How additives influence the refolding of immunoglobulin-folded proteins in a stepwise dialysis system. Spectroscopic evidence for highly efficient refolding of a single-chain Fv fragment

Refolding techniques for recovering biologically active recombinant proteins from inclusion bodies

Biologically active proteins are useful for studying the biological functions of genes and for the development of therapeutic drugs and biomaterials in a biotechnology industry. Overexpression of recombinant proteins in bacteria, such as Escherichia coli, often results in the formation of inclusion bodies, which are protein aggregates with non-native conformations. As inclusion bodies contain relatively pure and intact proteins, protein refolding is an important process to obtain active recombinant proteins from inclusion bodies. However, conventional refolding methods, such as dialysis and dilution, are time consuming and, often, recovered yields of active proteins are low, and a trial-and-error process is required to achieve success. Recently, several approaches have been reported to refold these aggregated proteins into an active form. The strategies largely aim at reducing protein aggregation during the refolding procedure. This review focuses on protein refolding techniques using chemical additives and laminar flow in microfluidic chips for the efficient recovery of active proteins from inclusion bodies.

Affinity improvement of a therapeutic antibody by structure-based computational design: generation of electrostatic interactions in the transition state stabilizes the antibody-antigen complex

The optimization of antibodies is a desirable goal towards the development of better therapeutic strategies. The antibody 11K2 was previously developed as a therapeutic tool for inflammatory diseases, and displays very high affinity (4.6 pM) for its antigen the chemokine MCP-1 (monocyte chemo-attractant protein-1). We have employed a virtual library of mutations of 11K2 to identify antibody variants of potentially higher affinity, and to establish benchmarks in the engineering of a mature therapeutic antibody. The most promising candidates identified in the virtual screening were examined by surface plasmon resonance to validate the computational predictions, and to characterize their binding affinity and key thermodynamic properties in detail. Only mutations in the light-chain of the antibody are effective at enhancing its affinity for the antigen in vitro, suggesting that the interaction surface of the heavy-chain (dominated by the hot-spot residue Phe101) is not amenable to optimization. The single-mutation with the highest affinity is L-N31R (4.6-fold higher affinity than wild-type antibody). Importantly, all the single-mutations showing increase affinity incorporate a charged residue (Arg, Asp, or Glu). The characterization of the relevant thermodynamic parameters clarifies the energetic mechanism. Essentially, the formation of new electrostatic interactions early in the binding reaction coordinate (transition state or earlier) benefits the durability of the antibody-antigen complex. The combination of in silico calculations and thermodynamic analysis is an effective strategy to improve the affinity of a matured therapeutic antibody.

Arginine inhibits adsorption of proteins on polystyrene surface

Nonspecific adsorption of protein on solid surfaces causes a reduction of concentration as well as enzyme inactivation during purification and storage. However, there are no versatile inhibitors of the adsorption between proteins and solid surfaces at low concentrations. Therefore, we examined additives for the prevention of protein adsorption on polystyrene particles (PS particles) as a commonly-used material for vessels such as disposable test tubes and microtubes. A protein solution was mixed with PS particles, and then adsorption of protein was monitored by the concentration and activity of protein in the supernatant after centrifugation. Five different proteins bound to PS particles through electrostatic, hydrophobic, and aromatic interactions, causing a decrease in protein concentration and loss of enzyme activity in the supernatant. Among the additives, including arginine hydrochloride (Arg), lysine hydrochloride, guanidine hydrochloride, NaCl, glycine, and glucose, Arg was most effective in preventing the binding of proteins to PS particles as well as activity loss. Moreover, even after the mixing of protein and PS particles, the addition of Arg caused desorption of the bound protein from PS particles. This study demonstrated a new function of Arg, which expands the potential for application of Arg to proteins.

Protein-associated cation clusters in aqueous arginine solutions and their effects on protein stability and size

Arginine is one of the most prominent residues in protein interactions, and arginine hydrochloride is widely used as an additive in protein solutions because of its exceptional effects on protein association and folding. The molecular origins of arginine effects on protein processes remain, however, controversial, and little is known about the molecular interactions between arginine cations and protein surfaces in aqueous arginine solutions. In this study, we report a unique biochemical phenomenon whereby clusters of arginine cations (Arg(+)) are associated with a protein surface. The formation of protein-associated Arg(+) clusters is initiated by Arg(+) ions that associate with specific protein surface loci through cooperative interactions with protein guanidinium and carboxyl groups. Molecular dynamics simulations indicate that protein-associated Arg(+) ions subsequently attract other Arg(+) ions and form dynamic cation clusters that extend further than 10 Å from the protein surface. The effects of arginine on the thermal stability and size of lysozyme and ovalbumin are measured over a wide concentration range (0 to 2 M), and we find that the formation of protein-associated Arg(+) clusters consistently explains the complex effects of arginine on protein stability and size. This study elucidates the molecular mechanisms and implications of cluster formation of Arg(+) ions at a protein surface, and the findings of this study may be used to manipulate synthetic and biological systems through arginine-derived groups.

Efficient refolding of a recombinant abzyme : structural and catalytic characterizations

Catalytic antibodies are currently being investigated in order to understand their role under physio-pathological situations. To this end, the knowledge of structure-function relationships is of great interest. Recombinant scFv fragments are smaller and easier to genetically manipulate than whole antibodies, making them well suited for this kind of study. Nevertheless they are often described as proteins being laborious to produce. This paper describes a highly efficient method to produce large quantities of refolded soluble catalytic scFv. For the first time, the functionality of a refolded catalytic scFv displaying a β-lactamase activity has been validated by three approaches: (1) use of circular dichroism to ensure that the refolded had secondary structure consistent with a native scFv fold, (2) development of enzyme-linked immunosorbant assay and surface plasmon resonance (SPR) approaches for testing that the binding characteristics of an inhibitory peptide have been retained, and (3) proof of the subtle catalytic properties conservation through the development of a new sensitive catalytic assay using a fluorogenic substrate.

A simplified method for the efficient refolding and purification of recombinant human GM-CSF

Human granulocyte macrophage colony-stimulating factor (hGM-CSF) is a haematopoietic growth factor and proinflammatory cytokine. Recombinant hGM-CSF is important not only as a research tool but also as a biotherapeutic. However, rhGM-CSF expressed in E. coli is known to form inclusion bodies of misfolded, aggregated protein. Refolding and subsequent purification of rhGM-CSF from inclusion bodies is difficult with low yields of bioactive protein being produced. Here we describe a method for the isolation, refolding and purification of bioactive rhGM-CSF from inclusion bodies. The method is straightforward, not requiring extensive experience in protein refolding nor purification and using standard laboratory equipment.

Direct intracellular selection and biochemical characterization of a recombinant anti-proNGF single chain antibody fragment

proNGF, the precursor of the neurotrophin NGF, is widely expressed in central and peripheral nervous system. Its physiological functions are still largely unknown, although it emerged from studies in the last decade that proNGF has additional and distinct functions with respect to NGF, besides acting chaperone-like for NGF folding during its biogenesis. The regulation of proNGF/NGF ratio represents a crucial process for homeostasis of brain and other tissues, and understanding the molecular aspects of these differences is important. We report the selection and characterization of a recombinant monoclonal anti-proNGF antibody in single chain Fv fragment (scFv) format. The selection exploited the Intracellular Antibody Capture Technology (IACT), starting from a naïve mouse SPLINT (Single Pot Library of INTracellular antibodies) library. This antibody (scFv FPro10) was expressed recombinantly in Escherichia coli, was proven to be highly soluble and stable, and thoroughly characterized from the biochemical-biophysical point of view. scFv FPro10 displays high affinity and specificity for proNGF, showing no cross-reactivity with other pro-neurotrophins. A structural model was obtained by SAXS. scFv FPro10 represents a new tool to be exploited for the selective immunoanalysis of proNGF, both in vitro and in vivo, and might help in understanding the molecular function of proNGF in neurodegeneration.

Preparation of a single-chain variable fragment and a recombinant antigen-binding fragment against the anti-malarial drugs, artemisinin and artesunate, and their application in an ELISA

Two different recombinant antibodies, a single-chain variable fragment (scFv) and an antigen-binding fragment (Fab), were prepared against artemisinin (AM) and artesunate (AS) and were developed for use in an enzyme-linked immunosorbent assay (ELISA). The recombinant antibodies, which were derived from a single monoclonal antibody against AM and AS (mAb 1C1) prepared by us, were expressed by Escherichia coli cells and their reactivity and specificity were characterized. As a result, to obtain sufficient signal in indirect ELISA, a much greater amount of a first antibody was needed in the use of scFv due to the differences of the secondary antibody and conformational stability. Therefore, we focused on the development of the recombinant Fab antibodies and applied it to indirect competitive ELISA. The specificity of the Fab was similar to that of mAb 1C1 in that it showed specific reactivity toward AM and AS only. The sensitivity of the icELISA (0.16 μg/mL to 40 μg/mL for AM and 8.0 ng/mL to 60 ng/mL for AS) was sufficient for analysis of antimalarial drugs, and its utility for quality control of analysis of Artemisia spp. was validated. The Fab expression and refolding systems provided a good yield of high-quality antibodies. The recombinant antibody against AM and AS provides an essential component of an economically attractive immunoassay and will be useful in other immunochemical applications for the analysis and purification of antimalarial drugs.

Using folding promoting agents in recombinant protein production: a review

Recombinant production has become an invaluable tool for supplying research and therapy with proteins of interest. The target proteins are not in every case soluble and/or correctly folded. That is why different production parameters such as host, cultivation conditions and co-expression of chaperones and foldases are applied in order to yield functional recombinant protein. There has been a constant increase and success in the use of folding promoting agents in recombinant protein production. Recent cases are reviewed and discussed in this chapter. Any impact of such strategies cannot be predicted and has to be analyzed and optimized for the corresponding target protein. The in vivo effects of the agents are at least partially comparable to their in vitro mode of action and have been studied by means of modern systems approaches and even in combination with folding/activity screening assays. Resulting data can be used directly for experimental planning or can be fed into knowledge-based modelling. An overview of such technologies is included in the chapter in order to facilitate a decision about the potential in vivo use of folding promoting agents.

Preparation and immunogenicity of tag-free recombinant human eppin

Human epididymal protease inhibitor (eppin) may be effective as a male contraceptive vaccine. In a number of studies, eppin with an engineered His(6)-tag has been produced using prokaryotic expression systems. For production of pharmaceutical-grade proteins for human use, however, the His(6)-tag must be removed. This study describes a method for producing recombinant human eppin without a His(6)-tag. We constructed plasmid pET28a (+)-His(6)-tobacco etch virus (TEV)-eppin for expression in Escherichia coli. After purification and refolding, the fusion protein His(6)-TEV-eppin was digested with TEV protease to remove the His(6)-tag and was further purified by NTA-Ni(2+) affinity chromatography. Using this procedure, 2 mg of eppin without a His(6)-tag was isolated from 1 l of culture with a purity of >95%. The immunogenicity of the eppin was characterized using male Balb/c mice.

Effects of L-arginine on refolding of lysine-tagged human insulin-like growth factor 1 expressed in Escherichia coli

Insulin-like growth factor 1 (IGF1), a therapeutic protein, is highly homologous to proinsulin in 3-dimensional structure. To highly express IGF1 in recombinant Escherichia coli, IGF1 was engineered to be fused with the 6-lysine tag and ubiquitin at its N-terminus (K6Ub-IGF1). Fed-batch fermentation of E. coli TG1/pAPT-K6Ub-IGF1 resulted in 60.8 g/L of dry cell mass, 18% of which was inclusion bodies composed of K6Ub-IGF1. Subsequent refolding processes were conducted using accumulated inclusion bodies. An environment of 50 mM bicine buffer (pH 8.5), 125 mM L-arginine, and 4 °C was chosen to optimize the refolding of K6Ub-IGF1, and 240 mg/L of denatured K6Ub-IGF1 was refolded with a 32% yield. The positive effect of L-arginine on K6Ub-IGF1 refolding might be ascribed to preventing unfolded K6Ub-IGF1 from undergoing self-aggregation and thus increasing its solubility. The simple dilution refolding, followed by cleavage of the fusion protein by site-specific UBP1 and chromatographic purification of IGF1, led production of authentic IGF1 with 97% purity and an 8.5% purification yield, starting from 500 mg of inclusion bodies composed of K6Ub-IGF1, as verified by various analytical tools, such as RP-HPLC, CD spectroscopy, MALDI-TOF mass spectrometry, and Western blotting. Thus, it was confirmed that L-arginine with an aggregation-protecting ability could be applied to the development of refolding processes for other inclusion body-derived proteins.

Biomimetic engineering of modular bispecific antibodies for biomolecule immobilization

Modular bispecific antibodies (BsAb's) that interact directly with a gold surface were engineered for immobilization on biosensing devices. The BsAb's consist of the variable fragments of antigold and antilysozyme antibodies connected via one of three linkers derived from naturally occurring proteins. The BsAb's were bound tightly to both the gold surface and to lysozyme, thus functioning as interface molecules between lysozyme and the gold surface without a substantial loss of antigen-binding activity. The antigen-binding capacity (the ratio of the amount of immobilized lysozyme to the amount of immobilized BsAb) on the gold surface reached 82%. An analysis of the correlation between binding capacity and linker characteristics indicated that the presence of a long, rigid linker sequence derived from a cellulase resulted in a higher antigen-binding capacity than did the presence of a long but relatively flexible glycine-rich linker. This result suggests a strategy for designing linkers suitable for BsAb-based biomolecular immobilization.

Characterization of three different single chain antibodies recognizing non-reducing terminal mannose residues expressed in Escherichia coli by an inducible T7 expression system

We previously isolated phage antibodies from a phage library displaying human single chain antibodies (scFvs) by screening with a mannotriose (Man3)-bearing lipid. Of four independent scFv genes originally characterized, 5A3 gene products were purified as fusion proteins such as a scFv-human IgG1 Fc form, but stable clones secreting 1A4 and 1G4 scFv-Fc proteins had never been established. Thus, bacterial expression systems were used to purify 1A4 and 1G4 scFv gene products as soluble forms. Purification of 1A4 and 1G4 scFv proteins from inclusion bodies was also carried out together with purification of 5A3 scFv protein in order to compare their Man3-binding abilities. The present studies demonstrated that 1A4 and 1G4 scFv proteins have a higher affinity for Man3 than 5A3 scFv protein, which may determine whether scFv-Fc proteins expressed in mammalian cells are retained in the ER or secreted. Furthermore, the inhibitory effects of anti-Man3 1G4 scFv and anti-Tn antigen scFv proteins on MCF-7 cell growth were evaluated. Despite the fact that no obvious difference was detected in cell growth, microscopic observations revealed inhibition of foci formation in cells grown in the presence of the anti-carbohydrate scFv proteins. This finding provides a basis for the development of cancer therapeutics.

An anti-Aβ (amyloid β) single-chain variable fragment prevents amyloid fibril formation and cytotoxicity by withdrawing Aβ oligomers from the amyloid pathway

Aβ (amyloid β) immunotherapy has been revealed as a possible tool in Alzheimer's disease treatment. In contrast with complete antibodies, the administration of scFvs (single-chain variable fragments) produces neither meningoencephalitis nor cerebral haemorrhage. In the present study, the recombinant expression of scFv-h3D6, a derivative of an antibody specific for Aβ oligomers, is presented, as well as the subsequent proof of its capability to recover the toxicity induced by the Aβ1–42 peptide in the SH-SY5Y neuroblastoma cell line. To gain insight into the conformational changes underlying the prevention of Aβ toxicity by this antibody fragment, the conformational landscape of scFv-h3D6 upon temperature perturbation is also described. Heating the native state does not lead to any extent of unfolding, but rather directly to a β-rich intermediate state which initiates an aggregation pathway. This aggregation pathway is not an amyloid fibril pathway, as is that followed by the Aβ peptide, but rather a worm-like fibril pathway which, noticeably, turns out to be non-toxic. On the other hand, this pathway is thermodynamically and kinetically favoured when the scFv-h3D6 and Aβ1–42 oligomers form a complex in native conditions, explaining how the scFv-h3D6 withdraws Aβ1–42 oligomers from the amyloid pathway. To our knowledge, this is the first description of a conformational mechanism by which a scFv prevents Aβ-oligomer cytotoxicity.

Acceleration of disulfide-coupled protein folding using glutathione derivatives

Protein folding occurs simultaneously with disulfide bond formation. In general, the in vitro folding of proteins containing disulfide bond(s) is carried out in the presence of redox reagents, such as glutathione, to permit native disulfide pairing to occur. It is well known that the formation of a disulfide bond and the correct tertiary structure of a target protein are strongly affected by the redox reagent used. However, little is known concerning the role of each amino acid residue of the redox reagent, such as glutathione. Therefore, we prepared glutathione derivatives - glutamyl-cysteinyl-arginine (ECR) and arginyl-cysteinyl-glycine (RCG) - and examined their ability to facilitate protein folding using lysozyme and prouroguanylin as model proteins. When the reduced and oxidized forms of RCG were used, folding recovery was greater than that for a typical glutathione redox system. This was particularly true when high protein concentrations were employed, whereas folding recovery using ECR was similar to that of the glutathione redox system. Kinetic analyses of the oxidative folding of prouroguanylin revealed that the folding velocity (K(RCG) = 3.69 × 10(-3) s(-1)) using reduced RCG/oxidized RCG was approximately threefold higher than that using reduced glutathione/oxidized glutathione. In addition, folding experiments using only the oxidized form of RCG or glutathione indicated that prouroguanylin was converted to the native conformation more efficiently in the case of RCG, compared with glutathione. The findings indicate that a positively charged redox molecule is preferred to accelerate disulfide-exchange reactions and that the RCG system is effective in mediating the formation of native disulfide bonds in proteins.

Transient exposure of neonatal mice to neuregulin-1 results in hyperdopaminergic states in adulthood: implication in neurodevelopmental hypothesis for schizophrenia

Neuregulin-1 (NRG1) is implicated in the etiology or pathology of schizophrenia, although its biological roles in this illness are not fully understood. Human midbrain dopaminergic neurons highly express NRG1 receptors (ErbB4). To test its neuropathological role in the neurodevelopmental hypothesis of schizophrenia, we administered type-1 NRG1 protein to neonatal mice and evaluated the immediate and subsequent effects on dopaminergic neurons and their associated behaviors. Peripheral NRG1 administration activated midbrain ErbB4 and elevated the expression, phosphorylation and enzyme activity of tyrosine hydroxylase (TH), which ultimately increased dopamine levels. The hyperdopaminergic state was sustained in the medial prefrontal cortex after puberty. There were marked increases in dopaminergic terminals and TH levels. In agreement, higher amounts of dopamine were released from this brain region of NRG1-treated mice following high potassium stimulation. Furthermore, NRG1-treated mice exhibited behavioral impairments in prepulse inhibition, latent inhibition, social behaviors and hypersensitivity to methamphetamine. However, there were no gross abnormalities in brain structures or other phenotypic features of neurons and glial cells. Collectively, our findings provide novel insights into neurotrophic contribution of NRG1 to dopaminergic maldevelopment and schizophrenia pathogenesis.

A chimera of green fluorescent protein with single chain variable fragment antibody against ginsenosides for fluorescence-linked immunosorbent assay

A chimera of green fluorescent protein extracted from Aequorea coerulescens (AcGFP), a mutant that has been codon optimized for mammalian expression, with single-chain variable fragment (scFv) antibody against ginsenoside Re (GRe-scFv), named fluobody, has been successfully expressed in Escherichia coli (E. coli) to develop simple, speedy, and sensitive fluorescence-linked immunosorbent assay (FLISA). Two chimera proteins were constructed to contain GRe-scFv at the C-terminus of AcGFP (C-fluobody) and at the N-terminus of AcGFP (N-fluobody). These fluobodies were then purified by ion metal affinity chromatography and refolded by stepwise dialysis. The characterization of both fluobodies revealed that C-fluobody was found to be appropriate probe for FLISA as compare with N-fluobody. Furthermore, improvement of limit of detection (LOD) was observed in FLISA using C-fluobody (10 ng/mL) due to its strong fluorescence intensity of AcGFP compared with conventional enzyme-linked immunosorbent assay (ELISA) using parental monoclonal antibody against ginsenoside Re (G-Re), MAb-4G10 (100 ng/mL). Since some steps required in ELISA can be avoided in this present FLISA, speedy and sensitive immunoassay also could be performed using fluobody instead of monoclonal antibody and scFv.

Direct immobilization of gold-binding antibody fragments for immunosensor applications

A novel method that enables antibody fragments to be immobilized on a sensor substrate with a high binding capability using molecular recognition has been developed. Using genetic engineering, we fabricated bispecific recombinant antibody fragments, which consist of two kinds of antibody fragments: a gold antibody fragment and a target molecule antibody fragment. Surface plasmon resonance (SPR) analysis indicated that these gold-binding bispecific antibody fragments bind directly to the gold substrate with high affinity (K(D) approximately 10(-9) M). About 70% of the bispecific antibody fragments immobilized on the gold substrate retained their target protein-binding efficiency. The Sips isotherm was used to assess the heterogeneity in antibody affinity for the bispecific antibody fragments. The results showed that the immobilized bispecific antibody fragments exhibited an increased homogeneity of affinity (K(D)) to target molecules when compared with monospecific antibody fragments immobilized by conventional methods. The use of bispecific antibody fragments to directly immobilize antibody fragments on a solid-phase substrate offers a useful platform for immunosensor applications.

A novel protein refolding system using lauroyl-l-glutamate as a solubilizing detergent and arginine as a folding assisting agent

More than 50 detergents, including acylated amino acid derivatives, were screened for their ability to solubilize and refold recombinant proteins expressed as inclusion bodies. Two model proteins, human interleukin-6 and microbial transglutaminase, were solubilized by these detergents and the solubilized proteins were rapidly diluted for testing their solubilization and refolding effectiveness. Long chain-acylated amino acid derivatives having dicarboxylic acid moieties were found to be superior to others under the conditions tested. In particular, lauroyl-l-glutamate (C12-l-Glu) showed the highest recovery of the native proteins. The effectiveness of dilution refolding was greatly improved by adding aggregation suppressive arginine into the refolding solvents. To gain understanding how this detergent works, interactions between detergents and proteins were examined using spectroscopic and native gel electrophoretic analyses, showing ideal properties for C12-l-Glu as a solubilzing agent, i.e. highly reversible nature of the detergent binding to the model globular proteins and of the conformational changes. These properties most likely have contributed to the effective protein solubilzation and refolding of inclusion bodies using C12-l-Glu and arginine.

Ternary system of solution additives with arginine and salt for refolding of beta-galactosidase

(L)-Arginine hydrochloride (Arg HCl) has been used for protein refolding as a universal aggregation suppressor for monomeric proteins. This paper presents an investigation of the refolding of tetrameric beta-galactosidase (beta-gal) using Arg HCl and other salts. In a binary system using only Arg HCl, the refolding yield of beta-gal increased with increasing concentration up to 0.2 M. However, the refolding yield sharply decreased above this concentration, reaching the level below the control yield of 5% at 0.5 M and near zero above 0.75 M, an observation unexpected from monomeric proteins. In a ternary system using both 0.2 M Arg HCl and another salt, the refolding yield increased up to 1.5-fold higher than that in the binary system. These data indicate that aggregation suppressive effects of protein increase with Arg HCl concentration, but also are deleterious to self-association of the protein. This dual nature of Arg HCl effects may have to be taken into account in its application for refolding of oligomeric proteins.

Production of anti-carbohydrate antibodies by phage display technologies: potential impairment of cell growth as a result of endogenous expression

Anti-mannotriose (Man3) antibodies were previously isolated from a Keio phage library displaying human single chain variable fragments (scFvs) using a neoglycolipid, Man3- dipalmitoylphosphatidylethanolamine. Of three genes constructed, the 5A3 clone was expressed in mouse myeloma NS0 cells as a conjugate with human IgG(1) Fc (scFv-Fc) and characterized (Sakai, K., Shimizu, Y., Chiba, T., Matsumoto-Takasaki, A., Kusada, Y., Zhang, W., Nakata, M., Kojima, N., Toma, K., Takayanagi, A., Shimizu, N., and Fujita-Yamaguchi, Y. (2007) Biochemistry 46, 253-262; Zhang, W., Matsumoto-Takasaki, A., Kusada, Y., Sakaue, H., Sakai, K., Nakata, M., and Fujita-Yamaguchi, Y. (2007) Biochemistry 46, 263-270). Similarly, anti-Le(x) phages were screened from the same library with lacto-N-fucopentaose III (LNFPIII; Le(x))-dipalmitoylphosphatidylethanolamine. Of five phage clones isolated, two scFv genes were constructed to express scFv-Fc proteins in NS0 cells. As was experienced with anti-Man3 scFv-Fc clones, only one anti-LNFPIII clone, 1F12, was successfully produced and purified as an scFv-Fc protein. Although anti-LNFPIII 1F12 and anti-Man3 5A3 scFv-Fc proteins were secreted into media, a decline in scFv-Fc production was observed with both stable clones during early passages. Transient expression of anti-LNFPIII and anti-Man3 scFv-Fc genes in COS-7 cells and subsequent analyses of scFv-Fc protein expression revealed accumulation of translated proteins in the endoplasmic reticulum for scFv-Fc proteins derived from clones that did not survive as stable clones. This report describes the following: (i) isolation of anti-LNFPIII scFv genes; (ii) purification of anti-LNFPIII scFv-Fc proteins from stably and transiently expressed cells; and (iii) extracellular or intracellular localization of two anti-LNFPIII and three anti-Man3 scFv-Fc proteins. The results suggest that expression of anti-Man3 and other anti-carbohydrate antibodies in mammalian cells is disadvantageous for cell growth.

Application of the Fc fusion format to generate tag-free bi-specific diabodies

We previously reported the use of a humanized bi-specific diabody that targets epidermal growth factor receptor and CD3 (hEx3-Db) for cancer immunotherapy. Bacterial expression can be used to express small recombinant antibodies on a large scale; however, their overexpression often results in the formation of insoluble aggregates, and in most cases artificial affinity peptide tags need to be fused to the antibodies for purification by affinity chromatography. Here, we propose a novel method for preparing refined, functional, tag-free bi-specific diabodies from IgG-like bi-specific antibodies (BsAbs) in a mammalian expression system. We created an IgG-like BsAb in which bi-specific diabodies were fused to the human Fc region via a designed human rhinovirus 3C (HRV3C) protease recognition site. The BsAb was purified by protein A affinity chromatography, and the refined tag-free hEx3-Db was efficiently produced from the Fc fusion format by protease digestion. The tag-free hEx3-Db from the Fc fusion format showed a greater inhibition of cancer growth than affinity-tagged hEx3-Db prepared directly from Chinese hamster ovary cells. We also applied our novel method to another small recombinant antibody fragment, hEx3 single-chain diabody (hEx3-scDb), and demonstrated the versatility and advantages of our proposed method compared with papain digestion of hEx3-scDb. This approach may be used for industrial-scale production of functional tag-free small therapeutic antibodies.

[Optimization of the industrial production of the recombinant precursor of human insulin]

Conditions were found at the analytical level for the solubilization of a recombinant insulin precursor from inclusion bodies in different buffer systems at a wide pH range in the presence of different reducing (dithiothreitol, dithioerythritol) and chaotropic agents (urea, guanidine hydrochloride) and the subsequent renaturation with the use of redox pairs (cysteine-cystine, oxidized glutathione-reduced glutathione, and others). The scaling of the method for the production of the active substance of genetically engineered human insulin has been performed.

Refolding and purification of rhNTA protein by chromatography

RhNTA protein is a new thrombolytic agent which has potential medicinal and commercial value. Protein refolding is a bottleneck for large-scale production of valuable proteins expressed as inclusion bodies in Escherichia coli. The denatured rhNTA protein was refolded by an improved size-exclusion chromatography refolding process achieved by combining an increasing arginine gradient and a decreasing urea gradient (two gradients) with a size-exclusion chromatography refolding system. The refolding of denatured rhNTA protein showed that this method could significantly increase the activity recovery of protein at high protein concentration. The activity recovery of 37% was obtained from the initial rhNTA protein concentration up to 20 mg/mL. After refolding by two-gradient size-exclusion chromatography refolding processes, the refolded rhNTA was purified by ion-exchange and affinity chromatography. The purified rhNTA protein showed one band in SDS-PAGE and the specific activity of purified rhNTA protein was 110,000 U/mg.