Rapid two-step purification of a recombinant mouse Fab fragment expressed in Escherichia coli

Cytoplasmic production of Fabs in chemically defined media in fed-batch fermentation

Fragment of antigen-binding region (Fab) of antibodies are important biomolecules, with a broad spectrum of functionality in the biomedical field. While full length antibodies are usually produced in mammalian cells, the smaller size, lack of N-glycosylation and less complex structure of Fabs make production in microbial cell factories feasible. Since Fabs contain disulfide bonds, such production is often done in the periplasm, but there the formation of the inter-molecular disulfide bond between light and heavy chains can be problematic. Here we studied the use of the CyDisCo system (cytoplasmic disulfide bond formation in E. coli) to express two Fabs (Herceptin and Maa48) in the cytoplasm of E. coli in fed-batch fermentation using a generic chemically defined media. We were able to solubly express both Fabs with purified yields of 565 mg/L (Maa48) and 660 mg/L (Herceptin) from low density fermentation. Both proteins exhibited CD spectra consistent with natively folded protein and both were biologically active. To our knowledge this is the first demonstration of high-level production of biological active Fabs in the cytoplasm of E. coli in industrially relevant fermentation conditions.

Bacterial production and structure-functional validation of a recombinant antigen-binding fragment (Fab) of an anti-cancer therapeutic antibody targeting epidermal growth factor receptor

Fragment engineering of monoclonal antibodies (mAbs) has emerged as an excellent paradigm to develop highly efficient therapeutic and/or diagnostic agents. Engineered mAb fragments can be economically produced in bacterial systems using recombinant DNA technologies. In this work, we established recombinant production in Escherichia coli for monovalent antigen-binding fragment (Fab) adopted from a clinically used anticancer mAB drug cetuximab targeting epidermal growth factor receptor (EGFR). Recombinant DNA constructs were designed to express both polypeptide chains comprising Fab in a single vector and to secrete them to bacterial periplasmic space for efficient folding. Particularly, a C-terminal engineering to confer an interchain disulfide bond appeared to be able to enhance its heterodimeric integrity and EGFR-binding activity. Conformational relevance of the purified final product was validated by mass spectrometry and crystal structure at 1.9 Å resolution. Finally, our recombinant cetuximab-Fab was found to have strong binding affinity to EGFR overexpressed in human squamous carcinoma model (A431) cells. Its binding ability was comparable to that of cetuximab. Its EGFR-binding affinity was estimated at approximately 0.7 nM of Kd in vitro, which was quite stronger than the binding affinity of natural ligand EGF. Hence, the results validate that our construction could serve as an efficient platform to produce a recombinant cetuximab-Fab with a retained antigen-binding functionality.

Production of a new non-specific nuclease from Yersinia enterocolitica subsp. palearctica: optimization of induction conditions using response surface methodology

A new non-specific nuclease from Yersinia enterocolitica subsp. palearctica (Y. NSN) was expressed in Escherichia coli (E. coli) BL 21 Star^TM (DE3)plysS. Induction conditions, including isopropyl-β-D-thiogalactoside (IPTG) concentration, cell density (OD600), induction time and induction temperature, were optimized using response surface methodology. Statistical analysis of the results revealed that induction temperature and all the quadratic terms of variables had significant effects on enzyme activity of Y. NSN. The optimal induction conditions were as follows: 1.5 mmol/L IPTG, OD600 of 0.80, induction time of 20.5 h, and induction temperature of 32 °C. Under the optimized conditions, the highest enzyme activity could be obtained.

Generation of recombinant antibodies and means for increasing their affinity

Highly specific interaction with foreign molecules is a unique feature of antibodies. Since 1975, when Keller and Milstein proposed the method of hybridoma technology and prepared mouse monoclonal antibodies, many antibodies specific to various antigens have been obtained. Recent development of methods for preparation of recombinant DNA libraries and in silico bioinformatics approaches for protein structure analysis makes possible antibody preparation using gene engineering approaches. The development of gene engineering methods allowed creating recombinant antibodies and improving characteristics of existing antibodies; this significantly extends the applicability of antibodies. By modifying biochemical and immunochemical properties of antibodies by changing their amino acid sequences it is possible to create antibodies with properties optimal for certain tasks. For example, application of recombinant technologies resulted in antibody preparation of high affinity significantly exceeding the initial affinity of natural antibodies. In this review we summarize information about the structure, modes of preparation, and application of recombinant antibodies and their fragments and also consider the main approaches used to increase antibody affinity.

Optimization of phenazine-1-carboxylic acid production by a gacA/qscR-inactivated Pseudomonas sp. M18GQ harboring pME6032Phz using response surface methodology

Phenazine-1-carboxylic acid (PCA) production was enhanced in Pseudomonas sp. M18 wild strain and its mutants carrying recombinant pME6032Phz for phz gene cluster overexpression, among which Pseudomonas sp. strain M18GQ/pME6032Phz, a gacA and qscR double gene chromosomally inactivated mutant harboring pME6032Phz, showed the highest PCA yield. The conditions for fermentation and isopropyl-beta-D-1-thiogalactopyranoside (IPTG) induction were optimized for strain M18GQ/pME6032Phz in shake flask experiments. A one-factor-at-a-time approach, followed by a fractional factorial design identified soybean meal, corn steep liquor, and ethanol as statistically significant factors. Optimal concentrations and mutual interactions of the factors were then determined by the method of steepest ascent and by response surface methodology based on the center composite design. The predicted PCA production was 6,335.2 mg/l after 60 h fermentation in the optimal medium of 65.02 g soybean meal, 15.36 g corn steep liquor, 12 g glucose, 21.70 ml ethanol, and 1 g MgSO(4) per liter in the flask fermentations, with induction of 1.0 mmol/l IPTG 24 h after inoculation. In an experimental validation under these conditions, the maximum PCA production was 6,365.0 mg/l. This represents a approximately 60% increase over production by strain M18GQ in optimal conditions. The negative effect of plasmid pME6032 on the expression of chromosomally located phz gene cluster was found in Pseudomonas sp. M18GQ, and the possible reason was discussed in the text.

Ion exchange chromatography of antibody fragments

Effects of pH and conductivity on the ion exchange chromatographic purification of an antigen-binding antibody fragment (Fab) of pI 8.0 were investigated. Normal sulfopropyl (SP) group modified agarose particles (SP Sepharosetrade mark Fast Flow) and dextran modified particles (SP Sepharose XL) were studied. Chromatographic measurements including adsorption isotherms and dynamic breakthrough binding capacities, were complemented with laser scanning confocal microscopy. As expected static equilibrium and dynamic binding capacities were generally reduced by increasing mobile phase conductivity (1-25 mS/cm). However at pH 4 on SP Sepharose XL, Fab dynamic binding capacity increased from 130 to 160 (mg/mL media) as mobile phase conductivity changed from 1 to 5 mS/cm. Decreasing protein net charge by increasing pH from 4 to 5 at 1.3 mS/cm caused dynamic binding capacity to increase from 130 to 180 mg/mL. Confocal scanning laser microscopy studies indicate such increases were due to faster intra-particle mass transport and hence greater utilization of the media's available binding capacity. Such results are in agreement with recent studies related to ion exchange of whole antibody molecules under similar conditions.

Optimization of a nonradioactive method for consistent and sensitive determination of activated K-ras protein

Accurate measurement of activity of wild-type K-ras protein is important due to its tumor suppressor action in tissues such as lung. A published method by Taylor and co-workers uses plasmid-containing Escherichia coli cells to produce a glutathione-S-transferase/raf-1 ras binding domain (GST-RBD) fusion protein attached to glutathione beads to isolate activated ras protein. We systematically optimized the method before use on lung tissues. Changing the GST-RBD protein induction temperature from the original 37 to 30 degrees C produced a consistently greater yield of fusion protein. To improve stability of the GST-RBD beads so as to perform large-scale experiments, 0.1% NaN(3) was added. NaN(3)-treated beads retained full affinity for at least 24 days. Sensitivity was improved by using a polyvinylidene difluoride membrane rather than nitrocellulose for immunoblotting. We also compared our GST-RBD beads with two commercial assay kits and found that our beads had both superior sensitivity and reduced variability. In summary, our modification of the GST-RBD affinity method to recover activated K-ras greatly increased the yield of fusion protein, prolonged the useful life of GST-RBD beads to at least 24 days, and enhanced detection sensitivity.

Isolation of antigens and antibodies by affinity chromatography

Antibody-antigen binding constants are commonly strong enough for an effective affinity purification of antibodies (by immobilized antigens) or antigens (by immobilized antibodies) to work out a straightforward purification method. A drawback is that antibodies are large protein molecules and subject to denaturation under conditions required for the elution from the complex. Structures of antigens can vary but usually antigens are also equally subject to similar problems. The lability of the components can sometimes make the procedure sophisticated, but usually in all cases it is possible to find a satisfactory approach. In certain cases, specific interactions of the Fc part of antibodies are more facile to exploit for their purification.