Study of rabies virus by Differential Scanning Calorimetry

Differential Scanning Calorimetry (DSC) has been used in the past to study the thermal unfolding of many different viruses. Here we present the first DSC analysis of rabies virus. We show that non-inactivated, purified rabies virus unfolds cooperatively in two events centered at approximately 62 and 73 °C. Beta-propiolactone (BPL) treatment does not alter significantly viral unfolding behavior, indicating that viral inactivation does not alter protein structure significantly. The first unfolding event was absent in bromelain treated samples, causing an elimination of the G-protein ectodomain, suggesting that this event corresponds to G-protein unfolding. This hypothesis was confirmed by the observation that this first event was shifted to higher temperatures in the presence of three monoclonal, G-protein specific antibodies. We show that dithiothreitol treatment of the virus abolishes the first unfolding event, indicating that the reduction of G-protein disulfide bonds causes dramatic alterations to protein structure. Inactivated virus samples heated up to 70 °C also showed abolished recognition of conformational G-protein specific antibodies by Surface Plasmon Resonance analysis. The sharpness of unfolding transitions and the low standard deviations of the Tm values as derived from multiple analysis offers the possibility of using this analytical tool for efficient monitoring of the vaccine production process and lot to lot consistency.     

Purification of truncated and mutated Chemotaxis Inhibitory Protein of Staphylococcus aureus--an anti-inflammatory protein

The Chemotaxis Inhibitory Protein of Staphylococcus aureus (CHIPS) binds and blocks the C5a receptor (C5aR) and formyl-peptide receptor (FPR). This way, CHIPS is a potent inhibitor of the immune cell recruitment associated with inflammation. Truncation of the protein and the introduction of mutations, shifts the expression towards the insoluble fraction of Escherichia coli, whereas the wild-type protein can be solubly expressed. A protocol for expression and tag independent purification of biologically active CHIPS variants has been established to enable further characterization of an improved CHIPS variant, called ADC-1004. The CHIPS variants were purified by washing of E. coli inclusion bodies followed by refolding and gel filtration. New techniques were utilized to optimize the purification process. Expression in inclusion bodies was increased by the use of Ultra Yield^™ flasks and optimal refolding conditions were determined by the use of the iFOLD Refolding System 2^™.The folding and biological activity of the purified proteins were analyzed by circular dichroism (CD) spectroscopy and flow cytometry, respectively, and compared to solubly produced CHIPS_31–113 and wild-type CHIPS_1–121. We show that the CHIPS variants produced in inclusion bodies can be refolded and purified to achieve equal biological activity as solubly produced CHIPS_31–113 and wild-type CHIPS_1–121. The truncation causes minor structural changes while purification from inclusion bodies or the soluble fraction does not further affect the structure.     

Development of a simple fed-batch process for the high-yield production of recombinant Japanese encephalitis virus protein

Japanese encephalitis (JE) is one of the leading causes of acute encephalopathy affecting children and adolescents in the tropics. Optimization of media was carried out for enhanced production of recombinant JE virus envelope domain III (EDIII) protein in Escherichia coli. Furthermore, batch and fed-batch cultivation process in E. coli was also developed in optimized medium. Expression of this protein in E. coli was induced with 1 mM isopropyl-β-thiogalactoside and yielded an insoluble protein aggregating to form inclusion bodies. The inclusion bodies were solubilized in 8 M urea, and the protein was purified under denaturing conditions using Ni-NTA affinity chromatography. After fed-batch cultivation, the recombinant E. coli resulted in cell dry weight and purified protein about 36.45 g l⁻¹ and 720 mg l⁻¹ of culture, respectively. The purity of the recombinant JE virus EDIII protein was checked by sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis, and reactivity of this protein was determined by Western blotting and ELISA with JE virus-infected human serum samples. These results establish the application of this protein to be used for the diagnosis of JE virus infection or for further studies in vaccine development. This process may also be suitable for the high-yield production of other recombinant viral proteins.     

Expression of Coat Protein of an Ordinary Strain of Potato virus Y in Escherichia coli and Production of Polyclonal Antibodies for Diagnosis

The coat protein gene (CP) of an ordinary strain of Potato virus Y (PVY^O) was cloned into the expression vector, pET‐28a(+). The insert was sequenced and analysis showed that the CP gene was in frame with intact N‐terminal 6X histidine tags. An approximately 35 kDa recombinant fusion protein was observed in inclusion bodies of induced Escherichia coli BL21 cells. This fusion protein was purified and used as antigen to raise polyclonal antibodies in rabbits. In Western blot and dot blot immuno‐binding assay (DIBA), both PVY^O‐CP IgG and PVY^O IgG strongly reacted with the recombinant CP. The PVY^O‐CP IgG could detect PVY^O in infected samples up to 1 : 3200 dilutions. A PVY^O‐CP ELISA kit was prepared and compared with conventional ELISA kit based on purified virus particles (PVY^O ELISA kit). The PVY^O‐CP ELISA kit consistently detected the PVY^O in DAS‐ELISA of field samples and was as effective as PVY^O ELISA kit.     

人源抗狂犬病毒单克隆抗体Fab段基因的获得和表达

运用噬菌体表面呈现（phage display）技术获得了人源抗狂犬病毒糖蛋白基因工程单克隆抗体Fab段基因及其表达。从狂犬病毒PM株Vero细胞疫苗免疫的人抗凝血中分离获得外周淋巴细胞,提取细胞总RNA,通过RTPCR方法,用一组人IgG Fab基因4特异性引物,从合成的cDNA中扩增了一组轻链和重链Fab段基因,将轻链和重链Fab段基因,将轻链和重链先后克隆入噬菌体载体pComb3,成功地建立了抗狂犬病毒抗原的方法,对此抗体库进行富积筛选表达,成功地获得了抗狂犬病毒的人源单抗Fab段基因及其在大肠杆菌中的有效表达,对其中一株单抗G10进行了较为系统的分析,发现它与一株鼠源中和性狂犬病毒糖蛋白特异性单抗存在竞争,证实该单抗能识别狂犬病毒糖蛋白,其序列资料分析表明,该单抗为一株新的抗狂犬病毒人源基因工程抗体。     

重组人抗狂犬病病毒单抗SO57、SOJB对不同狂犬病病毒毒株中和作用的研究

用不同的动物模型研究了具有专利的重组人抗狂犬病病毒单克隆抗体SO57、SOJB对不同狂犬病病毒株的中和作用,100IU/kg的SO57能100%保护被中国街毒株SBD攻击的中国仓鼠;首次用小鼠模型模拟人体被狂犬病病毒攻击后的治疗情况,在小鼠被CVS及中国街毒代表株攻击后,SO57与HRIG具有相近的对小鼠的暴露后保护作用;同时结果显示HRIG对SBD株攻击的保护率不能到达100%,仅使用疫苗是不能对感染病毒的小鼠百分之百的保护;SOJB与SO57 1:1联合使用未显示比SO57单独使用更好的保护效果。SO57极有可能在中国代替HRIG用于狂犬病病毒暴露后治疗。     

Optimized procedures for producing biologically active chemokines

We describe here two strategies to produce biologically active chemokines with authentic N-terminal amino acid residues. The first involves producing the target chemokine with an N-terminal 6×His-SUMO tag in Escherichia coli as inclusion bodies. The fusion protein is solubilized and purified with Ni–NTA–agarose in denaturing reagents. This is further followed by tag removal and refolding in a redox refolding buffer. The second approach involves expressing the target chemokine with an N-terminal 6×His-Trx-SUMO tag in an engineered E. coli strain that facilitates formation of disulfide bonds in the cytoplasm. Following purification of the fusion protein via Ni–NTA and tag removal, the target chemokine is refolded without redox buffer and purified by reverse phase chromatography. Using the procedures, we have produced more than 15 biologically active chemokines, with a yield of up to 15 mg/L.     

Clinical grade production and characterization of a fusion protein comprised of the chemokine CCL2-ligand genetically fused to a mutated and truncated form of the Shiga A1 subunit

First generation chemokine ligand-Shiga A1 (SA1) fusion proteins (leukocyte population modulators, LPMs) were previously only obtained in small quantities due to the ribosomal inactivating protein properties of the SA1 moiety which inhibits protein synthesis in host cells. We therefore employed 4-aminopyrazolo[3,4-d]-pyrimidine, an inhibitor of Shiga A1, to allow the growth of these cells prior to induction and during the expression phase post-induction with IPTG. Scale-up allowed the production of gram quantities of clinical grade material of the lead candidate, OPL–CCL2–LPM. A manufacturing cell bank was established and used to produce OPL–CCL2–LPM in a fed-batch fermentation process. Induction of the expression of OPL–CCL2–LPM led to the production of 22.47 mg/L per OD₆₀₀ unit. The LPM was purified from inclusion bodies using solubilization, renaturation, refolding and chromatography steps. The identity and purity of the OPL–CCL2–LPM was determined using several analytical techniques. The product retained the ability of the SA1 moiety to inhibit protein synthesis as measured in a rabbit reticulocyte lysate cell-free protein synthesis assay and was cytotoxic to target cells. Binding studies established that the protein exerts its effects via CCR2, the cognate receptor for CCL2. Clinical trials in inflammatory nephropathies are planned.     

Studies on Rabies Virus RNA Polymerase: 1. cDNA Cloning of the Catalytic Subunit (L Protein) of Avirulent HEP-Flury Strain and Its Expression in Animal Cells

To investigate the RNA polymerase of rabies virus, we cloned a cDNA of the catalytic subunit (called L protein because of its large molecular size) of the HEP-Flury strain, an avirulent strain obtained by high frequencies of serial embryonated hen egg passages. Nucleotide sequencing showed that the cDNA encodes a long polypeptide of 2,127 amino acids (Mr. 242,938). A comparison of the deduced amino acid sequence with that of other strains (PV and SAD B19) indicated that the sequence was highly conserved, except for several amino acid substitutions which were accumulated in some limited regions. A fragment of the cDNA was used for expression in Escherichia coli (E. coli) to prepare the L antigen for raising the antibodies in rabbits. Immunoprecipitation studies with the rabbit antiserum showed that the polypeptides produced in the L cDNA-transfected COS-7 cells displayed almost the same electrophoretic mobility as that of authentic L protein. Immunofluorescence studies indicated that both L and P (another subunit of RNA polymerase) proteins displayed colocalized distribution with the nucleocapsid antigen (N) in the cytoplasmic inclusion bodies, where envelope proteins (G and M) were absent. On the other hand, expression of the L protein alone did not cause inclusion body-like granular distribution, suggesting that the inclusion body-like accumulation depends on certain interaction(s) with other viral gene products, probably with the ribonucleoproteins comprising the inclusion bodies.     

狂犬病毒核蛋白（NP）的纯化及其免疫原性的研究

对重组痘苗毒和重杆状病毒表达的狂犬病毒NP及原代地鼠肾细胞培养的狂犬病毒核衣壳蛋白（RNP）、先经Sepharose CL 4B分子筛柱初步提纯,再经抗狂犬病毒NP McAB 2C12-S-epharose 4B亲和层析柱纯化分离,经ELISA、SDS－PAGE电泳和Western-Blot分析证实,获得了高纯度和免疫反应性的NP和RNP。以相同剂量的纯化蛋白免疫小鼠,RNP和两种重组NP均可诱生特异的抗NP抗体,三种蛋白间无明显差异;狂犬病毒CVS株攻击保护实验结果显示,三种蛋白免疫的小鼠存活率约为50％;两种重组NP的免疫反应性和免疫原性与天然狂犬病毒RNP相似。     

Identification of binding epitope for anti-rabies virus glycoprotein single-chain Fv fragment FV57

Single-chain Fv fragment (scFv) of anti-rabies glycoprotein (G protein) has been recommended as a new agent for detecting and neutralizing lethal rabies virus. In this study, we constructed scFv that corresponded to the FV fragment of CR57, a monoclonal antibody against rabies virus, and called it FV57. Despite its virus neutralization activity, FV57 may or may not recognize the same epitope as that recognized by CR57. To resolve this issue, the binding epitope of rabies virus G protein recognized by FV57 was identified. A recombinant rabies virus G protein fragment (RVG179; residues 179-281) comprising several epitopes was expressed in E.coli, purified, and the specificity of its binding with FV57 was determined. In addition, a peptide (abbreviated as EP, residues 224-236) comprising the known epitope of G protein to which CR57 binds was synthesized and the potency of its binding with FV57 was also determined. The results showed that FV57 could specifically bind to RVG179 and EP. Competitive ELISA experiments indicated that RVG179 and EP were able to compete with the rabies virus G protein for binding with FV57. Since no other epitope within residues 224- 236 has been reported, except for the epitope to which CR57 binds (residues 226-231), the epitope recognized by FV57 was the same as its intact antibody CR57. This demonstrated that the complementarity-determining regions (CDRs) of the heavy and light chains of FV57 have folded into the correct conformation as those of CR57.     

Production enhancement and refolding of caprine growth hormone expressed in Escherichia coli

This study describes comparison between IPTG and lactose induction on expression of caprine growth hormone (cGH), enhancing cell densities of Escherichia coli cultures and refolding the recombinant cGH, produced as inclusion bodies, to biologically active state. 2–3 times higher cell densities were obtained in shake flask cultures when induction was done with lactose showing almost same level of expression as in case of IPTG induction. With lactose induction highest cell densities were achieved in TB (OD₆₀₀ 16.3) and M9NG (OD₆₀₀ 16.1) media, producing 885 and 892 mg cGH per liter of the culture, respectively. Lactose induction done at mid-exponential stage resulted in a higher cell density and thus higher product yield. cGH over-expressed as inclusion bodies was solubilized in 50 mM Tris–Cl buffer (pH 12.5) containing 2 M urea, followed by dilution and lowering the pH in a step-wise manner to obtain the final solution in 50 mM Tris–Cl (pH 9.5). The cGH was purified by Q-Sepharose chromatography followed by gel filtration with a recovery yield of 39% on the basis of total cell proteins. The product thus obtained showed a single band by SDS–PAGE analysis. MALDI-TOF analysis showed a single peak with a mass of 21,851 dalton, which is very close to its calculated molecular weight. A bioassay based on proliferation of Nb2 rat lymphoma cells showed that the purified cGH was biologically active.     

Preparation and identification of anti-rabies virus monoclonal antibodies

To provide a foundation for the development of rapid and specific methods for the diagnosis of rabies virus infection,anti-rabies virus monoclonal antibodies were prepared and rabies virus nucleoprotei...     

Single Domain Antibody Multimers Confer Protection against Rabies Infection

Post-exposure prophylactic (PEP) neutralizing antibodies against Rabies are the most effective way to prevent infection-related fatality. The outer envelope glycoprotein of the Rabies virus (RABV) is the most significant surface antigen for generating virus-neutralizing antibodies. The small size and uncompromised functional specificity of single domain antibodies (sdAbs) can be exploited in the fields of experimental therapeutic applications for infectious diseases through formatting flexibilities to increase their avidity towards target antigens. In this study, we used phage display technique to select and identify sdAbs that were specific for the RABV glycoprotein from a naïve llama-derived antibody library. To increase their neutralizing potencies, the sdAbs were fused with a coiled-coil peptide derived from the human cartilage oligomeric matrix protein (COMP48) to form homogenous pentavalent multimers, known as combodies. Compared to monovalent sdAbs, the combodies, namely 26424 and 26434, exhibited high avidity and were able to neutralize 85-fold higher input of RABV (CVS-11 strain) pseudotypes in vitro, as a result of multimerization, while retaining their specificities for target antigen. 26424 and 26434 were capable of neutralizing CVS-11 pseudotypes in vitro by 90–95% as compared to human rabies immunoglobulin (HRIG), currently used for PEP in Rabies. The multimeric sdAbs were also demonstrated to be partially protective for mice that were infected with lethal doses of rabies virus in vivo. The results demonstrate that the combodies could be valuable tools in understanding viral mechanisms, diagnosis and possible anti-viral candidate for RABV infection.     

Expression, purification and characterization of pectin methylesterase inhibitor from kiwi fruit in Escherichia coli

A significant problem in production of fruit juices for human consumption is auto-clarification, where enzyme catalyzes pectin demethylation resulting in loss of the ‘‘natural” cloudy appearance of juices. To overcome this problem, a plant inhibitor protein which blocks the action of pectin methylesterase has been used. In this paper, expression of recombinant kiwi pectin methylesterase inhibitor (PMEI) was carried out in Escherichia coli, and the target protein was expressed in the form of inclusion bodies. The expression level reached 46% of total cell protein. Then the fusion protein was purified by nickel ion metal affinity chromatography, and the purity was finally up to 98%. After refolding in GSH/GSSG redox system, recombinant PMEI not only could efficiently inhibit PMEs from eight different plants, but could remain effective inhibitor activity in the pH 3.0–10.0 and 20–40 °C. Thus, recombinant PMEI has potential application in the production of fruit juices product industry.     

The influence of homologous vs. heterologous challenge virus strains on the serological test results of rabies virus neutralizing assays

The effect that the relatedness of the viral seed strain used to produce rabies vaccines has to the strain of challenge virus used to measure rabies virus neutralizing antibodies after vaccination was evaluated. Serum samples from 173 subjects vaccinated with either purified Vero cell rabies vaccine (PVRV), produced from the Pittman Moore (PM) seed strain of rabies virus, or purified chick embryo cell rabies vaccine (PCECV), produced from the Flury low egg passage (Flury-LEP) seed strain of rabies virus, were tested in parallel assays by RFFIT using a homologous and a heterologous testing system. In the homologous system, CVS-11 was used as the challenge virus in the assay to evaluate the humoral immune response in subjects vaccinated with PVRV and Flury-LEP was used for subjects vaccinated with PCECV. In the heterologous system, CVS-11 was used as the challenge virus in the assay to evaluate subjects vaccinated with PCECV and Flury-LEP was used for subjects vaccinated with PVRV. Although the difference in G protein homology between the CVS-11 and Flury-LEP rabies virus strains has been reported to be only 5.8%, the use of a homologous testing system resulted in approximately 30% higher titers for nearly two-thirds of the samples from both vaccine groups compared to a heterologous testing system. The evaluation of equivalence of the immune response after vaccination with the two different vaccines was dependent upon the type of testing system, homologous or heterologous, used to evaluate the level of rabies virus neutralizing antibodies. Equivalence between the vaccines was achieved when a homologous testing system was used but not when a heterologous testing system was used. The results of this study indicate that the strain of virus used in the biological assays to measure the level of rabies virus neutralizing antibodies after vaccination could profoundly influence the evaluation of rabies vaccines.     

Production of Polyclonal Antibodies to the Recombinant Potato virus M (PVM) Non‐structural Triple Gene Block Protein 1 and Coat Protein

The genes encoding the coat protein (CP) and triple gene block protein 1 (TGBp1) of Potato virus M (PVM) were cloned into expression vector pET‐45b(+) (N‐terminal 6xHis tag) and expressed in E. coli Rosetta gami‐2(DE3). The purified recombinant antigens were used for raising polyclonal antibodies. The antibodies against recombinant CP were successfully used in Western blot analysis, plate‐trapped ELISA and DAS‐ELISA as a coating for PVM detection in infected potato leaf samples. The antibodies against recombinant non‐structural protein detected the TGBp1 only in Western blot analysis. This is the first report of the production of polyclonal antibodies against recombinant coat protein and TGBp1 of PVM and their use for detecting the virus.     

Purification of the Caenorhabditis elegans Transposase Tc1A Refolded during Gel Filtration Chromatography

Full-length recombinant transposase Tc1A from Caenorhabditis elegans (343 amino acids) expressed in Escherichia coli BL21 in inclusion bodies has been purified in a high yield in a soluble form. The procedure includes denaturation of the inclusion bodies followed by refolding of the Tc1A protein by gel filtration. This last step is absolutely crucial to give a high yield of soluble and active protein since it allows the physical separation of the aggregates from intermediates that give rise to correctly refolded protein. This step is very sensitive to the concentration of protein. Good yields of refolded protein are obtained by refolding 2 to 12 mg of denatured protein. The other purification steps involve the initial use of gel filtration under denaturing conditions and a final step of ion-exchange chromatography. Biological activity of the purified protein was confirmed in an in vitro transposon excision assay and its DNA-binding capacity by UV crosslinking. This new Tc1A purification procedure gives a yield of 12–16 mg/liter E. coli culture, in a form suitable for crystallization studies.     

In vitro propagation of plant virus using different forms of plant tissue culture and modes of culture operation

Plant virus accumulation was investigated in vitro using three different forms of plant tissue culture. Suspended cells, hairy roots and shooty teratomas of Nicotiana benthamiana were infected with tobacco mosaic virus (TMV) using the same initial virus:biomass ratio. Viral infection did not affect tissue growth or morphology in any of the three culture systems. Average maximum virus concentrations in hairy roots and shooty teratomas were similar and about an order of magnitude higher than in suspended cells. Hairy roots were considered the preferred host because of their morphological stability in liquid medium and relative ease of culture. The average maximum virus concentration in the hairy roots was 0.82 ± 0.14 mg g⁻¹ dry weight; viral coat protein represented a maximum of approximately 6% of total soluble protein in the biomass. Virus accumulation in hairy roots was investigated further using different modes of semi-continuous culture operation aimed at prolonging the root growth phase and providing nutrient supplementation; however, virus concentrations in the roots were not enhanced compared with simple batch culture. The relative infectivity of virus in the biomass declined by 80–90% during all the cultures tested, irrespective of the form of plant tissue used or mode of culture operation. Hairy root cultures inoculated with a transgenic TMV-based vector in batch culture accumulated green fluorescent protein (GFP); however, maximum GFP concentrations in the biomass were relatively low at 39 μg g⁻¹ dry weight, probably due to genetic instability of the vector. This work highlights the advantages of using hairy roots for in vitro propagation of TMV compared with shooty teratomas and suspended plant cells, and demonstrates that batch root culture is more effective than semi-continuous operations for accumulation of high virus concentrations in the biomass.     

狂犬病毒aG株糖蛋白在pET原核系统中的表达及纯化

在狂犬病的临床诊断和基础研究中都迫切需要大量纯度高且价廉的狂犬病毒糖蛋白抗原。本文应用带有Ｈｉｓ６尾的ｐＥＴ原核表达系统对狂犬病毒（ＲＶ）ａＧ株的糖蛋白（ＧＰ）进行表达和纯化。构建的融合表达载体ｐＥＴ－ａＧ１和ｐＥＴ－ａＧ２（－５７ｂｐ）分别含有ＲＶａＧ株ＧＰ基因的全序列及删除了为ＧＰ信号肽编码的５８个碱基的序列。用ＳＤＳ 聚丙烯酰胺凝胶电泳、免疫印迹、间接ＥＬＩＳＡ检测都证明表达产物为ＲＶＧＰ,且位于菌体中的包涵体内。经固定化金属螯合层析（ＩＭＡＣ）提纯,ｐＥＴ－ａＧ１表达产物有较高的特异性和纯度,可用作测定ＲＶＧＰ抗体的免疫诊断试剂。