Enhanced in vitro refolding of fibroblast growth factor 15 with the assistance of SUMO fusion partner

Enhanced soluble expression of active recombinant human interleukin-29 using champion pET SUMO system

Current research focuses on the soluble and high-level expression of biologically active recombinant human IL-29 protein in Escherichia coli. The codon-optimized IL-29 gene was cloned into the Champion™ pET SUMO expression system downstream of the SUMO tag under the influence of the T7 lac promoter. The expression of SUMO-fused IL-29 protein was compared in E. coli Rosetta 2(DE3), Rosetta 2(DE3) pLysS, and Rosetta-gami 2(DE3). The release of the SUMO fusion partner resulted in approximately 98 mg of native rhIL-29 protein with a purity of 99% from 1 l of fermentation culture. Purified rhIL-29 was found to be biologically active, as evaluated by its anti-proliferation assay. It was found that Champion™ pET SUMO expression system can be used to obtained high yield of biologically active soluble recombinant human protein compared to other expression vector.

Functional expression of a thrombin exosite I inhibitor triabin in Escherichia coli and elucidation of the role of key residues in its inhibitory activity

Triabin, a lipocalin-like thrombin inhibitor from the saliva of the blood-sucking triatomine bug Triatoma pallidipennis, exhibits effective inhibition comparable to hirudin despite binding exclusively at exosite I. Interestingly, it was reported that higher triabin doses would not inhibit thrombin completely, which makes it a promising antithrombotic candidate agent with a larger therapeutic window. However, few structural and functional studies about triabin have been reported in the past three decades, mostly due to the lack of a reliable and practicable recombinant expression technology for this seemingly small protein. In this work, we have adopted the SUMO fusion technology for the expression of triabin in E. coli cells-with facile refolding and purification procedures-and the bioactive triabin was produced in ∼12 mg/L culture medium. Subsequently, the structure-function studies through extensive site-directed mutagenesis reveal that triabin's Phe-106 involved in the hydrophobic contacts plays a surprisingly important role in the thrombin inhibition, in contrast to the negatively charged residues Asp-135 or Glu-128 involved in the salt-bridge interaction. As such, this study complements our understanding of the interaction mechanism of natural thrombin inhibitors, which should facilitate the development of anticoagulant drugs with a novel mode of action against thrombin.

Heterologous expression of novel SUMO proteases from Schizosaccharomyces pombe in E. coli: Catalytic domain identification and optimization of product yields

Small ubiquitin-related modifier (SUMO) proteins are efficiently used to target the soluble expression of various difficult-to-express proteins in E. coli. However, its utilization in large scale protein production is restricted by the higher cost of Ulp, which is required to cleave SUMO fusion tag from protein-of-interest to generate an authentic N-terminus. This study identified and characterized two novel SUMO proteases i.e., Ulp1 and Ulp2 from Schizosaccharomyces pombe. Codon-optimized gene sequences were cloned and expressed in E. coli. The sequence and structure of SpUlp1 and SpUlp2 catalytic domains were deduced using bioinformatics tools. Protein-protein interaction studies predicted the higher affinity of SpUlp1 towards SUMO compared to its counterpart from Saccharomyces cerevisiae (ScUlp1). The catalytic domain of SpUlp1 was purified using Ni-NTA chromatography with 83.33% recovery yield. Moreover, In vitro activity data further confirmed the fast-acting nature of SpUlp1 catalytic domain, where a 90% cleavage of fusion proteins was obtained within 1 h of incubation, indicating novelty and commercial relevance of S. pombe Ulp1. Biophysical characterization showed 8.8% α-helices, 36.7% β-sheets in SpUlp1SD. From thermal CD and fluorescence data, SpUlp1SD T_m was found to be 45 °C. Further, bioprocess optimization using fed-batch cultivation resulted in 3.5 g/L of SpUlp1SD production with Y_P/X of 77.26 mg/g DCW and volumetric productivity of 205.88 mg/L/h.

A vaccine using Anaplasma marginale subdominant type IV secretion system recombinant proteins was not protective against a virulent challenge

Anaplasma marginale is the most prevalent tick-borne livestock pathogen with worldwide distribution. Bovine anaplasmosis is a significant threat to cattle industry. Anaplasmosis outbreaks in endemic areas are prevented via vaccination with live A. centrale produced in splenectomized calves. Since A. centrale live vaccine can carry other pathogens and cause disease in adult cattle, research efforts are directed to develop safe recombinant subunit vaccines. Previous work found that the subdominant proteins of A. marginale type IV secretion system (T4SS) and the subdominant elongation factor-Tu (Ef-Tu) were involved in the protective immunity against the experimental challenge in cattle immunized with the A. marginale outer membrane (OM). This study evaluated the immunogenicity and protection conferred by recombinant VirB9.1, VirB9.2, VirB10, VirB11, and Ef-Tu proteins cloned and expressed in E. coli. Twenty steers were randomly clustered into four groups (G) of five animals each. Cattle from G1 and G2 were immunized with a mixture of 50 μg of each recombinant protein with Quil A® or Montanide™ adjuvants, respectively. Cattle from G3 and G4 (controls) were immunized with Quil A and Montanide adjuvants, respectively. Cattle received four immunizations at three-week intervals and were challenged with 107 A. marginale-parasitized erythrocytes 42 days after the fourth immunization. After challenge, all cattle showed clinical signs, with a significant drop of packed cell volume and a significant increase of parasitized erythrocytes (p<0.05), requiring treatment with oxytetracycline to prevent death. The levels of IgG2 induced in the immunized groups did not correlate with the observed lack of protection. Additional strategies are required to evaluate the role of these proteins and their potential utility in the development of effective vaccines.

Chenodeoxycholic Acid Modulates Bile Acid Synthesis Independent of Fibroblast Growth Factor 19 in Primary Human Hepatocytes

Bile acids (BAs) are detergents essential for intestinal absorption of lipids. Disruption of BA homeostasis can lead to severe liver damage. BA metabolism is therefore under strict regulation by sophisticated feedback mechanisms. The hormone-like protein Fibroblast growth factor 19 (FGF19) is essential for maintaining BA homeostasis by down regulating BA synthesis. Here, the impact of both FGF19 and chenodeoxycholic acid (CDCA) on primary human hepatocytes was investigated and a possible autocrine/paracrine function of FGF19 in regulation of BA synthesis evaluated. Primary human hepatocytes were treated with CDCA, recombinant FGF19 or conditioned medium containing endogenously produced FGF19. RNA sequencing revealed that treatment with CDCA causes deregulation of transcripts involved in BA metabolism, whereas treatment with FGF19 had minor effects. CDCA increased FGF19 mRNA expression within 1 h. We detected secretion of the resulting FGF19 protein into medium, mimicking in vivo observations. Furthermore, medium enriched with endogenously produced FGF19 reduced BA synthesis by down regulating CYP7A1 gene expression. However, following knockdown of FGF19, CDCA still independently decreased BA synthesis, presumably through the regulatory protein small heterodimer partner (SHP). In summary, we show that in primary human hepatocytes CDCA regulates BA synthesis in an FGF19-independent manner.

Bioprocess optimization for the overproduction of catalytic domain of ubiquitin-like protease 1 (Ulp1) from S. cerevisiae in E. coli fed-batch culture

The exploitation of SUMO (small ubiquitin-related modifier) fusion technology at a large scale for the production of therapeutic proteins with an authentic N-terminus is majorly limited due to the higher cost of ScUlp1 protease. Therefore, the cost-effective production of Saccharomyces cerevisiae Ulp1 protease catalytic domain (402-621 aa) was targeted via its cloning under strong T7 promoter with and without histidine tag. The optimization of cultivation conditions at shake flask resulted in ScUlp1 expression of 195 mg/L in TB medium with a specific product yield of 98 mg/g DCW. The leaky expression of the ScUlp1 protease was controlled using the chemically defined minimal medium. The Ni-NTA affinity purification of ScUlp1 was done near homogeneity using different additives (0.1% Triton X-100, 0.01 mM DTT, 0.02 mM EDTA and 1% glycerol) where a product purity of ∼95% with a recovery yield of 80% was obtained. The specific activity of purified ScUlp1 was found to be 3.986 × 10⁵ U/mg. The ScUlp1 protease successfully cleaved the SUMO tag even at 1:10,000 enzyme to substrate ratio with high efficacy and also showed a comparable catalytic efficiency as of commercial control. Moreover, the in vivo cleavage of SUMO tag via co-expression strategy also resulted in more than 80% cleavage of SUMO fusion protein. The optimization of high cell density cultivation strategies and maintenance of higher plasmid stability at bioreactor level resulted in the ScUlp1 production of 3.25 g/L with a specific product yield of 45.41 mg/g DCW when cells were induced at an OD₆₀₀ of 132 (63.66 g/L DCW).

Fibroblast Growth Factor 15-Dependent and Bile Acid-Independent Promotion of Liver Regeneration in Mice

The role of intestine-derived factors in promoting liver regeneration after partial hepatectomy (PHx) are not entirely known, but bile acids (BAs) and fibroblast growth factor 15 (Fgf15) that is highly expressed in the mouse ileum could promote hepatocyte proliferation. Fgf15 strongly suppresses the synthesis of BAs, and emerging evidence indicates that Fgf15 is important for liver regeneration. The mechanisms by which Fgf15 promotes liver regeneration are unclear, but Fgf15 may do so indirectly by reducing BA levels and/or directly by promoting cell proliferation. However, it remains undetermined whether these two mechanisms are independent or integrated. In this study, we aimed to clarify these relationships by generating Fgf15 Tet-Off, transgenic mice (Fgf15 Tg) that had very low BA levels as a result from overexpressed Fgf15-mediated suppression of BA synthesis. Compared with wild-type mice, the Fgf15 Tg mice showed increased hepatocyte proliferation even without surgery, and a further induction of the genes in cell-cycle progression after PHx. Moreover, overexpression of Fgf15 by adeno-associated virus (AAV)-Fgf15 transduction or treatment with the recombinant Fgf15 protein led to increased cell proliferation in vivo. Furthermore, Fgf15 Tg mice exhibited an earlier and greater activation of mitogen-activated protein kinase, signal transducer and activator of transcription 3, and NF-κB signaling pathways in the priming stage, and a disruption of the hippo signaling pathway in the termination stage of liver regeneration. Conclusion: Direct in vivo evidence demonstrates that Fgf15 is critical in stimulating the phases of priming and termination of liver regeneration that are critical for cell survival and liver-size determination, independent of BA levels. (Hepatology 2018; 00:000-000).

Small Ubiquitin-Like Modifier Protein 3 Enhances the Solubilization of Human Bone Morphogenetic Protein 2 in E. coli

Small ubiquitin-like modifier (SUMO) fusion technology is widely used in the production of heterologous proteins from prokaryotic system to aid in protein solubilization and refolding. Due to an extensive clinical application of human bone morphogenetic protein 2 (hBMP2) in bone augmentation, total RNA was isolated from human gingival tissue and mature gene was amplified through RT-PCR, cloned (pET21a), sequence analyzed, and submitted to GenBank (Accession no. KF250425). To obtain soluble expression, SUMO3 was tagged at the N-terminus of hBMP2 gene (pET21a/SUMO3-hBMP2), transferred in BL21 codon+, and ~ 40% soluble expression was obtained on induction with IPTG. The dimerized hBMP2 was confirmed with Western blot, native PAGE analysis, and purified by fast protein liquid chromatography with 0.5 M NaCl elution. The cleavage of SUMO3 tag from hBMP2 converted it to an insoluble form. Computational 3D structural analysis of the SUMO3-hBMP2 was performed and optimized by molecular dynamic simulation. Protein-protein interaction of SUMO3-hBMP2 with BMP2 receptor was carried out using HADDOCK and inferred stable interaction. The alkaline phosphatase assay of SUMO3-hBMP2 on C2C12 cells showed maximum 200-ng/ml dose-dependent activity. We conclude that SUMO3-tagged hBMP2 is more suited for generation of soluble form of the protein and addition of SUMO3 tag does not affect the functional activity of hBMP2.

Cell-penetrating and endoplasmic reticulum-locating TAT-IL-24-KDEL fusion protein induces tumor apoptosis

Interleukin-24 (IL-24) is a unique IL-10 family cytokine that could selectively induce apoptosis in cancer cells without harming normal cells. Previous research demonstrated that intracellular IL-24 protein induces an endoplasmic reticulum (ER) stress response only in cancer cells, culminating in apoptosis. In this study, we developed a novel recombinant fusion protein to penetrate into cancer cells and locate on ER. It is composed of three distinct functional domains, IL-24, and the targeting domain of transactivator of transcription (TAT) and an ER retention four-peptide sequence KDEL (Lys-Asp-Glu-Leu) that link at its NH2 and COOH terminal, respectively. The in vitro results indicated that TAT-IL-24-KDEL inhibited growth in bladder cancer cells, as well as in non-small cell lung cancer cell line and breast cancer cell line, but the normal human lung fibroblast cell line was not affected, indicating the cancer specificity of TAT-IL-24-KDEL. Western blot analysis showed that apoptosis activation was induced by TAT-IL-24-KDEL through the ER stress-mediated cell death pathway. Treatment with TAT-IL-24-KDEL significantly inhibited the growth of human H460 xenografts in nude mice, and the tumor growth inhibition was correlated with increased hematoxylin and eosin (H&E) staining and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining. These findings suggest that the artificially designed recombinant fusion protein TAT-IL-24-KDEL may be highly effective in cancer therapy and worthy of further evaluation and development.

Expression of soluble and active interferon consensus in SUMO fusion expression system in E. coli

Protein production can be improved if methods for soluble protein expression are developed. Interferon consensus (IFN-con) is used to treat hepatitis C. IFN-con has superior activity compared to other clinically used interferon α subtypes. However IFN-con is a challenging protein to produce in a soluble form using an Escherichia coli expression system. Here we describe the expression of soluble and active recombinant IFN-con in E. coli. The IFN-con gene sequence was optimised for expression in E. coli, which was then cloned into the Champion™ pET SUMO expression vector downstream of the SUMO fusion protein and under strong T7lac promoter. The SUMO-IFN-con fusion protein was efficiently expressed using the SHuffle™ E. coli strain and existed in soluble form as 86-88% of the total IFN-con. After removal of the SUMO fusion partner, approximately 50mg of recombinant IFN-con of at least 98% purity (by RP-HPLC) was obtained from a 1L fermentation culture. Using an A549/EMCV antiviral assay, the specific activity of the recombinant IFN-con was determined to be 960×10(6) IU/mg as calculated to NIBSC standard for IFN-con (3×10(5)pfu/mL virus titre). Comparison of the antiviral activity of the produced IFN-con to IFN α-2a showed that IFN-con displays 2.8 times greater activity, which is in good agreement with what has been reported in the literature for pure protein. IFN-con expression in a soluble form from E. coli allowed us to use a simple, two-step purification process to yield highly pure and active IFN-con which is more efficient than obtaining IFN-con from inclusion bodies.

Soluble expression of disulfide bond containing proteins FGF15 and FGF19 in the cytoplasm of Escherichia coli

Fibroblast growth factor 19 (FGF19) is the human ortholog of mouse FGF15, and both proteins function as an endocrine signal to regulate various liver functions. FGF15/FGF19 protein contains two disulfide bonds. It is unfavorable to form disulfide bonds in Escherichia coli (E. coli) cytoplasm because of the bacterial cytoplasmic reducing environment. Modification of the cytoplasmic reducing environment and/or co-expression of protein chaperones are common strategies to express disulfide bond containing proteins in E. coli. In the current study, we report a method to produce soluble FGF15/FGF19 protein in cytoplasm of E. coli. Several commercial available strains with the disruption of thiol-redox pathways, and/or co-expression of redoxase or refolding chaperones were used to develop this novel method for expression of FGF15/FGF19 in E. coli. Mutation of the thiol-disulfide bond reducing pathway in E. coli or N-terminal fusion of thioredox (TRX) alone is not enough to support disulfide bond formation in FGF15/19 proteins. However, TRX fusion protein improved FGF19 solubility in strains of thiol-redox system mutants. In addition, DsbC co-expressed in thiol-redox system mutants alone improved and further enhanced FGF19 solubility with combination of TRX fusion tag. The soluble FGF19 proteins were easily purified through Ni-NTA affinity chromatography and anion exchange chromatography, and the purified protein maintained its biological activities, confirmed by suppressing hepatic Cyp7a1 gene transcription in mice and by activating ERK1/2 signaling pathway in HepG2 cells. In contrast, soluble FGF15 protein in cytoplasm remained very low using these strategies. In summary, we have successfully developed a method to express functional FGF19 protein in prokaryotic cells, and this strategy may be adapted for the expression of other disulfide-containing proteins.

A His6-SUMO-eXact tag for producing human prepro-urocortin 2 in Escherichia coli for raising monoclonal antibodies

This is a first report of recombinant production of human prepro-Urocortin 2 in Escherichia coli by N-terminal fusion with a triple His₆-SUMO-eXact tag and its subsequent use as an antigen for the production and screening of very high affinity monoclonal antibodies. The rationale for this combinatorial construct is that the His tag allows first step protein purification of insoluble and soluble proteins, the SUMO tag enhances protein expression level and solubility, while the eXact tag facilitates anion-triggered on-column cleavage of the triple tag to recover pure native proteins in a simple two-step protein purification procedure. Compared with an eXact fusion alone, the presence of the SUMO moiety enhanced overall expression levels by 4 to 10 fold but not the solubility of the highly basic prepro-Urocortin 2. Insoluble SUMO-eXact-preproUCN2 was purified in milligram quantities by denaturing IMAC and solubilized in native phosphate buffer by on-column refolding or step-wise dialysis. Only a small fraction of this solubilized protein was able to bind onto the eXact™ affinity column and cleaved by NaF treatment. To test whether binding and cleavage failure was due to improperly refolded SUMO-eXact-preproUCN2 or to the presence of N- and C-terminal sequences flanking the eXact moiety, we created a SUMO-eXact-thioredoxin construct which was overexpressed mainly in the soluble form. This protein bound to and was cleaved efficiently on the eXact™ column to yield native thioredoxin. Solubilized SUMO-eXact-preproUCN2 was used successfully to generate two high affinity mouse monoclonal antibodies (KD~10⁻¹⁰ and 10⁻¹¹ M) specific to the pro-region of Urocortin 2.

Mechanism of tissue-specific farnesoid X receptor in suppressing the expression of genes in bile-acid synthesis in mice

Activation of farnesoid X receptor (Fxr, Nr1h4) is a major mechanism in suppressing bile-acid synthesis by reducing the expression levels of genes encoding key bile-acid synthetic enzymes (e.g., cytochrome P450 [CYP]7A1/Cyp7a1 and CYP8B1/Cyp8b1). FXR-mediated induction of hepatic small heterodimer partner (SHP/Shp, Nr0b2) and intestinal fibroblast growth factor 15 (Fgf15; FGF19 in humans) has been shown to be responsible for this suppression. However, the exact contribution of Shp/Fgf15 to this suppression, and the associated cell-signaling pathway, is unclear. By using novel genetically modified mice, the current study showed that the intestinal Fxr/Fgf15 pathway was critical for suppressing both Cyp7a1 and Cyp8b1 gene expression, but the liver Fxr/Shp pathway was important for suppressing Cyp8b1 gene expression and had a minor role in suppressing Cyp7a1 gene expression. Furthermore, in vivo administration of Fgf15 protein to mice led to a strong activation of extracellular signal-related kinase (ERK) and, to a smaller degree, Jun N-terminal kinase (JNK) in the liver. In addition, deficiency of either the ERK or JNK pathway in mouse livers reduced the basal, but not the Fgf15-mediated, suppression of Cyp7a1 and Cyp8b1 gene expression. However, deficiency of both ERK and JNK pathways prevented Fgf15-mediated suppression of Cyp7a1 and Cyp8b1 gene expression.

CONCLUSION

The current study clearly elucidates the underlying molecular mechanism of hepatic versus intestinal Fxr in regulating the expression of genes critical for bile-acid synthesis and hydrophobicity in the liver.

Post-production protein stability: trouble beyond the cell factory

Being protein function a conformation-dependent issue, avoiding aggregation during production is a major challenge in biotechnological processes, what is often successfully addressed by convenient upstream, midstream or downstream approaches. Even when obtained in soluble forms, proteins tend to aggregate, especially if stored and manipulated at high concentrations, as is the case of protein drugs for human therapy. Post-production protein aggregation is then a major concern in the pharmaceutical industry, as protein stability, pharmacokinetics, bioavailability, immunogenicity and side effects are largely dependent on the extent of aggregates formation. Apart from acting at the formulation level, the recombinant nature of protein drugs allows intervening at upstream stages through protein engineering, to produce analogue protein versions with higher stability and enhanced therapeutic values.