Expression and purification of lacticin Q by small ubiquitin-related modifier fusion in <Emphasis Type="Italic">Escherichia coli</Emphasis>

Lacticin Q is a broad-spectrum class II bacteriocin with potential as an alternative to conventional antibiotics. The objective of this study was to produce recombinant lacticin Q using a small ubiquitin-related modifier (SUMO) fusion protein expression system. The 168-bp lacticin Q gene was cloned into the expression vector pET SUMO and transformed into Escherichia coli BL21(DE3). The soluble fusion protein was recovered with a Ni-NTA Sepharose column (95% purity); 130 mg protein was obtained per liter of fermentation culture. The SUMO tag was then proteolytically cleaved from the protein, which was re-applied to the column. Finally, about 32 mg lacticin Q (≥96% purity) was obtained. The recombinant protein exhibited antimicrobial properties similar to that of the native protein, demonstrating that lacticin Q had been successfully expressed by the SUMO fusion system.     

Production of glutamine synthetase in <Emphasis Type="Italic">Escherichia coli</Emphasis> using SUMO fusion partner and application to <Emphasis Type="SmallCaps">l</Emphasis>-glutamine synthesis

l-glutamine (Gln) is an important conditionally necessary amino acid in human body and potential demand in food or medicine industry is expected. High efficiency of l-Gln production by coupling genetic engineered bacterial glutamine synthetase (GS) with yeast alcoholic fermentation system has been developed. We report here first the application of small ubiquitin-related modifier (SUMO) fusion technology to the expression and purification of recombinant Bacillus subtilis GS. In order to obtain GS with high Gln-forming activity, safety and low cost for food and pharmaceutics industry, 0.1% (w/v) lactose was selected as inducer. The fusion protein was expressed in totally soluble form in E. coli, and expression was verified by SDS–PAGE and western blot analysis. The fusion protein was purified to 90% purity by nickel nitrilo-triacetic acid (Ni–NTA) resin chromatography with a yield of 625 mg per liter fermentation culture. After the SUMO/GS fusion protein was cleaved by the SUMO protease, the cleaved sample was reapplied to a Ni–NTA column. Finally, about 121 mg recombinant GS was obtained from 1 l fermentation culture with no less than 96% purity. The recombinant purified GS showed great transferase activity (23 U/mg), with 25 U recombinant GS in a 50 ml reaction system, a biosynthesis yield of 27.5 g/l l-Gln was detected by high pressure liquid chromatography (HPLC) or thin-layer chromatography. Thus, the application of SUMO technology to the expression and purification of GS potentially could be employed for the industrial production of l-Gln.     

Production of Bioactive Human Beta-Defensin-4 in <Emphasis Type="Italic">Escherichia coli</Emphasis> Using SUMO Fusion Partner

The human beta defensins-4 (hBD4) exhibit a broad range of antimicrobial properties and are thought to be ideal therapeutic agents because of their potential ability to circumvent the problems of acquired resistance often observed with other antimicrobial therapies. We report here the application of small ubiquitin-related modifier (SUMO) fusion technology to the expression and purification of cationic antibacterial peptide hBD4. The fusion protein expressed in a soluble form was purified to a purity of 90% by Ni-IDA chromatography and 637 mg protein of interest was obtained per liter of fermentation culture. After the SUMO-hBD4 fusion protein was cleaved by the SUMO protease at 30 °C for 1 h, the cleaved sample was re-applied to a Ni-IDA. Finally, about 166 mg recombinant hBD4 was obtained from 1 L fermentation culture with no less than 96% purity and the recombinant hBD4 had similar antimicrobial properties to the synthetic hBD4. Thus, the SUMO-mediated peptide expression and purification system potentially could be employed for the production of recombinant cytotoxic peptides.     

Biodiversity in aerobic granule membrane bioreactor at high organic loading rates

Antibacterial peptide CM4 (ABP-CM4) is a small cationic peptide with broad-spectrum activities against bacteria, fungi, and tumor cells, which may possibly be used as an antimicrobial agent. We report here the application of small ubiquitin-related modifier (SUMO) fusion technology to the expression and purification of cationic antibacterial peptide ABP-CM4. The fusion protein expressed in a soluble form was purified to a purity of 90% by Ni-IDA chromatography and 112 mg protein of interest was obtained per liter of fermentation culture. After the SUMO–CM4 fusion protein was cleaved by the SUMO protease at 30 °C for 1 h, the cleaved sample was re-applied to a Ni-IDA. Finally, about 24 mg recombinant CM4 was obtained from 1 l fermentation culture with no less than 96% purity and the recombinant CM4 had similar antimicrobial properties to the synthetic CM4. Thus, the SUMO-mediated peptide expression and purification system potentially could be employed for the production of recombinant cytotoxic peptides.     

SUMO蛋白酶的发酵和纯化工艺的研究

目前, 小分子肽多需要进行融合表达,虽然有GST标签等表达体系,但是表达产物切割时仍留有多余氨基酸,影响小分子肽的功能;SUMO蛋白酶对SUMO融合表达系统表达的重组蛋白进行切割时没有多余氨基酸残留,因此成为蛋白切割工具的热点。利用基因工程技术构建重组His-Ulp1/pET3c/BL21（DE3）工程菌株,用摇瓶优化表达条件,摸索高密度发酵工艺和不同层析纯化工艺条件。结果表明,经1.0mmol/L的IPTG 30℃诱导表达6h,表达效果最好。罐发酵后菌体SDSPAGE分析表达量可达24.39%,通过CM Sepharose Fast Flow阳离子交换一步层析可获得纯度大于98%的SUMO蛋白酶,每升发酵液可获得355mg的SUMO蛋白酶纯品。Western blot分析表明,UlP1能与6×His抗体产生免疫反应。为日后大规模产业化生产奠定了基础。     

Expression and Purification of Human Keratinocyte Growth Factor 2 by Fusion with SUMO

Small ubiquitin-related modifier (SUMO) fusion system has been shown to be efficient for enhancing expression and preventing degradation of the target protein. We showed herein that SUMO fusion to human keratinocyte growth factor 2 (hKGF-2) gene was feasible and it significantly enhanced protein expression and its efficiency. The fusion DNA fragment composed of SUMO gene, which was fused to hexahistidine tag, and hKGF-2 gene was amplified by PCR and inserted into the expression vector pET28a to construct the recombinant plasmid, pET28a-SUMO-hKGF-2. The plasmid was then transformed into Escherichia coli Rosetta^TM2(DE3), and the recombinant fusion protein SUMO-hKGF-2 was expressed at 30°C for 6 h, with the induction of IPTG at the final concentration of 0.4 mM. The expression level of the fusion protein was up to 30% of the total cellular protein. The fusion protein was purified by Ni-NTA affinity chromatography. After desalting by Sephadex G-25 size exclusion chromatography, the hexahistidine-SUMO-hKGF-2 was digested by SUMO proteases. The recombinant hKGF-2 was purified again with Ni-NTA column and the purity was about 95% with a total yield of 13.9 mg/l culture. The result of mitogenicity assay suggests that the recombinant hKGF-2 can significantly promote the proliferation of normal rat kidney epithelial (NRK-52E) cells. Xiaoping Wu, and Changjun Nie contributed equally to the work.     

Production of Bioactive γ-Glutamyl Transpeptidase in <Emphasis Type="Italic">Escherichia coli</Emphasis> Using SUMO Fusion Partner and Application of the Recombinant Enzyme to <Emphasis Type="SmallCaps">l</Emphasis>-Theanine Synthesis

The amino acid l-theanine (γ-glutamylethylamide) has potential important applications in the food and pharmaceutical industries and increased demand for this compound is expected. It is the major “umami” (good taste) component of tea and its favorable physiological effects on mammals have been reported. An enzymatic method for the synthesis of l-theanine involving recombinant Escherichia coli γ-glutamyltranspeptidase (GGT) has been developed. We report here the application of small ubiquitin-related modifier (SUMO) fusion technology to the expression and purification of recombinant Escherichia coli γ-GGT. In order to obtain γ-GGT with high theanine-forming activity, safety, and low cost for food and pharmaceutics industry, M9 (consisting of glycerol and inorganic salts) and 0.1% (w/v) lactose were selected as culture medium and inducer, respectively. The fusion protein was expressed in soluble form in E. coli, and expression was verified by SDS-PAGE and western blot analysis. The fusion protein was purified to 90% purity by nickel–nitrilotriacetic acid (Ni–NTA) resin chromatography with a yield of 115 mg per liter fermentation culture. After the SUMO/γ-GGT fusion protein was cleaved by the SUMO protease, the cleaved sample was reapplied to a Ni–NTA column. Finally, about 62 mg recombinant γ-GGT was obtained from 1 l fermentation culture with no less than 95% purity. The recombinant γ-GGT showed great transpeptidase activity, with 1500 U of purified recombinant γ-GGT in a 1-l reaction system, a biosynthesis yield of 41 g of l-theanine was detected by paper chromatography or high pressure liquid chromatography (HPLC). Thus, the application of SUMO technology to the expression and purification of γ-GGT potentially could be employed for the industrial production of l-theanine.     

Expression and purification of soluble B lymphocyte stimulator from recombinant <Emphasis Type="Italic">Escherichia coli</Emphasis>

In this work, the expression conditions of fusion protein thioredoxin (Trx)-soluble B lymphocyte stimulator (sBLyS) in a shake flask and bioreactor from the recombinant Escherichia coli BL21 (DE3) with a pET system encoding the fusion protein gene of Trx-sBLyS and the purification method of the sBLyS were optimized to effectively obtain the bioactive protein sBLyS with a high purity. A yield of about 250 mg Trx-sBLyS/g DWC (1686 mg Trx-sBLyS/L) and expression level of about 38.5% in soluble Trx-sBLyS were obtained in a 30-1 bioreactor after optimization of the fermentation conditions. After the completion of the optimized purification procedure in order of affinity chromatography, enzymatic cleavage with enterokinase and DEAE ion exchange chromatography, about 200 mg sBLyS per liter fermentation broth was obtained with a purity of about 95% and a yield of near 30%, respectively. Furthermore, the molecular weight (MW) and the isoelectric point (pl) of the purified sBLyS were determined by 2-D gel electrophoresis and SDS-PAGE analysis and estimated to be over 16 kDa and about pH 4.15, respectively. In addition, the bioactivities of the soluble Trx-sBLyS in fermentation broth and the purified sBLyS were tested by two kinds of analytical methods of bioactivity. The good fermentation yield and the satisified, purified sBLyS product with high purity, yield and bioactivity demonstrated the sBLyS production procedure was promising in industry. Published in Russian in Prikladnaya Biokhimiya i Mikrobiologiya, 2008, Vol. 44, No. 2, pp. 187–192. The text was submitted by the authors in English.     

High Efficient Expression of Bioactive Human BMP-14 in <Emphasis Type="Italic">E. coli</Emphasis> Using SUMO Fusion Partner

Bone morphogenetic proteins (BMPs) are cytokines from the TGF-β superfamily, with important roles during embryonic development and in the induction of bone and cartilage tissue differentiation in the adult body. In this contribution, We report here the application of small ubiquitin-related modifier (SUMO) fusion technology to the expression and purification of human BMP-14. The fusion protein expressed in a soluble form was purified to a purity of 90% by Ni-IDA chromatography. After the SUMO-BMP14 fusion protein was cleaved by the SUMO protease at 30 °C for 1 h, the cleaved sample was re-applied to a Ni-IDA. Finally, about 45 mg recombinant hBMP-14 was obtained from 1 litre bacterial culture with no less than 95% purity. The purified hBMP-14 dimer was over 90% purity and could induce the expression of alkaline phosphatase activity in C2C12 cells in a dose-dependent manner. Thus the SUMO-mediated peptide expression and purification system potentially could be employed for the production of other homodimeric proteins.     

SUMO蛋白酶活性片段的表达、纯化及活性测定

利用PCR技术人工合成编码酿酒酵母泛素样特异性蛋白酶1 (Ubiquitin-like specific protease 1,Ulp1)第403到621个氨基酸残基之间的DNA片段Ulp1p,并连接到大肠杆菌表达载体pET-3c中,构建出重组表达质粒pET-Ulp1p。将重组质粒转化至大肠杆菌BL21(DE3)中,氨苄青霉素抗性筛选转化子。经IPTG诱导4h后, SDS-PAGE结果显示,Ulp1p为可溶性表达,表达量占菌体总蛋白的50.8%。通过Ni-NTA凝胶亲和层析和G-25凝胶层析联用可以获得纯度大于95%的Ulp1p。Western-blotting分析表明,Ulp1p能与6xHis抗体产生免疫反应。以重组蛋白SUMO-hEGF(人表皮生长因子)和GST-SUMO-MT(金属硫蛋白)为底物进行酶切分析,结果显示,Ulp1p能特异性水解这两种SUMO融合蛋白,其比活为1.386 x104U/mg。     

Over-Expression in <Emphasis Type="Italic">E. coli</Emphasis> and Purification of the Human OCTN2 Transport Protein

The OCTN2 cDNA amplified from human skin fibroblast was cloned in pET-41a(+) carrying the glutathione S-transferase (GST) gene. The construct pET-41a(+)–hOCTN2 was used to express the GST–hOCTN2 fusion protein in Escherichia coli Rosetta(DE3)pLysS. The best over-expression was obtained after 6 h of induction with IPTG at 28°C. The GST–hOCTN2 polypeptide was collected in the inclusion bodies and showed an apparent molecular mass on SDS-PAGE of 85 kDa. After solubilization with a buffer containing 0.8% sarkosyl and 3 M urea, the fusion protein was applied onto a Ni²⁺-chelating chromatography column. The purified GST–hOCTN2 was treated with thrombin, and the hOCTN2 was separated from the GST by size exclusion chromatography. After the whole procedure, a yield of about 0.2 mg purified protein per liter of cell culture was obtained. To improve the protein yield, hOCTN2 cDNA was subjected to codon bias. The second codon CGG was substituted with AAA; the substitution led to the mutation R2K in the hOCTN2 protein. hOCTN2(R2K) cDNA was cloned in pET-21a(+) carrying a C-terminal 6His tag. The resulting protein was expressed in E. coli Rosetta(DE3)pLysS and purified by Ni²⁺-chelating chromatography. A yield of about 3.5 mg purified protein per liter of cell culture was obtained with this procedure.     

Expression and Purification of a Recombinant “Small” Sialidase fromClostridium perfringensA99

A 1.4-kb gene encoding the “small” sialidase isoenzyme ofClostridium perfringensA99, including its own promoter, was previously cloned in and expressed byEscherichia coliJM 101. Since all attempts to purify this enzyme to homogeneity were unsuccessful, a new strategy was developed. The structural gene was amplified by means of a PCR technique and inserted into the plasmid vector pQE-10, transferring a six-histidine affinity tag (His₆) to the N-terminus of the protein. In order to minimize proteolytic degradation of the sialidase protein, the gene was subcloned into theEscherichia colistrain BL21(DE3)pLys S with reduced protease activity. The sialidase production was increased about 2.5-fold when compared with that of the original clone. The enzyme, released by lysozyme treatment of the bacterial cells, was purified by metal chelate chromatography on Ni–nitrilo-triacetic acid agarose to apparent homogeneity in SDS–PAGE. The 42-kDa protein was enriched 62-fold with a yield of 82% and a specific activity of 280 U mg⁻¹. A total amount of 1 mg sialidase was obtained from 1 liter of bacterial culture. For future studies, including crystallization experiments, the histidine affinity tag was removed from the sialidase enzyme by aminopeptidase K. The sialidase was then separated from aminopeptidase K by ion-exchange chromatography, resulting in an overall yield of 83% and a specific activity of 305 U mg⁻¹using 4-methylumbelliferyl-α- -N-acetylneuraminic acid under standard conditions. The two forms (with or without the histidine tag) of sialidase exhibited similar kinetic properties when compared to the wild-type enzyme.     

Use of dual affinity tags for expression and purification of functional peripheral cannabinoid receptor

The human peripheral cannabinoid receptor (CB2) was expressed as a fusion with the maltose-binding protein (at the N-terminus), thioredoxin A (at the C-terminus) and two small affinity tags (a Strep-tag and a polyhistidine tag). Expression levels of the recombinant receptor in Escherichia coli BL21(DE3) cells were dependent on location and type of tags in the expression construct, and were as high as 1-2mg per liter of bacterial culture. The recombinant receptor was ligand binding-competent, and activated cognate G-proteins in an in vitro coupled assay. The fusion CB2-125 protein was purified by immobilized metal affinity chromatography on a Ni-NTA resin. Maltose-binding protein, thioredoxin and a decahistidine tag were removed from the fusion by treatment with Tobacco etch virus (Tev) protease. Purification to over 90% homogeneity of the resulting CB2, containing an N-terminal Strep-tag was achieved by affinity chromatography on a StrepTactin resin. Circular dichroism spectroscopy indicated an alpha-helical content of the purified recombinant protein of approximately 54%. The expression and purification protocol allows for production of large (milligram) quantities of functional peripheral cannabinoid receptor, suitable for subsequent structural characterization. Preliminary results of reconstitution experiments indicate that the CB2 has retained its ligand-binding properties.     

High-level expression, purification and pro-apoptosis activity of HIV-TAT-survivin (T34A) mutant to cancer cells in vitro

Survivin, a novel member of the IAP family, was observed to express in the most common human cancers. Anti-cancer therapy targeting survivin had drawn considerable attention. This study focused on high-level expression of recombinant protein TAT-survivin (T34A) mutant in E. coli, purification and bioactivity of pro-apoptosis to various cell lines in vitro. The cDNA encoding survivin was cloned by RT-PCR from breast cancer cell lines B-cap37. After PCR site-directed mutagenesis and construction of expression vector pRSET-B-TAT-survivin (T34A), targeted TAT-survivin (T34A) protein was expressed highly in E. coli BL21 (DE3) by 0.5mM IPTG induction and its yield could reach 650 mg/l in fermentation culture. The fusion protein in a form of inclusion body was then solubilized, refolded and purified to a purity of 98% by cation exchange chromatography and size-exclusion chromatography. Four hundred and eighty milligrams protein of interest was obtained in per liter fermentation culture. This showed that the efficient procedures of large-scale expression and purification were successful for the mass production of the recombinant protein. Pro-apoptosis effects of target protein on four cancer cell lines and one normal cell line from human were confirmed by the change of morphology, and pro-apoptosis activity was evaluated by MTT, fluorescent staining of nuclei and flow cytometry assay. Results indicated that B-cap37 and SW1990 were very sensitive to TAT-survivin (T34A) protein. This finding revealed the recombinant protein was promising as an anti-cancer drug.     

Construction, expression, and purification of HIV-TAT-survivin (T34A) mutant: a pro-apoptosis protein in Escherichia coli

As a novel member of the IAP family, survivin was observed to express in the most common human cancers. Anti-cancer therapy targeting survivin has drawn considerable attention. This report presented firstly construction of recombinant plasmid pRSET-B-TAT-survivin (T34A), expression in Escherichia coli, purification, renaturation, and bioactivity. The cDNA encoding survivin was cloned by RT-PCR from breast cancer cell lines B-cap37. Expression vector pRSET-B-TAT-survivin (T34A) was constructed by PCR after survivin was mutated by PCR site-directed mutagenesis. Recombinant TAT-survivin (T34A) protein was expressed highly in E. coli BL21 (DE3) by 0.5 mM IPTG induction and its yield could reach 650 mg/l in fermentation culture. The fusion protein in a form of inclusion body was then solubilized, refolded, and purified to a purity of 98% by cation exchange chromatography and size-exclusion chromatography. Four hundred and eighty milligrams protein of interest was obtained in per liter fermentation culture. The protein of interest was identified by SDS-PAGE and Western blot analysis, and great bioactivity of target protein to two cancer cell lines was confirmed by morphological changes and evaluated by MTT. The findings suggested that recombinant protein TAT-survivin (T34A) has a bright future in cancer therapy targeting towards survivin, and the efficient procedure of expression and purification may be useful for the mass production of this therapeutically important protein.     

基因重组Echistatin发酵工艺的优化

目的:利用基因工程方法对一种蛇毒锯鳞蝰素蛋白的发酵纯化工艺进行优化,以提高目的蛋白的产量和纯度。方法:对工程菌进行发酵培养并诱导表达,研究不同的培养基、不同补料方式、溶解氧浓度、培养和诱导时间对工程菌产量和目的蛋白表达量的影响,利用几丁质亲和层析纯化Ecs融合蛋白,通过合适温度和pH裂解融合蛋白得到Ecs纯品,并鉴定和检测Ecs活性。结果:经过高密度发酵优化后,菌体湿重可达110g/L,目的蛋白表达量约占总蛋白的40%;亲和层析纯化后,得到Ecs单体,得率为68mg/L发酵液。生物学活性分析显示,重组Ecs能有效抑制血小板的聚集,其活性与天然Ecs相似。结论:通过发酵和纯化工艺优化,大大提高了目的蛋白产量,为进一步规模化研究和生产奠定了基础。     

Expression and purification of soluble B lymphocyte stimulator from recombinant Escherichia coli

In this work, the expression conditions of fusion protein thioredoxin (Trx)-soluble B lymphocyte stimulator (sBLyS) in shake flask and bioreactor from the recombinant Escherichia coli BL21 (DE3) with a pET system encoding the fusion protein gene of Trx-sBLyS and the purification method of the sBLyS were optimized to effectively obtain the bioactive protein sBLyS with a high purity. A yield of about 250 mg Trx-sBLyS/g DWC (1686 mg Trx-sBLyS/L) and expression level of about 38.5% in soluble Trx-sBLyS were obtained in a 30 1 bioreactor after optimization of the fermentation conditions. After the completion of the optimized purification procedure in order of affinity chromatography, enzymatic cleavage with enterokinase and DEAE ion exchange chromatography, about 200 mg sBLyS per liter fermentation broth was obtained with a purity of about 95% and a yield of near 30%, respectively. Furthermore, the molecular weight (MW) and the isoelectric point (pI) of the purified sBLyS were determined by 2-D gel electrophoresis and SDS-PAGE analysis and estimated to be over 16 kDa and about pH 4.15, respectively. In addition, the bioactivities of the soluble Trx-sBLyS in fermentation broth and the purified sBLyS were tested by two kinds of analytical methods of bioactivity. The good fermentation yield and the satisfied, purified sBLyS product with high purity, yield and bioactivity demonstrated the sBLyS production procedure was promising in industry.     

Expression and purification of hexahistidine-tagged human glutathione S-transferase P1-1 in Escherichia coli

The bacterial expression and purification of human pi class glutathione S-transferase (hGST P1-1) as a hexahistidine-tagged polypeptide was performed. The expression plasmid for hGST P1-1 was constructed by ligation of the cDNA which codes for the protein into the expression vector pET-15b. The expressed protein was purified by either glutathione or metal (Co(2+)) affinity column chromatography, which produced the pure and fully active enzyme in one step with a yield of more than 30 mg/liter culture. The activity of the purified protein was 130 units mg(-1) from the GSH affinity column and 112 units mg(-1) from the Co(2+) affinity column chromatography. The purity of the protein was assessed by electrospray ionization mass spectrometry and size-exclusion chromatography. It showed that the real molecular weight of the hexahistidine-tagged hGST P1-1 polypeptide chain agreed with the calculated value and that the purified protein eluted as an apparent homodimer on the gel filtration column. Our expression system allows the expression and purification of active hexahistidine-tagged hGST P1-1 in high yield with no need of removal of the hexahistidine tag and gives pure protein in one purification step allowing further study of this enzyme.     

An improved strategy for high-level production of human vasostatin120-180

We previously reported a strategy for expression and purification of human Vasostatin120-180 (VAS), a potent angiogenesis inhibitor in a GST fusion form; however, the yield of 7.2 mg per liter of culture was relatively low. The aim of this study was to develop a more efficient system to improve and facilitate the production of VAS protein in a soluble and native form in Escherichia coli. The VAS gene with optimized condons was cloned into pET28a and overexpressed as a N-terminal His-tagged fusion protein. Between His-tag and VAS, an enterokinase recognition site was introduced to release the intact VAS. Optimal expression of soluble His-VAS was achieved by examining the contribution of chaperone coexpression and lower temperature fermentation. Ammonium sulfate precipitation was first employed to remove nucleic acid and partial host proteins. When further purified by Ni2+ affinity chromatography, 40 mg of His-VAS was isolated with purity over 85% from 1 L of culture. After desalting with Sephadex G15 and digestion with His-EK, followed by the removal of the His-tag and His-EK with Ni(2+)-NTA resin, 21 mg of intact VAS was finally obtained from 1 L of bacterial culture, which was approximately 3-fold the yield we previously obtained via GST fusion expression strategy. The identity of His-VAS and VAS was confirmed by Western blot. Purified VAS displayed distinct anti-angiogenic activity, which was shown by the endothelial cell proliferation inhibition assay and chicken chorioallantoic membrane assay. In sum, we greatly improved the yield of intact and bioactive VAS protein, and using this successful example, we propose a more efficient system for the high-level production of intact functional proteins, especially for low molecule weight peptides.     

High-level expression and characterization of an anti-VEGF165 single-chain variable fragment (scFv) by small ubiquitin-related modifier fusion in <Emphasis Type="Italic">Escherichia coli</Emphasis>

Antibodies currently constitute the most rapidly growing class of human therapeutics; however, the high-yield production of recombinant antibodies and antibody fragments is a real challenge. High expression of active single-chain antibody fragment (scFv) in Escherichia coli has not been successful, as the protein contains three intramolecular disulfide bonds that are difficult to form correctly in the bacterial intracellular environment. To solve this problem, we fused the scFv gene against VEGF165 with a small ubiquitin-related modifier gene (SUMO) by synthesizing an artificial SUMO–scFv fusion gene that was highly expressed in the BL21(DE3) strain. The optimal expression level of the soluble fusion protein, SUMO–scFv, was up to 28.5% of the total cellular protein. The fusion protein was purified by Ni nitrilotriacetic acid (NTA) affinity chromatography and cleaved by a SUMO-specific protease to obtain the native scFv, which was further purified by Ni-NTA affinity chromatography. The result of the high-performance liquid chromatography showed that the purity of the recombinant cleaved scFv was greater than 98%. The primary structure of the purified scFv was confirmed by N-terminal amino acid sequencing and matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy analysis. In vitro activity assay demonstrated that the recombinant scFv could dose-dependently inhibit VEGF165-induced human umbilical vein-derived endothelial cell proliferation. The expression strategy presented in this study allows convenient high yield and easy purification of recombinant scFv with native sequences.