Secretion of active recombinant human tissue plasminogen activator derivatives in Escherichia coli

Response Surface Methodology to Optimize the Expression Efficiency of Recombinant Reteplase

Background

Over expression of Reteplase enzyme has already been studies in the periplasmic space of Escherichia coli (E. coli). However, the role different factors in its expresssin rate remained to be elucidated.

Objectives

Optical cell density (OD), IPTG concentration, and expression time are highly effective in the protein expression rates. Therefore, we aimed to determine the optimum levels of these factors for reteplase expression using response surface methodology (RSM).

Materials and Methods

The pET21b plasmid was used to sub-clone the designed reteplase gene. Then, the gene was transformed into E. coli BL21 strain. Induction of expression was done by IPTG and analyzed by the SDS page. experiments were designed using the RMS, while the effects of different conditions were evaluated using the Real time-PCR.

Results

Sequence optimization removed all undesirable sequences of the designed gene. Transformation into E. coli BL21 was confirmed with an 1152 bp band on the agarose gel. A 39 kDa expression band on the SDS gel confirmed the gene expression. Performing 20 RSM-designed experiments, the optimum levels for IPTG concentration and OD were determined as 0.34mM and 5.6, respectively. Moreover, the optimum level of expression time was demonstrated to be 11.91 hours. The accuracy of the regression model for reteplase overexpression was confirmed by an F-value equal to 25.31 and a meager probability value [(Prob > F) < 0.0001]. The real-time-PCR results indicated that the performed calculations were highly accurate.

Conclusion

The obtained results indicate that IPTG concentration, OD, and expression time are significantly involved in the augmentation of recombinant reteplase expression. To the best of our knowledge, this is the first study to assess the combined effect of these factors on reteplase expression. Further RSM-based experiments would bring about new insights regarding the best conditions for reteplase expression.

Reteplase: Structure, Function, and Production

Thrombolytic drugs activate plasminogen which creates a cleaved form called plasmin, a proteolytic enzyme that breaks the crosslinks between fibrin molecules. The crosslinks create blood clots, so reteplase dissolves blood clots. Tissue plasminogen activator (tPA) is a well-known thrombolytic drug and is fibrin specific. Reteplase is a modified nonglycosylated recombinant form of tPA used to dissolve intracoronary emboli, lysis of acute pulmonary emboli, and handling of myocardial infarction. This protein contains kringle-2 and serine protease domains. The lack of glycosylation means that a prokaryotic system can be used to express reteplase. Therefore, the production of reteplase is more affordable than that of tPA. Different methods have been proposed to improve the production of reteplase. This article reviews the structure and function of reteplase as well as the methods used to produce it.

Enzymes approved for human therapy: indications, mechanisms and adverse effects

Research and drug developments fostered under orphan drug product development programs have greatly assisted the introduction of efficient and safe enzyme-based therapies for a range of rare disorders. The introduction and regulatory approval of 20 different recombinant enzymes has enabled, often for the first time, effective enzyme-replacement therapy for some lysosomal storage disorders, including Gaucher (imiglucerase, taliglucerase, and velaglucerase), Fabry (agalsidase alfa and beta), and Pompe (alglucosidase alfa) diseases and mucopolysaccharidoses I (laronidase), II (idursulfase), IVA (elosulfase), and VI (galsulfase). Approved recombinant enzymes are also now used as therapy for myocardial infarction (alteplase, reteplase, and tenecteplase), cystic fibrosis (dornase alfa), chronic gout (pegloticase), tumor lysis syndrome (rasburicase), leukemia (L-asparaginase), some collagen-based disorders such as Dupuytren's contracture (collagenase), severe combined immunodeficiency disease (pegademase bovine), detoxification of methotrexate (glucarpidase), and vitreomacular adhesion (ocriplasmin). The development of these efficacious and safe enzyme-based therapies has occurred hand in hand with some remarkable advances in the preparation of the often specifically designed recombinant enzymes; the manufacturing expertise necessary for commercial production; our understanding of underlying mechanisms operative in the different diseases; and the mechanisms of action of the relevant recombinant enzymes. Together with information on these mechanisms, safety findings recorded so far on the various adverse events and problems of immunogenicity of the recombinant enzymes used for therapy are presented.

Soluble expression, purification, and characterization of active recombinant human tissue plasminogen activator by auto-induction in E. coli

Background

Human tissue plasminogen activator (tPA) belongs to the serine protease family. It converts plasminogen into plasmin and is used clinically to treat thrombosis. Human tPA is composed of 527 amino acids residues and contains 17 disulfide bonds. Escherichia coli has been used only rarely for the efficient production of recombinant tPA. However, the functional expression of full-length tPA that contains multiple disulfide bonds on an industrial scale remains challenging. Here, we describe the soluble expression and characterization of full-length tPA by auto-induction in E. coli.

Results

We achieved optimal levels of gene expression, minimized negative effects related to the production of heterologous proteins, and optimized cytoplasmic yields. Three different E. coli strains, BL21 (DE3), Rosetta, and Origami 2, could express tPA using an auto-induction mechanism. In addition, similar yields of recombinant protein were produced at temperatures of 33, 35, and 37°C. The E. coli strain origami 2 could increase disulfide bond formation in cytoplasmic tPA and produce purified soluble recombinant protein (~0.9 mg/l medium). The full-length tPA was monomeric in solution, and fibrin plate assays confirmed that the recombinant tPA displayed serine protease activity.

Conclusions

This is the first report that describes the heterologous expression of correctly folded active full-length tPA. This could provide valuable information for using prokaryotic auto-induction expression systems to produce tPA at industrial and pharmaceutical levels without in vitro refolding during the production step.

Proteomic study of the brackish water mussel Mytilopsis leucophaeata

BACKGROUND

We encountered the opportunity to study proteochemically a brackish water invertebrate animal, Mytilopsis leucophaeata, belonging to the bivalves which stem from the second half of the Cambrian Period (about 510 million years ago). This way, we were able to compare it with the vertebrate animal, the frilled shark (Chlamydoselachus anguineus) that stems from a much later period of geologic time (Permian: 245-286 MYA).

RESULTS

The mussel contains a well-adapted system of protein synthesis on the ER, protein folding on the ER, protein trafficking via COPI or clathrin-coated vesicles from endoplasmic reticulum (ER) to Golgi and plasmalemma, an equally well-developed system of actin filaments that with myosin forms the transport system for vesicular proteins and tubulin, which is also involved in ATP-driven vesicular protein transport via microtubules or transport of chromosomes in mitosis and meiosis. A few of the systems that we could not detect in M. leucophaeata in comparison with C. anguineus are the synaptic vesicle cycle components as synaptobrevin, cellubrevin (v-snare) and synaptosomal associated protein 25-A (t-snare), although one component: Ras-related protein (O-Rab1) could be involved in synaptic vesicle traffic. Another component that we did not find in M. leucophaeata was Rab11 that is involved in the tubulovesicular recycling process of H+/K+-ATPase in C. anguineus. We have not been able to trace the H+/K+-ATPase of M. leucophaeata, but Na+/K+-ATPase was present. Furthermore, we have studied the increase of percent protein expression between 1,070 MYA (the generation of the Amoeba Dictyostelium discoideum) and present (the generation of the mammal Sus scrofa = wild boar). In this time span, three proteomic uprises did occur: 600 to 500 MYA, 47.5 to 4.75 MYA, and 1.4 to 0 MYA. The first uprise covers the generation of bivalves, the second covers gold fish, chicken, brine shrimp, house mouse, rabbit, Japanese medaka and Rattus norvegicus, and the third covers cow, chimpanzee, Homo sapiens, dog, goat, Puccinia graminis and wild boar. We hypothesise that the latter two uprises are related to geological and climate changes and their compensation in protein function expression.

CONCLUSIONS

The proteomic and evolutionary data demonstrate that M. leucophaeata is a highly educatioanal animal to study.

Comparison of the cytoplasmic and periplasmic production of reteplase in Escherichia coli

Reteplase is the recombinant type of tissue plasminogen activator variant. In this study, preplasmic and cytoplasmic (as inclusion body: IBs) production and activity of recombinant reteplase in E. coli were investigated and compared using a pET system (pET22b and pET15b). The cDNA of reteplase was cloned by polymerase chain reaction (PCR) amplification, sequenced, inserted into the vector pET 22b and pET15b, and expressed using isopropyl β-D-1-thiogalactopyranoside (IPTG). The recombinant plasmid was expressed in the form of inclusion body in pET 15b and in periplasmic space in pET22b. The obtained results of inclusion body extraction from recombinant pET22b (rpET22b) and recombinant pET15b (rpET15b) plasmids using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed a band of ~39 kD. However, the obtained results of periplasmic space extraction from rpET22b plasmid showed a very weak band, while cytoplasmic expression of reteplase (pET15b) produced a strong protein band confirmed with Western blotting. Consequently, our results demonstrated that the cytoplasmic expression system is efficient for the production of reteplase protein in prokaryote systems and a high amount of reteplase was obtained from the expressed proteins in the form of IBs. The obtained activity of rpET15b plasmid showed a higher enzyme absorbance in comparison to rpET22b plasmid. This suggests rpET15b as an appropriate candidate for reteplase production.

Expression and large-scale production of human tissue plasminogen activator (t-PA) in transgenic tobacco plants using different signal peptides

An attempt was made to assess the expression level and targeting of a human protein entitled recombinant tissue plasminogen activator (rt-PA) through accumulation in three cellular compartments including the endoplasmic reticulum and cytosolic and apoplastic spaces in transgenic tobacco plants. In this context, three chimeric constructs pBI-SP-tPA, pBI-tPA-KDEL, and pBI-Ext-tPA were employed and transferred into the tobacco plants through a popular transformation-based system called Agrobacterium tumefaciens. As an initial screening system, the incorporation of the rt-PA gene in the genomic DNA of tobacco transgenic plants and the possible existence of the rt-PA-specific transcript in the total RNAs of transgenic plant leaves were confirmed via PCR and reverse transcription (RT)-PCR, respectively. Southern blot analysis, in addition, was used to determine the copy number of the corresponding gene (i.e., t-PA) transformed into the each transgenic plant; one or more copies were detected regarding transformants derived from all three abovementioned constructs. According to the enzyme-linked immunosorbent assay, the mean values of t-PA expression were calculated as 0.50, 0.68, and 0.69 μg/mg of the total soluble protein when a collection containing 30 transgenic plants transformed with pBI-SP-tPA, pBI-tPA-KDEL, and pBI-Ext-tPA was taken into account, respectively. The zymography assay was lastly performed and concluded the expression of the properly folded rt-PA in this expression system. Our results, altogether, revealed that tobacco plants could be utilized as a bioreactor system for the large-scale production of enzymatically active t-PA and presumably other therapeutic recombinant proteins in large quantities.

Expression of the recombinant plasminogen activator (reteplase) by a non-lytic insect cell expression system

Reteplase is a potent thrombolytic agent which is widely used in the management of acute myocardial infarction and stroke. It belongs to the third generation of the thrombolytic drugs and has been derived from native human tissue plasminogen activator by removing three domains of it and keeping the Kringle 2 and Serine protease domains. However, the high cost of this drug, has limited the application of this drug especially in the developing and third world countries. The most laborious steps in the bacterial production of this drug is its purification and refolding steps which keep the process yield low and the cost high. Therefore, in the present study we evaluated the expression of reteplase by a non-lytic insect cell expression system. Following cloning and transfection procedures, recombinant Sf9 insect cell clones expressing the reteplase protein were selected. Primarily, the expression was verified by dot-blot analysis and subsequently it was confirmed by Western Blotting showing a band of about 45 kD on nitrocellulose membrane. The biological activity of the expressed protein was also evaluated and showed to be about 29 IU/ml. This confirmed the possibility of expression and the correct folding of the expressed protein. Hence, optimization of the expression followed by purification of the protein could be the next steps of the study.

Cloning and Expression of Functional Reteplase in Escherichia coli TOP10

BACKGROUND

Production of tissue Plasminogen Activator protein (t-PA) in prokaryotes systems has many problems such as the lack of active protein production, multiple purification steps, and renaturation process which has been shown to be costly and time-consuming.

METHODS

In this study, reteplase which is the nonglycosylated active domain of t-PA was used to transform TOP10 Escherichia coli (E. coli) bacteria to resolve some of the above mentioned problems. Reteplase cDNA was ligated into pBAD/gIII plasmid which allowed secretion of this protein into the periplasmic space and would allow the correct formation of disulfide bonds in protein structure. The presence of reteplase cDNA in pBAD/gIII plasmid was confirmed by restriction digestion and sequencing. After induction of the expression of this protein by adding 0.0002% L-Arabinose to the medium, the proteins in periplasmic space as well as the inclusion bodies formed inside the cell were extracted. Subsequently, these proteins were purified and detected by Western blot method.

RESULTS

Our results showed that the amount of reteplase extracted from periplasmic space was much lower than the extracted inclusion bodies and large quantities of the recombinant protein were present as inclusion bodies. Therefore, it was more efficient to use inclusion body extraction method for protein isolation and purification.

CONCLUSION

We produced active reteplase after its expression in E. coli TOP10 and isolation of inclusion bodies produced the best results for purification and extraction of this protein.

Soluble expression of active recombinant human tissue plasminogen activator derivative (K2S) in Escherichia coli

CONTEXT

The kringle 2 plus serine protease domains (K2S) of human tissue plasminogen activator (tPA) is an efficacious thrombolytic drug, which has been used to treat heart attacks and strokes by breaking up the clots that cause them. It has nine disulfide bridges, which are needed for proper folding and be the bottleneck in improving the production in the Escherichia coli system. So far, few reports have described the production of soluble active K2S from E. coli.

OBJECTIVE

To achieve high-level expression of active K2S in the E. coli system.

MATERIALS AND METHODS

The DNA fragment coding for K2S was fused with the E. coli disulfide isomerase DsbC. The constructed fusion protein was expressed in E. coli, and then purified with the Ni(2+)-chelating affinity chromatography. K2S was released by cleavage with Factor Xa protease, and the thrombolytic activity was determined using the fibrin plate assay.

RESULTS

The fusion protein DsbC-K2S was found in the culture supernatant of recombinant E. coli as a soluble form of ~40%. The result of fibrinolysis fibrin plate assay showed that the purified recombinant K2S exhibited significant fibrinolysis activity in vitro.

DISCUSSION AND CONCLUSION

These works provided a novel approach for the production of active K2S in E. coli without the requirements of in vitro refolding process, and might establish a significant foundation for the following production of K2S.

Expression of a novel chimeric truncated t-PA in CHO cells based on in silico experiments

Tissue plasminogen activator (t-PA) is one of the fibrin-specific serine proteases that play a crucial role in the fibrinolytic system. The rapid clearance of the drug from the circulation, caused by its active uptake in the liver, has lead to complicated clinical applications. Different forms of plasminogen activators have been developed to treat thrombotic disease. Deletion of the first three domains of t-PA by gene manipulation techniques has shown a significant increase in its plasma half life. In order to compensate the disadvantage of higher bleeding risk, a novel chimeric truncated form of t-PA with 394 amino acids and more fibrin affinity compared to the truncated form was designed to be expressed in Chinese Hamster Ovarian (CHO) cells. The recombinant chimeric plasminogen activator consists of kringle 2 and serine protease (K2S) domains of t-PA, namely GHRP-SYQ-K2S. The level of expression was found to be 752 IU/ml with 566,917 IU/mg specific activity, based on amidolytic activity. The fibrin binding of this novel chimeric truncated t-PA was 86% of the full length t-PA at a fibrinogen concentration of 0.2 mg/ml. This could be a promising approach with more desirable pharmacodynamic properties compared to existing commercial forms.

Expression of active recombinant human tissue-type plasminogen activator by using in vivo polyhydroxybutyrate granule display

Recombinant human tissue plasminogen activator (rPA) is a truncated version of tissue plasminogen activator (tPA), which contains nine disulfide bonds and is prone to forming inactive inclusion bodies when expressed in bacteria. To obtain functional rPA expression, we displayed the rPA on the surface of polyhydroxybutyrate (PHB) granules using phasin as the affinity tag. rPA was fused to the N terminus of the phasin protein with a thrombin cleavage site as the linker. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblot analysis showed that rPA fusion was successfully displayed on the surface of PHB granules. An activity assay indicated that the rPA fusion is active. The in vivo surface display strategy for functional rPA expression in Escherichia coli is distinct for its efficient folding and easier purification and may be expanded to the expression of other eukaryotic proteins with complex conformation.

Asn and asn: critical residues for in vitro biological activity of reteplase

Reteplase (rPA) is a thrombolytic agent used for the treatment of acute myocardial infarction. We studied the expression of rPA and its selected asparagine mutants after integration into the Pichia genome. Though methanol induction of the native and the rPA mutants showed similar expression levels (~200–250 mg/L), the mutants displayed significant loss of protease activity. Strikingly, the clot lysis activities of these mutants were considerably different. While mutation of Asn¹² (N12P) of the Kringle 2 domain showed delayed clot lysis activity (t_1/2 = 38 min) compared to the native rPA (t_1/2 = 33 min), a faster rate of clot lysis (t_1/2 = 27 min) was observed when the Asn²⁷⁸ (N278S) of the serine protease domain was mutated. Interestingly, the slowest clot lysis activity (t_1/2 = 49 min) demonstrated by the double mutant (N12P, N278S) suggests the dominant role of Asn¹² in regulating the fibrinolytic activity of rPA. The results presented in this paper indicate that the fibrinolytic and the proteolytic activities of rPA are independent of each other.

Blockade of CD28 by a synthetical peptoid inhibits T-cell proliferation and attenuates graft-versus-host disease

CD28 is one of the costimulatory molecules crucial for T-cell activation and thus has become an attractive target for therapeutic immunomodulation. Conventional strategies for blocking CD28 activity using monoclonal antibodies, Fab fragments, antagonistic peptide and fusion proteins, have apparent disadvantages such as inherent immunogenicity, unwanted Fc signaling, poor tissue penetration and bioinstability. Recent research has been directed toward the creation of non-natural, sequence-specific biomimetic oligomers with bioinspired structures that capture the amino-acid interface of the targeted proteins. One such family of molecules is the poly-N-substituted glycines or peptoids, which have close structural similarity to peptides but are essentially invulnerable to protease degradation. To screen for peptoids that specifically target CD28, we first designed and chemically synthesized 19 candidate peptoids based on molecular modeling and docking. Using the phage-displaying system that expresses the extracellular domain of the CD28 homodimer and contains the core B7-binding motif, a peptoid (No. 9) with a molecular formula of C(21)H(29)N(3)O(7), was identified to display the highest binding activity to CD28. This peptoid not only inhibited the lymphocyte proliferation in vitro, but suppressed immunoresponses against alloantigens in vivo, and attenuated the graft-versus-host disease in a mouse bone-marrow transplantation model. These results suggested that peptoids targeting CD28 are effective agents for blocking the CD28-mediated costimulation and suitable for development of novel therapeutic approaches for diseases involving this pathway.

Cloning and expression of a human tissue plasminogen activator variant: K2S in Escherichia coli

The DNA sequence of Kringle-2 and serine protease domains of the human tissue plasminogen activator (reteplase, K2S) was PCR amplified. This product was then cloned into the expression vector pET15b plasmid. The presence of the insert was confirmed by restriction digestion, PCR and determination of the nucleotide sequence. By using isopropyl beta-D thiogalactopyranoside (IPTG), reteplase was induced in E. coli BL21 cells and analyzed using polyacrylamide gel electrophoresis (PAGE).

A comparative investigation on different refolding strategies of recombinant human tissue-type plasminogen activator derivative

Recombinant human tissue-type plasminogen activator derivative (r-PA), fused with thioredoxin (Trx), was expressed in Escherichia coli. The resultant fusion protein, Trx-r-PA, was almost completely in the form of inclusion bodies and without activity. Different refolding strategies were investigated including different post-treatment of solubilized Trx-r-PA inclusion bodies, on-column refolding by size-exclusion chromatography (SEC) using three gel types (Sephacryl S-200, S-300 and S-400), refolding by Sephacryl S-200 with a urea gradient and two-stage temperature control in refolding. An optimized on-column refolding process for Trx-r-PA inclusion bodies was established. The collected Trx-r-PA inclusion bodies were dissolved in 6 M: guanidine hydrochloride (Gdm.HCl), and the denatured protein was separated from dithiothreitol (DTT) and Gdm.HCl with a G25 column and simultaneously dissolved in 8 M: urea containing oxidized glutathione (GSSG). Finally a refolding of Trx-r-PA protein on Sephacryl S-200 column with a decreasing urea gradient combined with two-stage temperature control was employed, and the activity recovery of refolded protein was increased from 3.6 to 13.8% in comparison with the usual dilution refolding.

Extracellular production of Streptomyces lividans acetyl xylan esterase A in Escherichia coli for rapid detection of activity

Acetyl xylan esterase A (AxeA) from Streptomyces lividans belongs to a large family of industrially relevant polysaccharide esterases. AxeA and its truncated form containing only the catalytically competent domain, AxeA(tr), catalyze both the deacetylation of xylan and the N-deacetylation of chitosan. This broad substrate specificity lends additional interest to their characterization and production. Here, we report three systems for extracellular production of AxeA(tr): secretion from the native host S. lividans with the native signal peptide, extracellular production in Escherichia coli with the native signal peptide, and in E. coli with the OmpA signal peptide. Over five to seven days of a shake flask culture, the native host S. lividans with the native signal peptide secreted AxeA(tr) into the extracellular medium in high yield (388 mg/L) with specific activity of 19 U/mg corresponding to a total of 7000 U/L. Over one day of shake flask culture, E. coli with the native secretion signal peptide produced 84-fold less in the extracellular medium (4.6 mg/L), but the specific activity was higher (100 U/mg) corresponding to a total of 460 U/L. A similar E. coli culture using the OmpA signal peptide, produced 10mg/L with a specific activity of 68 U/mg, corresponding to a total of 680 U/L. In 96-well microtiter plates, extracellular production with E. coli gave approximately 30 and approximately 86 microg/mL in S. lividans. Expression in S. lividans with the native signal peptide is best for high level production, while expression in E. coli using the OmpA secretion signal peptide is best for high-throughput expression and screening of variants in microtiter plate format.

Twin-arginine signal peptide attributes effective display of CD147 to filamentous phage

A novel phagemid (pTat8) was constructed in this study to improve the quality of a molecule displayed on filamentous phage. The twin-arginine translocation (Tat) pathway was chosen for transporting and integrating a CD147 molecule into a phage particle via gpVIII. The parent vector pComb8-CD147Ex was modified by substituting a Sec signal sequence (PelB) with a twin-arginine signal sequence from trimethylamine N-oxide reductase (TorA). The characteristics of the CD147 displayed on the phage particle were evaluated by Sandwich ELISA and Western immunoblotting. A Tat-dependent leader was found to be superior to the Sec leader for the phage display of CD147. Our findings further support the involvement of an Escherichia coli Tat translocase in mediating the integration of a hydrophobic transmembrane protein into the inner membrane. This modified phagemid will be useful in phage display technique when the correctly folded structure is required (i.e., antibody libraries and ligand-receptor tracing).

Recombinant protein secretion in Escherichia coli

The secretory production of recombinant proteins by the Gram-negative bacterium Escherichia coli has several advantages over intracellular production as inclusion bodies. In most cases, targeting protein to the periplasmic space or to the culture medium facilitates downstream processing, folding, and in vivo stability, enabling the production of soluble and biologically active proteins at a reduced process cost. This review presents several strategies that can be used for recombinant protein secretion in E. coli and discusses their advantages and limitations depending on the characteristics of the target protein to be produced.

Strategies for the recovery of active proteins through refolding of bacterial inclusion body proteins

Recent advances in generating active proteins through refolding of bacterial inclusion body proteins are summarized in conjunction with a short overview on inclusion body isolation and solubilization procedures. In particular, the pros and cons of well-established robust refolding techniques such as direct dilution as well as less common ones such as diafiltration or chromatographic processes including size exclusion chromatography, matrix- or affinity-based techniques and hydrophobic interaction chromatography are discussed. Moreover, the effect of physical variables (temperature and pressure) as well as the presence of buffer additives on the refolding process is elucidated. In particular, the impact of protein stabilizing or destabilizing low- and high-molecular weight additives as well as micellar and liposomal systems on protein refolding is illustrated. Also, techniques mimicking the principles encountered during in vivo folding such as processes based on natural and artificial chaperones and propeptide-assisted protein refolding are presented. Moreover, the special requirements for the generation of disulfide bonded proteins and the specific problems and solutions, which arise during process integration are discussed. Finally, the different strategies are examined regarding their applicability for large-scale production processes or high-throughput screening procedures.

Displaying and epitope mapping of CD147 on VCSM13 phages: influence of Escherichia coli strains

The external domain of a human leukocyte surface molecule, CD147 was displayed on the surface of phage. Two Escherichia coli laboratory strains, XL-1 Blue and TG-1, were chosen to separately propagate the recombinant phages. By sandwich enzyme linked immunosorbent assay (ELISA), CD147 on phage particles were individually captured by six CD147 mAbs and subsequently detected by anti-M13 conjugated HRP. All mAbs specifically bound the CD147 on phage particles derived from TG-1. On the contrary, only four of them could recognize the CD147 on phages produced by XL-1 Blue. The results indicate that the environment in the TG-1 periplasm is more appropriate than that of XL-1 Blue for promoting the suitable folding of CD147. This finding emphasizes the importance of selecting the appropriate E. coli host for display of a complex protein. The epitopes of CD147 displayed on the phage were further mapped by competitive inhibition ELISA, which is a reliable and economical method. Certain clusters of mAb recognition areas were identified and will provide valuable information for the discovery of the ligand for CD147.