ABSTRACT
To express and secrete native HBscFv (anti-HBsAg single-chain Fv) in P. pastoris, HBscFv was amplified from plasmid pGEM-HBscFv, and then sub-cloned into expression vector pPICZalphaA. The resulting plasmid pPIC-HBscFv was linearized and transformed into P. pastoris GS115. The recombinant Pichia strains, identified by direct PCR and Zeocin-resistant screening of Pichia transformants, were cultured and induced with methanol. It was found that recombinant HBscFv, lead by alpha-factor, could be secreted into the culture supernatant to a level of 80mg/L. The bioactivity of Pichia produced HBscFv was confirmed by indirect ELISA, which also suggested that the bioactivity of HBscFv in the culture supernatant reached its peak in 72h and decreased in the late-stage of the induction. PAS staining suggests that HBscFv produced by yeast is poorly glycosylated or none-glycosylated protein.
Subject(s)
Humans , Blotting, Western , Electrophoresis, Polyacrylamide Gel , Hepatitis B Surface Antigens , Allergy and Immunology , Pichia , Genetics , Metabolism , Polymerase Chain Reaction , Single-Chain Antibodies , Genetics , Allergy and Immunology , MetabolismABSTRACT
The cytoplasm of E. coli is a reducing environment where cysteines do not engage in disulfide bonds. Any disulfide bonds that do appear are rapidly reduced through the action of disulfide reducing enzymes such as thioredoxin and glutaredoxin. To study the influence of E. coli cytoplasm on the solubility of recombinant proteins produced in it, bovine fibroblast growth factor (BbFGF), with single disulfide bond, and anti-HBsAg single-chain Fv (HBscFv), with two disulfide bonds, were selected as the pattern molecules of simple protein and complex protein, respectively. pJN98-BbFGF, a BbFGF expressing plasmid based on the vector pET3c, was constructed and transformed into normal host BL21(DE3) and a reductase deficient strain, E. coli Origami(DE3). At the same time, pQE-HBscFv, a HBscFv expressing plasmid was constructed and transformed into M15 [pREP4] and Origami(DE3). The recombinant BbFGF and HBscFv were produced in 2 types of bacteria and their solubilities and bioactivities were determined, respectively. It was found that the majority of BbFGF had formed inclusion body in the cytoplasm of BL21 (DE3) and all of them turned into soluble protein in Origami(DE3). It was also found the productivity of BbFGF in Origami (DE3) was 5% - 10% of the total protein and the value was 15% - 23% in BL21(DE3). BbFGFs produced in 2 recombinant bacteria were purified by cation exchange and heparin affinity chromatography. MTT assay revealed that the bioactivity of BbFGF purified from Origami(DE3) was higher than its counterpart from BL21(DE3). The ED50 of BbFGFs from different bacteria was 1.6ng/mL and 2.2ng/mL, respectively. As far as HBscFvs, both of them formed inclusion body in the cytoplasm of M15 [pQE-HBscFv] and Origami [pQE-HBscFv]. The inclusion body was solubilized in 6mol/L GuHCl, purified with a His-Trap column and then refolded by dialysis step-by-step against buffers containing downtrend concentration of GuHCl. Indirect ELISA was applied to determine the HBsAg binding activity of HBscFvs. It was found there was no obvious difference between the bioactivity of refolded HBscFvs produced from 2 recombinant bacteria. On the other hand, the supernatant of Origami [pQE-HBscFv] lysate displayed weak bioactivity and its counterpart from M15 [pQE-HBscFv] displayed without any bioactivity. The soluble HBsFv in the cytoplasm of Origami [pQE-HBscFv] was purified by cation exchange and immobilized metal affinity chromatography (IMAC) and the yield was 1 - 2mg/L. Those results suggested that modification of the redox environment of E. coli cytoplasm greatly improved the solubility of recombinant disulfide-bonded proteins produced in it. In the next step, we had like to co-express of molecular chaperones or refoldase to raise the yield of soluble recombinant proteins, as well as optimizing the culture condition of the "oxidizing" E. coli.