Regulation and expression of human Fabs under the control of the Escherichia coli arabinose promoter, PBAD

Expression of a Functional zipFv Antibody Fragment and Its Fusions with Alkaline Phosphatase in the Cytoplasm of an Escherichia coli

Background

Expression of recombinant antibodies and their derivatives fused with other functional molecules such as alkaline phosphatase in Escherichia coli is important in the development of molecular diagnostic reagents for biomedical research.

Methods

We investigated the possibility of applying a well-known Fos-Jun zipper to dimerize V_H and V_L fragments originated from the Fab clone (SP 112) that recognizes pyruvate dehydrogenase complex-E2 (PDC-E2), and demonstrated that the functional zipFv-112 and its alkaline phosphatase fusion molecules (zipFv-AP) can be produced in the cytoplasm of Origami(DE3) trxB gor mutant E. coli strain.

Results

The zipFv-AP fusion molecules exhibited higher antigen-binding signals than the zipFv up to a 10-fold under the same experimental conditions. However, conformation of the zipFv-AP seemed to be influenced by the location of an AP domain at the C-terminus of V_H or V_L domain [zipFv-112(H-AP) or zipFv-112(L-AP)], and inclusion of an AraC DNA binding domain at the C-terminus of V_H of the zipFv-112(L-AP), termed zipFv-112(H-AD/L-AP), was also beneficial. Cytoplasmic co-expression of disulfide-binding isomerase C (DsbC) helped proper folding of the zipFv-112(H-AD/L-AP) but not significantly.

Conclusion

We believe that our zipFv constructs may serve as an excellent antibody format bi-functional antibody fragments that can be produced stably in the cytoplasm of E. coli.

Controlled expression of cholera toxin B subunit from Vibrio cholerae in Escherichia coli

The ctxB gene, the causative agent of cholera epidemic was successfully cloned from V. cholerae in E. coli. The insertion of the gene was confirmed by PCR as well as restriction digestion analyses. The sequencing results for the gene confirmed that the insert was in the correct orientation and in-frame with the P(BAD) promoter and it showed that the gene was 99% homologous to the published ctxB sequence. The CTB protein was successfully expressed in E. coli using the pBAD/His vector system. The expected protein of approximately 14 kDa was detected by SDS-PAGE and Western blot. The use of pBAD/His vector to express the cholera toxin gene in E. coli would facilitate future study of toxin gene products.

Antibody engineering

Antibodies are unique in their high affinity and specificity for a binding partner, a quality that has made them one of the most useful molecules for biotechnology and biomedical applications. The field of antibody engineering has changed rapidly in the past 10 years, fueled by novel technologies for the in vitro isolation of antibodies from combinatorial libraries and their functional expression in bacteria. This review presents an overview of the methods available for the de novo generation of human antibodies, for engineering antibodies with increased antigen affinity, and for the production of antibody fragments. Select applications of recombinant antibodies are also presented.

Selectable in-vivo recombination to increase antibody library size--an improved phage display vector system

Phage display technology permits the display of libraries of random combinations of light (LC) and heavy chain (HC) antibody genes. Maximizing the size of these libraries would enable the isolation of antibodies with high affinity and specificity. In this study, the loxP/Cre system of in-vivo recombination has been employed to construct an improved vector system for the display of antibodies. In this system, the chloramphenicol acetyl transferase (CAT) gene is linked to a HC library in a donor plasmid, pUX. This CAT gene is 'silent' before recombination but active after recombination. A second acceptor phagemid, pMOX, is used for cloning the LC repertoire. Following infection with a Cre producing phage, pMOX accepts the CAT/HC library from pUX via site-specific recombination at the loxP sites. Recombinants can then be selected via chloramphenicol resistance. Using this vector system, we have generated libraries of 4x109 recombinants. Restriction analysis and Fab expression confirmed that 100% of the colonies in the library were recombinants. This system provides a stable selectable mechanism for the generation of large libraries and avoids the isolation of non-recombinants encountered with earlier in-vivo recombination systems.