Cytoplasmic expression, antibody production, and characterization of the novel zinc finger protein 637

Zinc finger protein 637 (zfp637), belonging to the Kruppel-like protein family, comprises one atypical C(2)H(2) and six consecutive typical zinc finger motifs. Based on the structural characterization of zfp637 and its location in the cell nucleus, we predict that zfp637 might function as a DNA-binding protein to regulate gene transcription. However, the absence of both a purified zfp637 protein and any commercial antibody for detecting it in cells and tissues has limited functional studies of zfp637 to date. Here, we developed and optimized an expression system by fusing zfp637 with glutathione S-transferase (GST) to achieve a maximal yield of soluble GST-zfp637 fusion protein in Escherichia coli BL21(DE3) cells. The yield was about 10 mg/l of the original bacterial culture. The recombinant GST-zfp637 fusion protein was purified and used for polyclonal antibody production in rabbits. In addition, we developed a method to remove the anti-GST antibody component and obtained a highly purified anti-zfp637 antibody, as demonstrated by an enzyme-linked immunosorbent assay. Western blotting showed that the anti-zfp637 antibody recognized not only the recombinant zfp637 protein but also endogenous zfp637 in several cell lines. The protein was localized mainly in the cell nucleus by immunofluorescence and immunohistochemistry. The expression levels of zfp637 mRNA and protein were significantly increased in NIH3T3 cells treated with 200 μM of H(2)O(2) in a time-dependent manner. The recombinant GST-zfp637 fusion protein and our purified anti-zfp637 antibody will help in elucidating the function of zfp637.

Improved recovery of active GST-fusion proteins from insoluble aggregates: solubilization and purification conditions using PKM2 and HtrA2 as model proteins

The glutathione S-transferase (GST) system is useful for increasing protein solubility and purifying soluble GST fusion proteins. However, purifying half of the GST fusion proteins is still difficult, because they are virtually insoluble under non-denaturing conditions. To optimize a simple and rapid purification condition for GST-pyruvate kinase muscle 2 (GST-PKM2) protein, we used 1% sarkosyl for lysis and a 1:200 ratio of sarkosyl to Triton X-100 (S-T) for purification. We purified the GST-PKM2 protein with a high yield, approximately 5 mg/L culture, which was 33 times higher than that prepared using a conventional method. Notably, the GST-high-temperature requirement A2 (GST-HtrA2) protein, used as a model protein for functional activity, fully maintained its proteolytic activity, even when purified under our S-T condition. This method may be useful to apply to other biologically important proteins that become highly insoluble in the prokaryotic expression system.

Expression of soluble proteins in Escherichia coli by linkage with the acidic propiece of eosinophil major basic protein

An expression method has been developed to produce soluble cationic polypeptides in Escherichia coli while avoiding inclusion body deposition. For this technique the recombinant product is linked through a thrombin or factor Xa susceptible bond to the amino-terminal domain of the precursor of eosinophil major basic protein (MBP). This N-terminal domain is strongly acidic and is apparently able to shield eosinophils from the potentially injurious activities of MBP. It was reasoned that constructs of this acidic domain with small heterologous cationic proteins expressed in E. coli could result in soluble expression while preventing trafficking and packaging into insoluble inclusion bodies. This has been demonstrated using four examples: complement C5a, CCL18, fibroblast growth factor-β, and leukemia inhibitory factor, whose isoelectric points range from 8.93 to 9.59. Further general applicability of this technique has been shown by using two different expression systems, one which encodes an amino-terminal oligo-histidine leash, and another that codes for an amino-terminal glutathione-S-transferase. Thus the utility of coupling MAP to cationic polypeptides for the purpose of soluble heterologous protein expression in E. coli has been demonstrated.

The human hGSTA5 gene encodes an enzymatically active protein

BACKGROUND

Of the five human Alpha-class glutathione transferases, expression of hGSTA5 has not been experimentally documented, even though in silico the hGSTA5 sequence can be assembled into a mRNA and translated. The present work was undertaken to determine whether hGSTA5 is functional.

METHODS

Human K562 cells were transfected with the hGSTA5 gene driven by the CMV promoter, and hGSTA5 cDNA was recovered from mature mRNA by reverse transcription. The cDNA was used in bacterial and eukaryotic protein expression systems. The resulting protein, after purification by glutathione affinity chromatography where appropriate, was tested for glutathione transferase activity.

RESULTS

Human K562 cells transfected with the hGSTA5 gene under control of a CMV promoter produced a fully spliced mRNA which, after reverse transcription and expression in E. coli, yielded a protein that catalyzed the conjugation of the lipid peroxidation product 4-hydroxynonenal to glutathione. Similarly, transfection of human HEK-293 cells with the hGSTA5 gene driven by the CMV promoter led to an elevated 4-hydroxynonenal-conjugating activity in the cell lysate. In addition, translation of hGSTA5 cDNA in a cell-free eukaryotic system gave rise to a protein with 4-hydroxynonenal-conjugating activity.

CONCLUSIONS

hGSTA5 can be processed to a mature mRNA which is translation-competent, producing a catalytically active enzyme.

GENERAL SIGNIFICANCE

Because a functional gene would not be maintained in the absence of selective pressure, we conclude that the native hGSTA5 promoter is active but has a spatially or temporally restricted expression pattern, and/or is expressed only under specific (patho)physiological conditions.

Improvement of downstream processing of recombinant proteins by means of genetic engineering methods

The rapid advancement of genetic engineering has allowed to produce an impressive number of proteins on a scale which would not have been achieved by classical biotechnology. At the beginning of this development research was focussed on elucidating the mechanisms of protein overexpression. The appearance of inclusion bodies may illustrate the success. In the meantime, genetic engineering is not only expected to achieve overexpression, but to improve the whole process of protein production. For downstream processing of recombinant proteins, the synthesis of fusion proteins is of primary importance. Fusion with certain proteins or peptides may protect the target protein from proteolytic degradation and may alter its solubility. Intracellular proteins may be translocated by means of fusions with signal peptides. Affinity tags as fusion complements may render protein separation and purification highly selective. These methods as well as similar ones for improving the downstream processing of proteins will be discussed on the basis of recent literature.

Reconstitution of cytochrome b-560 (QPs1) of bovine heart mitochondrial succinate-ubiquinone reductase

The QPs1 subunit of bovine heart mitochondrial succinate-ubiquinone reductase was overexpressed in Escherichia coli DH5 alpha cells as a glutathione S-transferase fusion protein (GST-QPs1) using the expression vector, pGEX/QPs1. The yield of soluble active recombinant GST-QPs1 fusion protein depends on the IPTG concentration, induction growth time, temperature, and medium. Maximum yield of recombinant fusion protein was obtained from cells harvested 3 h postinduction of growth with 0.5 mM IPTG at 27 degrees C in an enriched medium containing betaine and sorbitol. QPs1 is released from the fusion protein by proteolytic cleavage with thrombin. Isolated recombinant QPs1 shows one protein band in SDS-polyacrylamide gel electrophoresis corresponding to subunit III of mitochondrial succinate-ubiquinone reductase. However, partial N-terminal amino acid sequence analysis of recombinant QPs1 shows two extra amino acid residues, glycine and serine, at the N-terminus of mature QPs1, resulting from the recombinant manipulation. When isolated recombinant QPs1 is dispersed in 0.01% dodecyl maltoside, it is in a highly aggregated form with an apparent molecular mass of over 1 million. Recombinant GST-QPs1 contains little cytochrome b-560 heme. However, addition of hemin chloride restores the spectral characteristics of cytochrome b-560. Cytochrome b-560 restoration varies with the amount of hemin used. Maximum reconstitution is obtained when the molar ratio of heme to fusion protein used in the system is 0.6. Reconstituted cytochrome b-560 shows a EPR signal at g = 2.91 which corresponds to one of the EPR signals of cytochrome b-560 in a QPs preparation. When GST-QPs1 with reconstituted cytochrome b-560 is treated with thrombin to cleave GST from QPs1, no change in the absorption and EPR characteristics of cytochrome b-560 is observed, indicating that the bis-histidine ligands of reconstituted cytochrome b-560 are provided by QPs1.

Purification, characterization, and expression of CFTR nucleotide-binding domains

The nucleotide binding domains (NBDs) within CFTR were initially predicted to lie in the cell cytoplasm, and to gate anion permeability through a pore that was present in membrane spanning alpha helices of the overall polypeptide. Our studies designed to characterize CFTR suggest several important features of the isolated nucleotide binding domain. NBD-1 appears to bind nucleotides with similar affinity to the full-length CFTR protein. In solution, the domain contains a high beta sheet content and self-associates into ordered polymers with molecular mass greater than 300,000 Daltons. The domain is very lipophilic, disrupts liposomes, and readily enters the planar lipid bilayer. Clinically important mutations in the domain may disrupt the nucleotide binding capabilities of the protein, either through a direct effect on the nucleotide binding site, or through effects that influence the overall folding of the domain in vitro. Finally, after expression in human epithelial cells (including epithelial cells from a CF patient), the first nucleotide binding domain targets the plasma membrane even in the absence of other constituents of full-length CFTR and mediates anion permeability in these cells.

Production of biologically active recombinant tilapia insulin-like growth factor-II polypeptides in Escherichia coli cells and characterization of the genomic structure of the coding region

Insulin-like growth factor-II (IGF-II) is a fetal growth factor in humans, but has not been clearly identified in fish up to now. For a detailed understanding of the physiological response of fish IGF-II, the first step was to clone tilapia IGF-II cDNA from the brain cDNA library, coding the region of genomic DNA, and also expressing tilapia IGF-II polypeptides from Escherichia coli. Tilapia cDNA sequences total 1,977 bp, and predicted nucleotide sequences and amino acid sequences of tilapia share 77.9% and 90.7% homology identity with rainbow trout IGF-II, respectively. The genomic structure of the tilapia prepro-IGF-II coding region is very difficult to sequence in mammals and birds. The cloned tilapia IGF-II gene coding region appears much more complex than in other vertebrates. In tilapia IGF-II, the first coding exon I encoding part of the signal peptide sequence is 25 amino acids shorter than the first coding exon of mammals and birds. The other 23 amino acids of the signal peptide, and the first amino acids of the B domain and C domain are encoded by tilapia coding exon 2. The C, A, and D domains, and the first 20 amino acids of the E peptide are encoded by tilapia coding exon 3. The other E peptides and the 3' untranslated region (UTR) region are encoded by tilapia coding exon 4. These data show that the IGF-II genes have significantly differing structures in vertebrate evolution, and there are differences of interrupting introns in the IGF-I genomic structure compared with mammals. To obtain recombinant biologically active polypeptides, tilapia IGF-II B-C-A-D domains were amplified using the polymerase chain reaction (PCR), then ligated with glutathione S-transferase (GST, pGEX-2T vector). Tilapia recombinant IGF-II protein was purified and characterized in E. coli. The fusion protein was also digested with thrombin and appeared as a recombinant IGF-II polypeptide single band with a molecular mass of 7 kD. The recombinant tilapia IGF-II protein biological function was measured by stimulation of [3H]thymidine incorporation. The assay concentration was set up from 0 to 120 nM to stimulate tilapia ovary cell line (TO-2) significantly to uptake thymidine. The results suggest that the recombinant IGF-II protein was dose dependent.

Conformational stability of pGEX-expressed Schistosoma japonicum glutathione S-transferase: a detoxification enzyme and fusion-protein affinity tag

A glutathione S-transferase (Sj26GST) from Schistosoma japonicum, which functions in the parasite's Phase II detoxification pathway, is expressed by the Pharmacia pGEX-2T plasmid and is used widely as a fusion-protein affinity tag. It contains all 217 residues of Sj26GST and an additional 9-residue peptide linker with a thrombin cleavage site at its C-terminus. Size-exclusion HPLC (SEC-HPLC) and SDS-PAGE studies indicate that purification of the homodimeric protein under nonreducing conditions results in the reversible formation of significant amounts of 160-kDa and larger aggregates without a loss in catalytic activity. The basis for oxidative aggregation can be ascribed to the high degree of exposure of the four cysteine residues per subunit. The conformational stability of the dimeric protein was studied by urea- and temperature-induced unfolding techniques. Fluorescence-spectroscopy, SEC-HPLC, urea- and temperature-gradient gel electrophoresis, differential scanning microcalorimetry, and enzyme activity were employed to monitor structural and functional changes. The unfolding data indicate the absence of thermodynamically stable intermediates and that the unfolding/refolding transition is a two-state process involving folded native dimer and unfolded monomer. The stability of the protein was found to be dependent on its concentration, with a delta G degree (H2O) = 26.0 +/- 1.7 kcal/mol. The strong relationship observed between the m-value and the size of the protein indicates that the amount of protein surface area exposed to solvent upon unfolding is the major structural determinant for the dependence of the protein's free energy of unfolding on urea concentration. Thermograms obtained by differential scanning microcalorimetry also fitted a two-state unfolding transition model with values of delta Cp = 7,440 J/mol per K, delta H = 950.4 kJ/mol, and delta S = 1,484 J/mol.

Interaction between cystic fibrosis transmembrane conductance regulator and outwardly rectified chloride channels

We have previously described a protocol for the simultaneous isolation and reconstitution of a protein kinase A (PKA)-sensitive outwardly rectified chloride channel (ORCC) and the cystic fibrosis transmembrane conductance regulator (CFTR) from bovine tracheal epithelium. Immunoprecipitation of CFTR from this preparation prevented PKA activation of the ORCC, suggesting that CFTR regulated the ORCC and that this regulatory relationship was preserved throughout the purification procedure. We now report the purification of CFTR from bovine tracheal epithelia and the purification of a CFTR conduction mutant (G551D CFTR) from retrovirally transduced mouse L cells using a combination of alkali stripping, Triton-X extraction, and immunoaffinity chromatography. Immunopurified CFTR proteins were reconstituted in the absence and presence of ORCC. To test the hypothesis that only functional CFTR can support activation of ORCC by PKA and ATP, we used an inhibitory anti-CFTR505-511 peptide antibody or G551D CFTR. When anti-CFTR505-511 peptide antibodies were present prior to the addition of PKA and ATP, activation of both the ORCC and CFTR was prevented. If the antibody was added after activation of the ORCC and CFTR Cl- channels by PKA and ATP, only the CFTR Cl- channel was inhibited. When ORCC and G551D CFTR were co-incorporated into planar bilayers, only the ORCC was recorded and this channel could not be further activated by the addition of PKA and ATP. Thus, functional CFTR is required for activation of the ORCC by PKA and ATP. We also tested the hypothesis that PKA activation of ORCC was dependent on the extracellular presence of ATP. We added ATP on the presumed extracellular side of the lipid bilayer under conditions where it was not possible to activate the ORCC, i.e. in the presence of inhibitory anti-CFTR505-511 antibody or G551D CFTR. In both cases the ORCC regained PKA sensitivity. Moreover, the addition of hexokinase + glucose to the extracellular side prevented activation of the ORCCs by PKA and ATP in the presence of CFTR. These experiments confirm that both the presence of CFTR as well as the presence of ATP on the extracellular side is required for activation of the ORCC by PKA and ATP.

Cloning, gene sequencing, and expression of the small molecular mass ubiquinone-binding protein of mitochondrial ubiquinol-cytochrome c reductase

The cDNA encoding QPc-9.5 kDa (subunit VII) of bovine heart mitochondrial ubiquinol-cytochrome c reductase was cloned and sequenced. This cDNA is 665 base pairs long with an open reading frame of 246 base pairs that encodes an 81-amino acid mature QPc-9.5 kDa. The insert contains 395 base pairs of a 3'-noncoding sequence with a poly(A) tail. The amino acid sequence of QPc-9.5 kDa deduced from this nucleotide sequence is the same as that obtained by protein sequencing except that residue 61 is tryptophan instead of cysteine. The QPc-9.5 kDa was overexpressed in Escherichia coli JM109 cells as a glutathione S-transferase fusion protein (GST-QPc) using the expression vector, pGEX/QPc. The yield of soluble active recombinant GST-QPc fusion protein depends on the induction growth time, temperature, and medium. Maximum yield of recombinant fusion protein was obtained from cells harvested 3 h postinduction of growth at 27 degrees C on LB medium containing betaine and sorbitol. QPc-9.5 kDa was released from the fusion protein by proteolytic cleavage with thrombin. Isolated recombinant QPc-9.5 kDa showed one protein band in SDS-polyacrylamide gel electrophroesis corresponding to subunit VII of mitochondrial ubiquinol-cytochrome c reductase. Although the isolated recombinant QPc-9.5 kDa is soluble in aqueous solution, it is in a highly aggregated form, with an apparent molecular mass of over 1 million. Addition of detergent deaggreates the isolated protein to the monomeric state, suggesting that the recombinant protein exists as a hydrophobic aggregation in aqueous solution. The recombinant QPc-9.5 kDa binds ubiquinone and shows a spectral blue shift. Upon titration of the recombinant protein with ubiquinone, a saturation behavior is observed, suggesting that the binding is specific and that the recombinant protein may be in the functionally active state.

Chromatography in the downstream processing of biotechnological products

Chromatography techniques are essential for the isolation and purification of most of the high value products of modern biotechnology. The economically sensible and technically satisfactory downstream processing of a therapeutic protein, usually involves a number of chromatographic steps. Its development and optimization require considerable knowledge of the various physico-chemical and engineering aspects of biochemical chromatography. This review addresses the various modes of chromatography and the design of chromatographic separation processes from a biotechnologist's point of view. Strategies for optimizing the structure of the downstream process are outlined and scaling up consideration are discussed. The importance of the different chromatographic methods in research and development is estimated in an analysis of protein purification schemes recently published in the literature. Finally, examples of the application of chromatographic procedures for process scale product purification in the biotechnological industry are given.

Characterization of a homolog of human bone morphogenetic protein 1 in the embryo of the sea urchin, Strongylocentrotus purpuratus

A cDNA clone encoding a protein homologous to human bone morphogenetic protein 1 (huBMP1) was isolated from a sea urchin embryo cDNA library. This sea urchin gene, named suBMP, encodes a protein of M(r) of 72 × 10(3). The deduced amino acid sequence of suBMP shares 72% sequence similarity (55% identity) with that of huBMP1. Like huBMP1 it also contains an N-terminal metalloendoprotease domain that shares sequence similarity with the astacin protease from crayfish, a C-terminal domain that is similar to the repeat domain found in C1r or C1s serine proteases, and an EGF-like segment. Although suBMP mRNA was detectable at a low level in the unfertilized egg, maximal expression of mRNA was observed at hatched blastula stage, with only a modest decrease in level at later stages of development. In situ hybridization studies revealed that suBMP mRNA is found in both ectodermal and primary mesenchyme cells in hatched blastula-stage embryos. Maximal expression of suBMP was observed at mesenchyme blastula, just before the onset of primitive skeleton (spicule) formation. SuBMP was found by immunoelectronmicroscopy in all cell types in late gastrula stage embryos. The antibody gold particles appeared in small clusters in the cytoplasm, on the surface of the cells and within the blastocoel. This distribution of suBMP, coupled with the finding that it was associated with membranes but was released by sodium carbonate treatment, suggests that the protein is secreted, and subsequently associates with a cell surface component. Two models for the possible function of suBMP in spiculogenesis in the sea urchin embryo are discussed.