Production, purification and characterization of recombinant human interferon gamma

Tagging Recombinant Proteins to Enhance Solubility and Aid Purification

Protein fusion technology has had a major impact on the efficient production and purification of individual recombinant proteins. The use of genetically engineered affinity and solubility-enhancing polypeptide "tags" has a long history, and there is a considerable repertoire of these that can be used to address issues related to the expression, stability, solubility, folding, and purification of their fusion partner. In the case of large-scale proteomic studies, the development of purification procedures tailored to individual proteins is not practicable, and affinity tags have become indispensable tools for structural and functional proteomic initiatives that involve the expression of many proteins in parallel. In this chapter, the rationale and applications of a range of established and more recently developed solubility-enhancing and affinity tags is described.

Proteomics analysis of host cell proteins after immobilized metal affinity chromatography: Influence of ligand and metal ions

Different degrees of protein purity have been observed in immobilized metal affinity chromatography ranging from extremely high purity to moderate and low purity. It has been hypothesized that the host cell protein composition and the metal ligands are factors governing the purity of a protein obtained after immobilized metal affinity chromatography (IMAC). Ni nitrilotriacetic acid (NTA) has become the first choice for facile His-tagged protein purification, but alternative ligands such as iminodiacetic acid (IDA) with other immobilized metal ions such as Zn, Cu and Co are valuable options when the expected purity or binding capacity is not reached. Especially Cu and Zn are very attractive, due to their reduced environmental and safety concerns compared to Ni. Co and Zn are more selective than Ni and Cu. This increased selectivity comes at the cost of weaker binding. In this work, the influence of ligand choice on protein purity after IMAC was evaluated by several methods, including peptide mapping. His-tagged GFP was used as model protein. We found that host cell protein (HCP) content varies drastically between ligands, as IDA eluates generally showing higher HCP concentrations than NTA. The relative content of the key amino acids His, Cys and Trp in the sequence of the co-eluted protein does not suffice to explain co-eluting propensity. The co-elution of HCPs is mostly influenced by metal binding clusters on the protein surface and not by total content or surface concentration of metal interacting amino acids. Prediction of co-elution is not dependent on these clusters alone, due to protein-protein interactions, indicted by a relative low metal binding cluster score but high co-elution propensity and in a lot of cases these proteins are often part of complex such as ribosome and chaperones. The different co-eluting proteins were presented by a heatmap with a dendrogram. Ward's linkage method was used to calculate the distance between groups of co-eluting proteins. Clustering of co-eluting HCPs was observed according to ligand and by metal ions, with Zn and Co forming one cluster and Ni and Cu another. The co-elution of host cell proteins can be explained by clusters of metal interacting amino acids on the protein surface and by protein-protein interactions. While Ni NTA still appears to be highly advantageous, it might not be the cure-all for all applications.

Novel IFNγ homologue identified in Nile tilapia (Oreochromis niloticus) links with immune response in gills under different stimuli

Interferon gamma (IFN-γ) has important roles in both innate and adaptive immune responses. This cytokine plays a very important role in defining Th1 immune response in all vertebrates. In the present study, we identified and isolated for the first time the gene coding for Nile tilapia (Oreochromis niloticus) IFNγ from spleen lymphocytes. The isolated tilapia IFNγ has between 24 and 62% of amino acid identity as compared to reported sequences for other teleost fishes. It has close phylogenetic relationships with IFNγ molecules belonging to the group of Perciforms and presents the typical structural characteristics of gamma interferon molecules. The tissue expression analysis showed that IFNγ is expressed constitutively in head kidney, skin, intestine, muscle and brain. Its expression was not detected in gills by conventional RT-PCR. However, under conditions of stimulation with Poly I:C and LPS, IFNγ expression was up-regulated in gills after 24 h post-stimulation. IFNγ expression was also induced in gills 24 h after Edwardsiella tarda infection suggesting its important role in immunity against intracellular bacteria. The recombinant protein produced in Escherichia coli induced Mx gene transcription in head kidney primary culture cells. These results are the first steps to characterize the role of tilapia IFNγ in the defense against pathogens in tilapia. Furthermore, the isolation of this molecule provides a new tool to characterize the cellular immune response to various stimuli in this organism.

Tagging Recombinant Proteins to Enhance Solubility and Aid Purification

Protein fusion technology has had a major impact on the efficient production and purification of individual recombinant proteins. The use of genetically engineered affinity and solubility-enhancing polypeptide "tags" has increased greatly in recent years and there now exists a considerable repertoire of these that can be used to solve issues related to the expression, stability, solubility, folding, and purification of their fusion partner. In the case of large-scale proteomic studies, the development of purification procedures tailored to individual proteins is not practicable, and affinity tags have therefore become indispensable tools for structural and functional proteomic initiatives that involve the expression of many proteins in parallel. Here, the rationale and applications of a range of established and more recently developed solubility-enhancing and affinity tags is described.

Two variables dominating the retention of intact proteins under gradient elution with simultaneous ultrafast high-resolution separation by hydrophobic interaction chromatography

The retention of proteins under gradient elution in HIC is dominated by two variables of steady and migration regions.

Immobilized metal ion affinity chromatography: a review on its applications

After 35 years of development, immobilized metal ion affinity chromatography (IMAC) has evolved into a popular protein purification technique. This review starts with a discussion of its mechanism and advantages. It continues with its applications which include the purification of histidine-tagged proteins, natural metal-binding proteins, and antibodies. IMAC used in conjunction with mass spectroscopy for phosphoprotein fractionation and proteomics is also covered. Finally, this review addresses the developments, limitations, and considerations of IMAC in the biopharmaceutical industry.

Expression of recombinant human interferon-γ with antiviral activity in the bi-cistronic baculovirus-insect/larval system

A bi-cistronic baculovirus-insect/larval system containing a polyhedron promoter, an internal ribosome entry site (IRES), and an egfp gene was developed as a cost-effective platform for the production of recombinant human interferon gamma (rhIFN-γ). There was no significant difference between the amounts of rhIFN-γ produced in the baculovirus-infected Spodoptera frugiferda 21 cells grown in serum-free medium and the serum-supplemented medium, while the Trichoplusia ni (T. ni) and Spodoptera exigua (S. exigua) larvae afforded rhIFN-γ amounting to 1.08±0.04 and 9.74±0.35 µg/mg protein respectively. The presence of non-glycosylated and glycosylated rhIFN-γ was confirmed by immunoblot and lectin blot. The immunological activity of purified rhIFN-γ, with 96% purity by Nickel (II)-nitrilotriacetic acid (Ni-NTA) affinity chromatography, was similar to that commercially available. Moreover, the rhIFN-γ protein from T. ni had more potent antiviral activity. These findings suggest that this IRES-based expression system is a simple and inexpensive alternative for large-scale protein production in anti-viral research.

Tagging recombinant proteins to enhance solubility and aid purification

Protein fusion technology has enormously facilitated the efficient production and purification of individual recombinant proteins. The use of genetically engineered affinity and solubility-enhancing polypeptide "tags" has increased greatly in recent years and there now exists a considerable repertoire of these that can be used to solve issues related to the expression, stability, solubility, folding, and purification of their fusion partner. In the case of large-scale proteomic studies, the development of purification procedures tailored to individual proteins is not practicable, and affinity tags have therefore become indispensable tools for structural and functional proteomic initiatives that involve the expression of many proteins in parallel. Here, the rationale and applications of a range of established and more recently developed solubility-enhancing and affinity tags are outlined.

Kinetic studies of recombinant human interferon-gamma expression in continuous cultures of E. coli

A series of continuous cultures was performed to understand the product formation kinetics of recombinant human interferon gamma (rhIFN-gamma) in Escherichia coli at different dilution rates ranging from 0.1 to 0.3 h(-1) in different media. A T7 promoter-based vector was used for expression of IFN-gamma in E. coli BL21 (DE3) cells. The recombinant protein was produced as inclusion bodies, thus allowing a rapid buildup of rhIFN-gamma inside the cell, with the specific product yield (Y(p/X)) reaching a maximum value of 182 mg g(-1) dry cell weight (DCW). In all the media tested, the specific product formation rate (q(p)) was found to be strongly correlated with the specific growth rate (mu), demonstrating the growth-associated nature of product formation. The q(p) values show no significant decline with time postinduction, even though the recombinant protein has been over produced inside the cell. The maximum q(p) level of 75.5 mg g(-1) h(-1) was achieved at the first hour of induction at the dilution rate of 0.3 h(-1). Also, this correlation between q(p) and mu was not critically dependent on media composition, which would made it possible to grow cells in defined media in the growth phase and then push up the specific growth rate just before induction by pulse addition of glucose and yeast extract. This would ensure the twin objectives of high biomass and high specific productivities, leading to high volumetric product concentration.

Enhancement of human gamma-interferon production in recombinant E. coli using batch cultivation

Development of inexpensive and simple culture media and appropriate induction conditions are always favorable for industry. In this research, chemical composition and stoichiometric data for gamma-interferon production and recombinant Escherichia coli growth were used in order to achieve a simple medium and favorable induction conditions. To achieve this goal, the effects of medium composition and induction conditions on the production of gamma-interferon were investigated in batch culture of E. coli BL21 (DE3) [pET3a-ifngamma]. These conditions were considered as suitable conditions for the production of gamma-interferon: 2.5x M9 medium, supplemented with a mixture of amino acids (milligram per liter), including glutamic acid 215, aspartic acid 250, lysine 160, and phenylalanine 90, and induction at late-log phase (OD(600) = 4.5). Under these conditions, dry cell weight of 6 +/- 0.2 g/l and gamma-interferon concentration of 2.15 +/- 0.1 g/l were obtained. Later, without changing the concentration ratio of amino acids and glucose, the effect of increase in the primary glucose concentration on productivity of gamma-interferon was investigated. It was found that 25 g/l glucose will result in maximum attainable biomass and recombinant human gamma-interferon. At improved conditions, a dry cell weight of 14 +/- 0.2 g/l, concentration and overall productivity of gamma-interferon 4.2 +/- 0.1 g/l and 420 +/- 10 mg/l h, respectively, were obtained.

Periplasmic expression and recovery of human interferon gamma in Escherichia coli

A synthetic human interferon gamma (hIFN-gamma) gene was fused to SP1 and SP3, two Sec-dependent artificial signal peptides to transport the hIFN-gamma to the periplasm of Escherichia coli BL21-SI. The processing efficiency of both SP1-hIFN-gamma and SP3-hIFN-gamma was dependent on the culture medium as well as the post-induction temperature. Both precursors were processed completely when cells were cultured using minimal medium and a post-induction temperature of 32.5 degrees C, and only the processed hIFN-gamma was detected. The SP3 signal peptide was more efficient than SP1 for the secretion of hIFN-gamma. Sixty percent of the total hIFN-gamma was secreted to the periplasm using the SP3 signal peptide and a post-induction temperature of 20 degrees C. Using Tris-sucrose-dithiothreitol (TSD) hypertonic buffer, the periplasmic soluble hINF-gamma was recovered with a purity of 85%.

Large-scale purification of human granulocyte-macrophage colony-stimulating factor expressed in Bombyx mori pupae

Human granulocyte-macrophage colony-stimulating factor (hGM-CSF) acts on many different kinds of cells, including monocytes, macrophages, granulocytes, eosinophils, and multipotential stem cells. To explore further explore pharmaceutical action, we expressed hGM-CSF by the Bombyx mori nucleopolyhedrovirus expression system in silkworm pupae. However, purifying recombinant proteins from silkworm pupae on a large scale has been a big challenge. To establish purification methods suitable for mass production, we tried two crude preparation methods: (NH4)2SO4 fractional precipitation and isoelectric precipitation with a combination of gel filtration and ion-exchange chromatography. The isoelectric precipitation method was found to be more efficient. With this method, we eventually obtained approx 11.7 mg of 95% pure product from 1000 g of infected silkworm pupae. The recovery of purified protein was greatly increased, by approx 40%, compared with the other method. The biologic activity of this protein was determined up to 9.0 x 106 colony-forming units/mg in the final purified product.

Improving purification of recombinant human interferon γ expressed in Escherichia coli; effect of removal of impurity on the process yield

Process development and optimization studies were performed in order to improve the purification process of (rhIFN-gamma). The objective was to generate material with higher purity and quantity. An in-process control screening was developed to obtain the optimal condition for column chromatographic purification by measuring LPS, nucleic acids, rhIFN- gamma, monomer and its covalent dimers. A new resin screening method was applied to select optimal resin for each of the chromatographic columns. The resulting process used Butyl and Q-Sepharose, refolding and SP-Sepharose for purification of IFN-gamma. Effects of different process conditions such as cell lysis, removal of impurity and oxygen concentration were evaluated. Removal of impurities was evaluated by washing of inclusion bodies with 1% Triton X-100 and 3M urea and different chromatography steps. The results reveal that Triton removed about 43% of the LPS but urea had no effect on removal of nucleic acids and LPS. Further analysis show that removal of impurities by column chromatography decreases aggregation and increases the process yield. Oxygen concentration was identified as parameter that could have a significant impact on covalent dimers formation, as an unacceptable pharmaceutical form of rhIFN-gamma. On the basis of small-scale studies, optimum operating conditions were chosen and the purification process was successfully scaled-up to a pilot scale process with step yield and product quality that were better than previous reports.

Increased yield of high purity recombinant human interferon-gamma utilizing reversed phase column chromatography

Increasing therapeutic applications for recombinant human interferon-gamma (rhIFN-gamma), an antiviral proinflammatory cytokine, has broadened interest in optimizing methods for its production and purification. We describe a reversed phase chromatography (RPC) procedure using Source-30 matrix in the purification of rhIFN-gamma from Escherichia coli that results in a higher yield than previously reported. The purified rhIFN-gamma monomer from the RPC column is refolded in Tris buffer. Optimal refolding occurs at protein concentrations between 50 and 100 microg/ml. This method yields greater than 90% of the dimer form with a yield of 40 mg/g cell mass. Greater than 99% purity is achieved with further purification over a Superdex G-75 column to obtain specific activities of from 2 x 10(7) to 4 x 10(7)IU/mg protein as determined via cytopathic antiviral assay. The improved yield of rhIFN-gamma in a simple chromatographic purification procedure promises to enhance the development and therapeutic application of this biologically potent molecule.

The effect of the hexahistidine-tag in the oligomerization of HSC70 constructs

The hexahistidine is a fusion tag used for the isolation of proteins via an immobilized metal-ion affinity chromatography (IMAC). In the present study, we have purified and analyzed two constructs of the heat shock protein HSC70 in the presence or the absence of the His-tag (C30WT-His(+)/C30WT and C30DeltaL-His(+)/C30DeltaL). The oligomerization properties of the constructs were analyzed by size exclusion chromatography (SEC) and analytical ultracentrifugation (AU). Results from SEC analysis indicated that the His-tag promotes the dimerization of C30DeltaL-His(+) but has no effect on the elution profile of C30WT-His(+), compared to their respective untagged forms C30DeltaL and C30WT. These observations were also confirmed by AU analysis which indicates that C30DeltaL is stabilized in the dimeric form in the presence of the His-tag. These results emphasize the need to remove the His-tag before structural characterization of some recombinant proteins.

Refolding and purification of interferon-gamma in industry by hydrophobic interaction chromatography

A new technology for renaturation with simultaneous purification of the recombinant human interferon-gamma (rhIFN-gamma) in downstream of biotechnology is presented. The strategies to develop the new technology in industry scale were suggested. Based on chemical equilibrium and molecular interactions, the principle of rhIFN-gamma refolding by HPHIC was described. The kind of stationary and mobile phases were evaluated and found the former to contribute to the rhIFN-gamma refolding more than the latter. The extract containing the rhIFN-gamma in gram scale in 7.0 mol L(-1) guanidine hydrochloride solution of 700 mL was directly pumped into a unit of simultaneous renaturation and purification of proteins (USRPP, 10 x 300 mm i.d.) packed by small particle packings of hydrophobic interaction chromatography and a satisfactory recovery of bioactivity and mass of the rhIFN-gamma was obtained. With flow rate 100 mL min(-1) and a gradient elution by only one step in 4h, the purity and specific bioactivity approach to 95% and 8.7 x 10(7) IU(-1) mg, respectively. To evaluate the goodness of the presented new technology in this study, a usual method with the renaturation by dilution method firstly and then purification with a series of LC in literature was employed to compare with each other. The obtained result in terms of purity, recoveries of mass and bioactivity, cost time as well as expenses, the former is much better than the latter. Comparing the total bioactivity of rhIFN-gamma in the extract before to that after the renaturation by the USRPP, the total bioactivity of rhIFN-gamma increased 62-fold.

Establishment of a Large-Scale Purification Procedure for Purified Recombinant Bovine Interferon-.TAU. Produced by a Silkworm-Baculovirus Gene Expression System

We developed a procedure for the large-scale purification of bovine interferon-tau (boIFN-tau) by means of a silkworm-baculovirus gene expression system. Recombinant boIFN-tau (rboIFN-tau) was efficiently produced in the silkworm infected with boIFN-tau cDNA recombinant baculovirus and accumulated in the haemolymph. To establish a purification method suitable for mass production, we tried three crude purification methods, namely, an acidification and neutralization treatment (ANT), silica gel column chromatography (SGCC), and Blue sepharose column chromatography (BSCC) with a combination of Q-sepharose (QSC) and chelating sepharose column chromatographies (CSCC). As a result, the acidification and neutralization treatment was found to be the most efficient and cost effective. With this combination, we obtained 91% pure products. To confirm the applicability of the procedure for mass production, we inoculated 100 silkworms with the recombinant virus, and recovered about 4.55 mg (1.26 x 10(8)U/mg) of 91% pure rboIFN-tau by means of a combination of the ANT, followed by QSC and CSCC.

Glycation and post-translational processing of human interferon-gamma expressed in Escherichia coli

Until recently, nonenzymatic glycosylation (glycation) was thought to affect the proteins of long living eukaryotes only. However, in a recent study (Mironova, R., Niwa, T., Hayashi, H., Dimitrova, R., and Ivanov, I. (2001) Mol. Microbiol. 39, 1061-1068), we have shown that glycation takes place in Escherichia coli as well. In the present study, we demonstrate that the post-translational processing (proteolysis and covalent dimerization) observed with cysteineless recombinant human interferon-gamma (rhIFN-gamma) is tightly associated with its in vivo glycation. Our results show that, at the time of isolation, rhIFN-gamma contained early (but not advanced) glycation products. Using reverse phase high performance liquid chromatography in conjunction with fluorescence measurements, enzyme-linked immunosorbent assay, and mass spectrometry, we found that advanced glycation end products arose in rhIFN-gamma during storage. The latter were identified mainly in the Arg/Lys-rich C terminus of the protein, which was also the main target of proteolysis. Mass spectral analysis and N-terminal sequencing revealed four major (Arg140/Arg141, Phe137/Arg138, Met135/Leu136, and Lys131/Arg132) and two minor (Lys109/Ala110 and Arg90/Asp91) cleavage sites in this region. Tryptic peptide mapping indicated that the covalent dimers of rhIFN-gamma originating during storage were formed mainly by lateral cross-linking of the monomer subunits. Antiviral assay showed that proteolysis lowered the antiviral activity of rhIFN-gamma, whereas covalent dimerization completely abolished it.

Current and prospective applications of metal ion-protein binding

Since immobilized metal ion affinity chromatography (IMAC) was first introduced, several variants of this method and many other metal affinity-based techniques have been devised. IMAC quickly established itself as a highly reliable purification procedure, showing rapid expansion in the number of preparative and analytical applications while not remaining confined to protein separation. It was soon applied to protein refolding (matrix-assisted refolding), evaluation of protein folding status, protein surface topography studies and biosensor development. In this review, applications in protein processing are described of IMAC as well as other metal affinity-based technologies.

Relative position of the hexahistidine tag effects binding properties of a tumor-associated single-chain Fv construct

Hexahistidine tag (His-tag) is the most widely used tag for affinity purification of recombinant proteins for their structural and functional analysis. In the present study, single chain Fv (scFv) constructs were engineered form the monoclonal antibody (MAb) CC49 which is among the most extensively studied MAb for cancer therapy. For achieving efficient purification of scFvs by immobilized metal-ion affinity chromatography (IMAC), a His-tag was placed either at the C-terminal (scFv-His6) or N-terminal (His6-scFv) of the coding sequence. Solid-phase radioimmunoassay for scFv-His6 showed only 20-25% binding whereas both His6-scFv and scFv (no His-tag) showed 60-65% binding. Surface plasmon resonance studies by BIAcore revealed the binding affinity constant (KA) for His6-scFv and scFv as 1.19 x 10(6) M(-1) and 3.27 x 10(6) M(-1), respectively. No K(A) value could be calculated for scFv-His6 due to poor binding kinetics (kon and koff). Comparative homology modeling for scFv and scFv-His6 showed that the C-terminal position of the His-tag partially covered the antigen-binding site of the protein. The study demonstrates that the C-terminal position of His-tag on the CC49 scFv adversely affects the binding properties of the construct. The results emphasize the importance of functional characterization of recombinant proteins expressed with purification tags.

Immobilised metal affinity chromatography of beta-galactosidase from unclarified Escherichia coli homogenates using expanded bed adsorption

The development of an expanded bed process for the direct extraction and partial purification of beta-galactosidase from unclarified Escherichia coli homogenates using its natural affinity for metal loaded STREAMLINE Chelating is described. Small packed beds were used to determine the effect of chelated metal ion (Cu2+, Ni2+, Co2+ or Zn2+), loading pH and ionic strength on the selective binding capacity, and recovery of beta-galactosidase from clarified homogenates. An elution protocol was developed using the competitive displacer, imidazole, to recover beta-galactosidase in 87% yield and 3.4-fold purification. These results were then used to develop a separation for the recovery of beta-galactosidase from unclarified homogenates in a 2.5-cm diameter expanded bed. Although Ni2+ loaded STREAMLINE Chelating had a 5% dynamic capacity for beta-galactosidase of just 118 U ml(-1) (0.39 mg ml(-1)), the low capacity was thought to be due to the large size of the target (464,000) relative to the exclusion limit of the macroporous adsorbent. Despite this low capacity, Ni2 STREAMLINE Chelating was used successfully to recover beta-galactosidase from an unclarified homogenate in 86.4% yield and at 5.95-fold purification. The degree of purification relative to a commercial standard, as assessed using the purification factor and sodium dodecyl sulphate-polyacrylamide gel electrophoresis was high suggesting that this pseudo-affinity procedure compared favourably with alternative methods.

Thermal denaturation of human gamma-interferon. A calorimetric and spectroscopic study

The thermal denaturation of a recombinant human gamma-interferon has been studied as a function of pH in the range from 2 to 10 and buffer concentration in the range from 5 to 100 mM by differential scanning calorimetry, circular dichroism, fluorescence, 1H NMR, and biological activity measurements. The thermal transitions are irreversible at high buffer concentrations at all pH values studied, although they are reversible between pH 3.5 and 5.4 at low buffer concentrations. The denaturation enthalpy, DeltaH(Tm), at denaturation temperature Tm was a function of both Tm and the buffer concentration, and this resulted in heat capacity changes decreasing with buffer concentration. When the denaturation enthalpies were corrected for Tm dependence, they did not appear to change versus pH. The denaturation entropies, however, appeared to decrease with pH, leading to a small but appreciable increase in the stability of the protein with pH. The difference between the number of moles of protons stoichiometrically bound to a mole of protein in the native and thermally denatured state, was calculated from the variation of Tm versus pH at each buffer concentration. The values obtained appear to depend on pH alone rather than upon temperature or buffer concentration, a result which agrees with the invariance of the denaturation enthalpies with pH. This dependence was fitted to the titration curve of a group with a pK of 5.4.

Current trends in molecular recognition and bioseparation

Molecular recognition guides the selective interaction of macromolecules with each other in essentially all biological processes. Perhaps the most impactful use of biomolecular recognition in separation science has been in affinity chromatography. The results of the last 26 years, since Cuatrecases, Wilchek and Anfinsen first reported the purification of staphylococcal nuclease, have validated the power of biomolecular specificity for purification. This power has stimulated an explosion of solid-phase ligand designs and affinity chromatographic applications. An ongoing case in point is the purification of recombinant proteins, which has been aided by engineering the proteins to contain Affinity-Tag sequences, such as hexa-histidine for metal-chelate separation and epitope sequence for separation by an immobilized monoclonal antibody. Tag technology can be adapted for plate assays and other solid-phase techniques. The advance of affinity chromatography also has stimulated immobilized ligand-based methods to characterize macromolecular recognition, including both chromatographic and optical biosensor methods. And, new methods such as phage display and other diversity library approaches continue to emerge to identify new recognition molecules of potential use as affinity ligands. Overall, it is tantalizing to envision a continued evolution of new affinity technologies which use the selectivity built into biomolecular recognition as a vehicle for purification, analysis, screening and other applications in separation sciences.

Purification of recombinant human granulocyte-macrophage colony-stimulating factor from the inclusion bodies produced by transformed Escherichia coli cells

Recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF), produced as inclusion bodies in genetically transformed Escherichia coli cells was purified to homogeneity by a three-step chromatographic procedure involving hydrophobic interaction, ion exchange and gel filtration. Each purification step is reproducible and well suited for process-scale operations. The purification process also leads to a significant decrease in DNA and endotoxin levels in the final product. Of the three gel media used, Phenyl Sepharose 6 FF (high sub) was most effective in reducing the DNA content (by a factor of ca. 2000) while Superdex 75 prep grade was more effective for removing endotoxins (reduction factor ca. 15). The recovery of purified rhGM-CSF was 35% by enzyme-linked immunosorbent assay and 70% by a biological assay method. The overall purification factor obtained was about 4.6, which is in the range of those reported for recombinant proteins produced in E. coli as inclusion bodies. The purified rhGM-CSF is an acidic protein (pI = 5.4) and has a specific activity of ca. 3.3 x 10(7) units/mg, which is in excellent agreement with that reported for its natural counterpart. Its monomer molecular mass of 14,605, as determined by electrospray mass spectrometry, corresponds exactly to the mass calculated from its cDNA sequence. Its amino acid composition and partial NH2-terminal sequence (up to seventeen residues) are also identical with those reported for this protein. These and other results confirm the identity of the purified rhGM-CSF with its natural counterpart. However, the results also showed that it is apparently heterogeneous from its NH2-terminal side as it is composed of three polypeptides having Met, Ala and Pro as the NH2-terminal residues in which the intact Met analogue accounts for 60% for the mixture. This heterogeneity does not seem to have any biological significance since the specific activity of the purified rhGM-CSF is identical with that of its natural counterpart.

Refolding and single-step purification of porcine interferon-gamma from Escherichia coli inclusion bodies. Conditions for reconstitution of dimeric IFN-gamma

Recombinant porcine interferon-gamma, overexpressed in Escherichia coli, was found to accumulate in cytoplasmic inclusion bodies. The influence of various physicochemical parameters on refolding was investigated using 6 M guanidine/HCl-solubilised inclusion bodies which had been purified by ultracentrifugation on a sucrose step gradient. It appeared that the yield of reconstitution of denatured protein reached 60-70% under optimum conditions, i.e. at an intermediary guanidine/HCl concentration of 0.5 M and at a protein concentration of 10-20 microM (0 degrees C). Since intermediary guanidine/HCl concentrations at 0.5-1.65 M increasingly promoted off-pathway formation of soluble aggregates and at 0.5-0.2 M progressively promoted precipitation, maximal recovery of biologically active protein required a twofold transition in the surrounding guanidine/HCl concentration (6 M-->0.5 M-->0 M). A single additional size-exclusion chromatographic step yielded a final product that was > 99.5% pure, had specific antiviral activity > 10(7) U/mg protein and contained < or = 25 pg/ml endotoxin. Cross-linking by means of disulfosuccinimidyl tartarate revealed that the refolded protein possessed a dimeric structure. Furthermore, we have characterized three different molecular species of recombinant porcine interferon-gamma that are formed under non-optimal refolding conditions (1 M guanidine/HCl) and that differ from each other in specific activity, size and stability. One of these converts irreversibly into dimeric interferon-gamma in a temperature-dependent manner and is therefore considered as a productive folding intermediate.