Vasily N. Stepanenko

Production of recombinant human epidermal growth factor using Ssp dnaB mini-intein system

Chemical-enzymatic synthesis of human Epidermal Growth Factor (hEGF) cDNA has been performed, following by cloning into expression vector pTWIN1 (New England Biolabs). The resulting recombinant fusion protein expressed in Escherichia coli consisted of the N-terminal chitin-binding domain, mini-intein Ssp dnaB domain and hEGF polypeptide at the C-terminus. In this construct, mini-intein Ssp dnaB played a role of catalytically active subunit capable under certain conditions of autocatalytic cleavage resulting in separation of the target protein. As the hybrid protein had several cysteins in its sequence-one in chitin-binding domain, one in mini-intein and six in hEGF, it was necessary to work out optimal scheme for refolding and purification of the recombinant hEGF. As a result of this work, two schemes of the recombinant hEGF purification have been developed: according to the first scheme, the recombinant protein with reduced cysteins is bound to the chitin column, the hEGF is cleaved off and eluted, and then refolded to form appropriate cystein bridges. In the second scheme, the entire hybrid protein is first refolded to form disulfide bonds and then loaded to affinity resin; the recombinant hEGF is cleaved off and eluted in its native state. In spite of the fact that the first scheme is more common and suitable for a variety of recombinant proteins, in case of recombinant hEGF, the second scheme proved to be more productive and cost-effective.

Production and Purification of Recombinant Human Glucagon Overexpressed as Intein Fusion Protein in Escherichia coli

Chemico-enzymatic synthesis and cloning in Esherichia coli of an artificial gene coding human glucagon was performed. Recombinant plasmid containing hybrid glucagons gene and intein Ssp dnaB from Synechocestis sp. was designed. Expression of the obtained hybrid gene in E. coli, properties of the formed hybrid protein, and conditions of its autocatalytic cleavage leading to glucagon formation were studied.

Production of thymosin α1 via non-enzymatic acetylation of the recombinant precursor

Human thymosin α1 is an effective immune system enhancer for the treatment of cancer and viral diseases. Therefore the development of new methods for its synthesis is an urgent problem. In the present work, we propose an efficient scalable scheme for the production of recombinant thymosin α1. We used an expression system based on the pET32b+ plasmid and Escherichia coli strain ER2566 to obtain a fusion protein consisting of thymosin α1 and thioredoxin separated by a TEV (tobacco etch virus) protease cleavage site. The fusion protein was overexpressed in soluble form and purified by ion‐exchange chromatography. After proteolytic cleavage of the fusion protein with TEV protease, recombinant desacetylthymosin α1 was isolated by ultrafiltration. Acetic anhydride was used for selective N‐terminal acetylation of the obtained peptide (yield=62%). The resultant thymosin α1 was purified by RP‐HPLC (reversed‐phase HPLC). The distinctive feature of this technology is that it is a combination of different approaches: the biotechnological production of recombinant fusion protein, its enzymatic cleavage, and chemical acetylation of desacetylthymosin α1. Each stage of the process was optimized to increase the yield of the target peptide, which averaged 29 mg/litre of bacterial culture. The proposed method is simple and cost‐effective and is suitable for large‐scale production of recombinant thymosin α1.

Development of the intein-mediated method for production of recombinant thymosin β4 from the acetylated in vivo fusion protein.

Thymosin β4 is a 43 amino acid long peptide with an acetylated N-terminal serin that has a high potential as a remedy for healing ulcers, wounds and burns. Although protein biosynthesis offers attractive opportunities in terms of a large-scale production, currently thymosin β4 is mainly produced by chemical synthesis. The problems that hinder the successful commercialization of the biotechnological approach are associated with the small peptides expression and N-terminal acetylation. This work presents an innovative biotechnological method for thymosin β4 production that employs the peptide acetylation in vivo. A genetically engineered construct was created, where the Tβ4 coding sequence fused with the intein Mxe GyrA sequence and chitin-binding domain was combined with the acetyltransferase coding sequence to form a polycistronic construct under a stringent control of T7 promoter. This plasmid construct provided for the expression of the Tβ4-intein fusion protein. In the process of the post-translational modification in vivo formyl methionine was completely removed from the target peptide N-terminus and followed by the Tβ4 precursor N-terminal acetylation. The use of the intein-mediated expression system made it possible to extract thymosin β4 in only 2 chromatographic runs. The method is straightforward to implement and scale up.

Recombinant Thymosin α1

An artificial gene encoding thymosin α1 was obtained by chemoenzymatic synthesis and cloned into Escherichia coli. An expressing recombinant plasmid containing the hybrid protein gene, which encodes amino acid sequences of thymosin α1 and the Saccharomycescerevisiae intein Sce VMA, was constructed. The expression of the hybrid protein from the resulting hybrid gene in E. coli, the properties of the resulting hybrid protein, and the conditions for its nonenzymatic cleavage to thymosin α1 were studied.

Production of Recombinant Oxytocin Through Sulfitolysis of Inteincontaining Fusion Protein

An artificial gene consisting of seven copies of an oxytocinoyl-lysine encoding sequence arranged in a tandem was synthesized and inserted downstream of the SspDnaB intein gene in a pTWIN1 plasmid. The corresponding fusion protein Dnab-7oxy contained 16 cysteine residues and formed inclusion bodies when expressed in E. coli. The standard protocol involving solubilization of the fusion protein and its autocatalytic cleavage on a chitin resin was not effective because of a very low yield of the cleavage reaction. Attempts to perform a refolding of the intein part of the fusion protein in solution were also unsuccessful because of a high level of protein aggregation. Sulfitolysis of cysteine residues is known to increase a solubility of proteins and peptides. Therefore we suggested a one-step approach that combines solubilization of inclusion bodies and sulfitolysis of a hybrid protein. The fusion protein was completely reduced and solubilized in 8M urea at pH 9.0 in the presence of sodium sulfite and sodium tetrathionate. The sulfitized protein was loaded onto a chitin column, an efficient cleavage was induced by a pH shift from 9.0 to 6.5, and seven successively connected oxytocinoyl- lysine units were released. The heptamer was subjected to trypsinolysis yielding sulfitized monomers of oxytocinoyllysine. Oxytocinoyl-lysine was refolded as described previously and treated by carboxypeptidase B to form the oxytocinic acid. The target oxytocin amide was then synthesized via methyl ester intermediate. Using this approach 6 mg of recombinant oxytocin can be obtained from 1 g of biomass.

Antiangiogenic and antivascular effects of a recombinant tumstatin-derived peptide in a corneal neovascularization model

Tumstatin, a cleavage fragment of collagen IV, is a potent endogenous inhibitor of angiogenesis. Tumstatin-derived peptide T8 possesses all angiostatic properties of full-length tumstatin and indirectly suppresses tumor growth. The potential of T8 to block pathological angiogenesis in the eye has not been explored yet. Here we assess antiangiogenic effects of a recombinant T8 peptide in rabbit corneal neovascularization models. The fusion protein consisting of T8 and thioredoxin was synthesized in a highly efficient Escherichia coli expression system, isolated using ion-exchange chromatography and cleaved with TEV (tobacco etch virus) protease. The target peptide was purified on an anion-exchange resin and by reversed phase high-performance liquid chromatography. The recombinant peptide suppressed the proliferation of basic fibroblast growth factor-induced SVEC-4-10 endothelial cells (simian virus 40-immortalized murine endothelial cells) and inhibited tube formation in these cells in a dose-dependent manner. In rabbit corneal neovascularization models T8 demonstrated the ability to prevent pathological angiogenesis (when injected simultaneously with the induction of neovascularization) and, moreover, to promote the regression of newly-formed blood vessels (when injected on day 8 after angiogenesis stimulation). Our results suggest that T8 may have a therapeutic potential in the treatment of ocular neovascular diseases.

Biotechnological production of acetylated thymosin β4

Thymosin β4 (43 aa) is a highly conserved acidic peptide, which regulates actin polymerization in mammalian cells by sequestering globular actin. Thymosin β4 is undergoing clinical trials as a drug for treatment of venous stasis ulcers, corneal wounds and injuries, as well as acute myocardial infarction. Currently, thymosin β4 is produced by a solid-phase chemical synthesis. Biotechnological synthesis of this peptide is difficult, because the N-terminal amino acid residue of thymosin β4 playing an essential role in the actin interaction is acetylated. In this study, we proposed a method for production of a thymosin β4 recombinant precursor and its directed chemical acetylation. Deacetylthymosin β4 was synthesized as a part of a hybrid protein containing thioredoxin and a specific TEV (tobacco etch virus) protease cleavage site. The following scheme was developed for purification of deacetylthymosin β4: (i) biosynthesis of a soluble hybrid protein (HP) in Escherichia coli, (ii) isolation of HP by ion exchange chromatography, (iii) cleavage of HP with TEV protease, and (iv) purification of deacetylthymosin β4 by ultrafiltration. N-Terminal acetylation of the serine residue of deacetylthymosin β4 was performed with acetic anhydride under acidic conditions (pH 3.0). The reaction yield was 55%. Thymosin β4 was finally purified by reverse-phase HPLC. The proposed method of isolation of recombinant thymosin β4 can be scaled-up and provide a highly purified preparation in a yield of 20 mg per 1 L of culture suitable for use in medical practice.

Cloning, expression, isolation, and properties of thymidine kinase from herpes simplex virus type 1, strain L2

Thymidine kinase UL23 gene (EC 2.7.1.145) from the L2 acyclovir-sensitive strain of herpes simplex virus type 1 was cloned and expressed in E. coli. The enzyme was purified by chromatography to the purity of 90% according to PAG electrophoresis data. The Michaelis constants for the reactions with thymidine and acyclovir were determined. The enzyme was found to phosphorylate modified nucleosides, particularly 3′-deoxythymidine, 3′-deoxy-2′,3′-didehydrothymidine, 2′,3′-dideoxycytidine, 9-[(hydroxyethyl)methyl]guanine, E-5-(2-bromovinyl-2′-deoxyuridine, 9-(1,3-dihydroxy-2-propoxymethyl)guanine, 2′,3′-dideoxydehydrothymidine, β-L-2′,3′-dideoxy-3′-thiacytidine, and 3′-fluoro-3′-deoxythymidine. Some properties of the purified enzyme were compared with those of thymidine kinases of other herpes simplex virus strains. It was shown that acyclovir H-phosphonate inhibited the enzyme.

Pilot production of the recombinant peptide toxin of Heteractis crispa as a potential analgesic by intein-mediated technology

APHC3 is an analgesic polypeptide that was found in the sea anemone (Heteractis crispa), and contains 56 amino acid residues. This polypeptide is of interest for the development of medications for diseases, associated with inflammatory or neuropathological processes, as well as its use as an analgesic. This work presents an innovative biotechnological method for APHC3 production. We have constructed a recombinant plasmid intended for biosynthesizing the fusion protein consisting of a chitin-binding domain, DnaB mini-intein from Synechocystis sp. capable of undergoing pH-dependent self-cleavage, and the target peptide. In the process of biosynthesis the fusion protein aggregates and forms the inclusion bodies that are welcomed since APHC3 is a cytotoxic peptide. The target peptide recovery process developed by us involves 3 chromatographic steps. The method developed by us enables to produce 940 mg of the recombinant APHC3 from 100 g of the inclusion bodies. The method is straightforward to implement and scale up. The recombinant APHC3 activity and effectiveness as an analgesic was proved by animal testing.