plumbaginacea family containing PL but also for breeding other medicinal plants containing bioactive naphthoquinones.