Development of an aqueous two-phase partitioning system for fractionating therapeutic proteins from tobacco extract

Integrating plant molecular farming and materials research for next-generation vaccines

Biologics - medications derived from a biological source - are increasingly used as pharmaceuticals, for example, as vaccines. Biologics are usually produced in bacterial, mammalian or insect cells. Alternatively, plant molecular farming, that is, the manufacture of biologics in plant cells, transgenic plants and algae, offers a cheaper and easily adaptable strategy for the production of biologics, in particular, in low-resource settings. In this Review, we discuss current vaccination challenges, such as cold chain requirements, and highlight how plant molecular farming in combination with advanced materials can be applied to address these challenges. The production of plant viruses and virus-based nanotechnologies in plants enables low-cost and regional fabrication of thermostable vaccines. We also highlight key new vaccine delivery technologies, including microneedle patches and material platforms for intranasal and oral delivery. Finally, we provide an outlook of future possibilities for plant molecular farming of next-generation vaccines and biologics.

Integrating plant molecular farming and materials research for next-generation vaccines

Biologics - medications derived from a biological source - are increasingly used as pharmaceuticals, for example, as vaccines. Biologics are usually produced in bacterial, mammalian or insect cells. Alternatively, plant molecular farming, that is, the manufacture of biologics in plant cells, transgenic plants and algae, offers a cheaper and easily adaptable strategy for the production of biologics, in particular, in low-resource settings. In this Review, we discuss current vaccination challenges, such as cold chain requirements, and highlight how plant molecular farming in combination with advanced materials can be applied to address these challenges. The production of plant viruses and virus-based nanotechnologies in plants enables low-cost and regional fabrication of thermostable vaccines. We also highlight key new vaccine delivery technologies, including microneedle patches and material platforms for intranasal and oral delivery. Finally, we provide an outlook of future possibilities for plant molecular farming of next-generation vaccines and biologics.

Initial Screening of Poly(ethylene glycol) Amino Ligands for Affinity Purification of Plasmid DNA in Aqueous Two-Phase Systems

Gene therapy and DNA vaccination are among the most expected biotechnological and medical advances for the coming years. However, the lack of cost-effective large-scale production and purification of pharmaceutical-grade plasmid DNA (pDNA) still hampers their wide application. Downstream processing, which is mainly chromatography-based, of pDNA remains the key manufacturing step. Despite its high resolution, the scaling-up of chromatography is usually difficult and presents low capacity, resulting in low yields. Alternative methods that are based on aqueous two-phase systems (ATPSs) have been studied. Although higher yields may be obtained, its selectivity is often low. In this work, modified polymers based on poly(ethylene glycol) (PEG) derivatisation with amino groups (PEG–amine) or conjugation with positively charged amino acids (PEG–lysine, PEG–arginine, and PEG–histidine) were studied to increase the selectivity of PEG–dextran systems towards the partition of a model plasmid. A two-step strategy was employed to obtain suitable pure formulations of pDNA. In the first step, a PEG–dextran system with the addition of the affinity ligand was used with the recovery of the pDNA in the PEG-rich phase. Then, the pDNA was re-extracted to an ammonium-sulphate-rich phase in the second step. After removing the salt, this method yielded a purified preparation of pDNA without RNA and protein contamination.

A combined pH and temperature precipitation step facilitates the purification of tobacco-derived recombinant proteins that are sensitive to extremes of either parameter

Incubation at pH 4.0 or blanching at ∼65°C facilitates the purification of biopharmaceutical proteins from plants by precipitating most of the host cell proteins (HCPs) before chromatography. However, both methods are compatible only with pH or thermostable target proteins whereas many target proteins may irreversibly denature, e.g., at pH < 4.0. Here, we developed a combined pH/temperature treatment for clarified tobacco extracts and intact leaves. The latter were subjected to a blanching procedure, i.e., the submersion into a hot buffer. Using a design of experiments approach we identified conditions that remove ∼70% of HCPs at ∼55°C, using the thermosensitive antibody 2G12 and the pH-sensitive DsRed as model proteins. We found that pH and temperature exerted a combined effect during the precipitation of HCPs in the pH range 5.0-7.0 at 35°C-60°C. For clarified extracts, the temperature required to achieve a DsRed purity threshold of 20% total soluble protein (TSP) increased from 54°C to 63°C when the pH was increased from 6.4 to 7.3. The pH-stable antibody 2G12 was less responsive to the combined treatment, but the purity of 1% TSP was achieved at 35°C instead of 44°C when the pH was reduced from 6.3 to 5.8. When blanching intact leaves, product losses were not exacerbated at pH 4.0. Indeed, the highest DsRed purity (58% TSP) was achieved at this pH, combined with a temperature of 60°C and an incubation time of 30 min. In contrast, the highest 2G12 purity (0.7% TSP) was achieved at pH 5.1 and 40°C with an incubation time of 20 min. Our data suggest that a combined pH/temperature regime can avoid extreme values of either parameter; therefore, broadening the applicability of these simple purification techniques to other recombinant proteins.

Aqueous Two-Phase Systems for Cleanup and Recovery of Enzymes from Plants and Plant-Derived Extracts

The increasing interest of the biopharmaceutical industry to exploit plants as a commercially viable production system is demanding the development of new strategies to maximize product recovery. Aqueous two-phase systems (ATPSs) are a primary recovery technique that has shown great potential for the efficient extraction and purification of biological products, from organelles to proteins and low-molecular-weight compounds. The evaluation of different system parameters upon the partitioning behavior can provide the conditions that favor the concentration of contaminants and the desired target protein in opposite phases. The protocols described here provide the basic strategy to explore the use of ATPSs for the isolation and partial purification of native and recombinant proteins from plants and plant-derived extracts.

Extraction and purification methods in downstream processing of plant-based recombinant proteins

During the last two decades, the production of recombinant proteins in plant systems has been receiving increased attention. Currently, proteins are considered as the most important biopharmaceuticals. However, high costs and problems with scaling up the purification and isolation processes make the production of plant-based recombinant proteins a challenging task. This paper presents a summary of the information regarding the downstream processing in plant systems and provides a comprehensible overview of its key steps, such as extraction and purification. To highlight the recent progress, mainly new developments in the downstream technology have been chosen. Furthermore, besides most popular techniques, alternative methods have been described.

A Novel Aqueous Two Phase System Composed of Surfactant and Xylitol for the Purification of Lipase from Pumpkin (Cucurbita moschata) Seeds and Recycling of Phase Components

Lipase is one of the more important enzymes used in various industries such as the food, detergent, pharmaceutical, textile, and pulp and paper sectors. A novel aqueous two-phase system composed of surfactant and xylitol was employed for the first time to purify lipase from Cucurbita moschata. The influence of different parameters such as type and concentration of surfactants, and the composition of the surfactant/xylitol mixtures on the partitioning behavior and recovery of lipase was investigated. Moreover, the effect of system pH and crude load on the degree of purification and yield of the purified lipase were studied. The results indicated that the lipase was partitioned into the top surfactant rich phase while the impurities partitioned into the bottom xylitol-rich phase using an aqueous two phase system composed of 24% (w/w) Triton X-100 and 20% (w/w) xylitol, at 56.2% of tie line length (TLL), (TTL is one of the important parameters in this study and it is determined from a bimodal curve in which the tie-line connects two nodes on the bimodal, that represent concentration of phase components in the top and bottom phases) and a crude load of 25% (w/w) at pH 8.0. Recovery and recycling of components was also measured in each successive step process. The enzyme was successfully recovered by the proposed method with a high purification factor of 16.4 and yield of 97.4% while over 97% of the phase components were also recovered and recycled. This study demonstrated that the proposed novel aqueous two phase system method is more efficient and economical than the traditional aqueous two phase system method for the purification and recovery of the valuable enzyme lipase.

Multistage aqueous two-phase extraction of a monoclonal antibody from cell supernatant

This article presents results of continuous multistage aqueous two-phase extraction of an immunoglobulin G1 from cell supernatant in a mixer-settler unit. An aqueous two-phase system consisting of polyethylene glycol 2000, phosphate salt, and water was applied without and with sodium chloride (NaCl). Influences of different parameters such as throughput, phase ratio, and stage number on the extraction performance were analyzed. For systems without NaCl, the extraction was carried out as a washing step. An increase of stage number from one to five stages enabled to increase the immunoglobulin G1 purity from 11.8 to 32.6% at a yield of nearly 90%. Furthermore, a reduction of product phase volume due to a higher phase ratio led to an increase of purity from 20.8 to 29.6% in a three-stage countercurrent extraction. For experiments with NaCl moderate partitioning conditions were adjusted by adding 8 wt% NaCl. In that case, the extraction was carried out as a stripping step.

Aqueous two-phase system strategies for the recovery of proteins from plants

The increasing interest of the biopharmaceutical industry to exploit plants as a commercially viable production system is demanding the development of new strategies to maximize product recovery. Aqueous two-phase systems (ATPSs) are a primary recovery technique that has shown great potential for the efficient extraction and purification of biological products. The evaluation of different system parameters upon the partitioning behavior can provide the conditions that favor the concentration of contaminants and the desired target protein in opposite phases. The protocols described provide the basic strategy to explore the use of ATPS for the isolation and partial purification of native and recombinant proteins expressed in plants.

A downstream process allowing the efficient isolation of a recombinant amphiphilic protein from tobacco leaves

The 65-kDa isoform of human glutamic acid decarboxylase (hGAD65) is a major autoantigen in autoimmune diabetes. The heterologous production of hGAD65 for diagnostic and therapeutic applications is hampered by low upstream productivity and the absence of a robust and efficient downstream process for product isolation. A tobacco-based platform has been developed for the production of an enzymatically-inactive form of the protein (hGAD65mut), but standard downstream processing strategies for plant-derived recombinant proteins cannot be used in this case because the product is amphiphilic. We therefore evaluated different extraction buffers and an aqueous micellar two-phase system (AMTPS) to optimize the isolation and purification of hGAD65mut from plants. We identified the extraction conditions offering the greatest selectivity for hGAD65mut over native tobacco proteins using a complex experimental design approach. Under our optimized conditions, the most efficient initial extraction and partial purification strategy achieved an overall hGAD65mut yield of 92.5% with a purification factor of 12.3 and a concentration factor of 23.8. The process also removed a significant quantity of phenols, which are major contaminants present in tobacco tissue. This is the first report describing the use of AMTPS for the partial purification of an amphiphilic recombinant protein from plant tissues and our findings could also provide a working model for the initial recovery and partial purification of hydrophobic recombinant proteins from transgenic tobacco plants.

Downstream processing of biopharmaceutical proteins produced in plants: the pros and cons of flocculants

All biological platforms for the manufacture of biopharmaceutical proteins produce an initially turbid extract that must be clarified to avoid fouling sensitive media such as chromatography resins. Clarification is more challenging if the feed stream contains large amounts of dispersed particles, because these rapidly clog the filter media typically used to remove suspended solids. Charged polymers (flocculants) can increase the apparent size of the dispersed particles by aggregation, facilitating the separation of solids and liquids, and thus reducing process costs. However, many different factors can affect the behavior of flocculants, including the pH and conductivity of the medium, the size and charge distribution of the particulates, and the charge density and molecular mass of the polymer. Importantly, these properties can also affect the recovery of the target protein and the overall safety profile of the process. We therefore used a design of experiments approach to establish reliable predictive models that characterize the impact of flocculants during the downstream processing of biopharmaceutical proteins. We highlight strategies for the selection of flocculants during process optimization. These strategies will contribute to the quality by design aspects of process development and facilitate the development of safe and efficient downstream processes for plant-derived pharmaceutical proteins.

Process integration for the recovery and purification of recombinant Pseudomonas fluorescens proline dehydrogenase using aqueous two-phase systems

The integration of refolding, reconstitution and two-phase partitioning in aqueous two-phase systems (ATPS) which is composed of polyethylene glycol (PEG) and sodium carbonate (Na2CO3) was employed as a novel method for recovery and purification of recombinant Pseudomonas fluorescens proline dehydrogenase (ProDH). To obtain an optimal condition, the influence of different parameters, such as PEG molecular weight (MW), type and concentration of salt, pH, and NaCl addition on the partitioning features of target enzyme was also investigated. Combining the refolding, reconstitution and two-phase partitioning in an optimized ATPS of 14% (w/w) PEG-1000 and 12% (w/w) Na2CO3 at pH 8.0 resulted in a yield of 61.5%, purification factor of 27.0, recovery of 430.7% and specific activity of 600.0U/mg. The recombinant P. fluorescens enzyme was preferentially partitioned into the top PEG-rich phase. NaCl addition decreased greatly the partition coefficient and recovery of ProDH. In addition, the resulting protein pattern by SDS-PAGE demonstrated the adequacy of presented procedure for enzyme recovery. Overall, our data confirmed that the PEG-1000/Na2CO3 aqueous two-phase partitioning combined with refolding and reconstitution can be used as an efficient integrated process for recovery and purification of recombinant ProDH from inclusion bodies in only one step.

Purification of the therapeutic antibody trastuzumab from genetically modified plants using safflower Protein A-oleosin oilbody technology

Production of therapeutic monoclonal antibodies using genetically modified plants may provide low cost, high scalability and product safety; however, antibody purification from plants presents a challenge due to the large quantities of biomass that need to be processed. Protein A column chromatography is widely used in the pharmaceutical industry for antibody purification, but its application is limited by cost, scalability and column fouling problems when purifying plant-derived antibodies. Protein A-oleosin oilbodies (Protein A-OB), expressed in transgenic safflower seeds, are relatively inexpensive to produce and provide a new approach for the capture of monoclonal antibodies from plants. When Protein A-OB is mixed with crude extracts from plants engineered to express therapeutic antibodies, the Protein A-OB captures the antibody in the oilbody phase while impurities remain in the aqueous phase. This is followed by repeated partitioning of oilbody phase against an aqueous phase via centrifugation to remove impurities before purified antibody is eluted from the oilbodies. We have developed this purification process to recover trastuzumab, an anti-HER2 monoclonal antibody used for therapy against specific breast-cancers that over express HER2 (human epidermal growth factor receptor 2), from transiently infected Nicotiana benthamiana. Protein A-OB overcomes the fouling problem associated with traditional Protein A chromatography, allowing for the development of an inexpensive, scalable and novel high-resolution method for the capture of antibodies based on simple mixing and phase separation.

Process for purification of monoclonal antibody expressed in transgenic Lemna plant extract using dextran-coated charcoal and hexamer peptide affinity resin

The production of therapeutic proteins using transgenic plants offers several advantages, including low production cost, absence of human pathogens, presence of glycosylation mechanisms, and the ability to fold complex therapeutic proteins into their proper conformation. However, impurities such as phenolic compounds and pigments encountered during purification are quite different from those faced during purification from mammalian cell culture supernatants. This paper deals with the development of a pretreatment and affinity separation process for the purification of a monoclonal antibody from transgenic Lemna plant extract. A pretreatment step is described using dextran-coated charcoal for the removal of pigments and phenolic compounds without reducing the antibody concentration. Then, the peptide affinity ligand HWRGWV coupled to a commercial polymethacrylate resin is used for the capture and purification of MAb from the pretreated plant extract. The final yield and purity of the MAb obtained were 90% and 96% respectively. The performance of the hexamer peptide resin after the pretreatment step was found to be similar to that obtained with a commercial Protein A resin.

[Current status in the commercialization and application of genetically modified plants and their effects on human and livestock health and phytoremediation]

Developments in the use of genetically modified plants for human and livestock health and phytoremediation were surveyed using information retrieved from Entrez PubMed, Chemical Abstracts Service, Google, congress abstracts and proceedings of related scientific societies, scientific journals, etc. Information obtained was classified into 8 categories according to the research objective and the usage of the transgenic plants as 1: nutraceuticals (functional foods), 2: oral vaccines, 3: edible curatives, 4: vaccine antigens, 5: therapeutic antibodies, 6: curatives, 7: diagnostic agents and reagents, and 8: phytoremediation. In total, 405 cases were collected from 2006 to 2010. The numbers of cases were 120 for nutraceuticals, 65 for oral vaccines, 25 for edible curatives, 36 for vaccine antigens, 36 for therapeutic antibodies, 76 for curatives, 15 for diagnostic agents and reagents, and 40 for phytoremediation (sum of each cases was 413 because some reports were related to several categories). Nutraceuticals, oral vaccines and curatives were predominant. The most frequently used edible crop was rice (51 cases), and tomato (28 cases), lettuce (22 cases), potato (18 cases), corn (15 cases) followed.

Recent advances towards development and commercialization of plant cell culture processes for the synthesis of biomolecules

Plant cell culture systems were initially explored for use in commercial synthesis of several high-value secondary metabolites, allowing for sustainable production that was not limited by the low yields associated with natural harvest or the high cost associated with complex chemical synthesis. Although there have been some commercial successes, most notably paclitaxel production from Taxus sp., process limitations exist with regards to low product yields and inherent production variability. A variety of strategies are being developed to overcome these limitations including elicitation, in situ product removal and metabolic engineering with single genes and transcription factors. Recently, the plant cell culture production platform has been extended to pharmaceutically active heterologous proteins. Plant systems are beneficial because they are able to produce complex proteins that are properly glycosylated, folded and assembled without the risk of contamination by toxins that are associated with mammalian or microbial production systems. Additionally, plant cell culture isolates transgenic material from the environment, allows for more controllable conditions over field-grown crops and promotes secretion of proteins to the medium, reducing downstream purification costs. Despite these benefits, the increase in cost of heterologous protein synthesis in plant cell culture as opposed to field-grown crops is significant and therefore processes must be optimized with regard to maximizing secretion and enhancing protein stability in the cell culture media. This review discusses recent advancements in plant cell culture processing technology, focusing on progress towards overcoming the problems associated with commercialization of these production systems and highlighting recent commercial successes.

Application of electrochemically produced aluminum hydroxide gel for prepurification of recombinant synthetic green fluorescent protein produced in tobacco leaves

The use of recombinant proteins has increased greatly in recent years, as also have increased the number of techniques and materials used for their production and purification. Among the different types of bioreactors being studied, there is a general consensus among scientists that production in green plant tissues such as leaves is more feasible. However, the presence of chlorophyll and phenolic compounds in plant extracts, which can precipitate and denature the proteins besides damaging separation membranes and gels, makes this technology impracticable on a commercial scale. In the present work, the adsorption to electrochemically produced aluminum hydroxide gel was applied as a prepurification step for recombinant synthetic green fluorescent protein (sGFP), also referred to as enhanced green fluorescent protein, produced in Nicotiana benthamiana leaves. Removal efficiencies of 99.7% of chlorophyll, 88.5% of phenolic compounds, and 38.5% of native proteins from the N. benthamiana extracts were achieved without removing sGFP from the extracts. As electrochemical preparation of aluminum hydroxide gel is a cost-effective technique, its use can substantially contribute to the development of future production platforms for recombinant proteins produced in green plant tissues of pharmaceutical and industrial interest.

Recombinant protein expression in Nicotiana

Recombinant protein pharmaceuticals are now widely used in treatment of chronic diseases, and several recombinant protein subunit vaccines are approved for human and veterinary use. With growing demand for complex protein pharmaceuticals, such as monoclonal antibodies, manufacturing capacity is becoming limited. There is increasing need for safe, scalable, and economical alternatives to mammalian cell culture-based manufacturing systems, which require substantial capital investment for new manufacturing facilities. Since a seminal paper reporting immunoglobulin expression in transgenic plants was published in 1989, there have been many technological advances in plant expression systems to the present time where production of proteins in leaf tissues of nonfood crops such as Nicotiana species is considered a viable alternative. In particular, transient expression systems derived from recombinant plant viral vectors offer opportunities for rapid expression screening, construct optimization, and expression scale-up. Extraction of recombinant proteins from Nicotiana leaf tissues can be achieved by collection of secreted protein fractions, or from a total protein extract after grinding the leaves with buffer. After separation from solids, the major purification challenge is contamination with elements of the photosynthetic complex, which can be solved by application of a variety of facile and proven strategies. In conclusion, the technologies required for safe, efficient, scalable manufacture of recombinant proteins in Nicotiana leaf tissues have matured to the point where several products have already been tested in phase I clinical trials and will soon be followed by a rich pipeline of recombinant vaccines, microbicides, and therapeutic proteins.

Optimisation of the purification process of a tumour-targeting antibody produced in N. benthamiana using vacuum-agroinfiltration

It was previously demonstrated that the tumour-targeting antibody mAb H10 can be transiently expressed and purified at high levels in Nicotiana benthamiana by using a vacuum-agroinfiltration system boosted by the use of a virus silencing suppressor protein. Scope of this work was to analyse different steps of protein extraction from agroinfiltrated leaves to optimise the purification process of the secretory mAb H10 providing new insights in the field of large-scale plant production. Two different extraction procedures (mechanical shearing/homogenisation and recovery of intercellular fluids -IFs-) were evaluated and compared in terms of purified antibody yields, antibody degradation and total phenolic compounds content. Mechanical grinding from fresh leaf tissues gave the highest purification yield (75 mg/kg Fresh Weight -75% intact tetrameric IgG-) and total phenolics concentration in the range of 420 μg/g FW. The second extraction procedure, based on the recovery of IFs, gave purification yields of 15-20 mg/kg FW (corresponding to 27% of total soluble protein) in which about 40% of purified protein is constituted by fully assembled IgG with a total phenolic compounds content reduced by one order of magnitude (21 μg/g FW). Despite a higher antibody degradation, purification from intercellular fluids demonstrated to be very promising since extraction procedures resulted extremely fast and amenable to scaling-up. Overall data highlight that different extraction procedures can dramatically affect the proteolytic degradation and quality of antibody purified from agroinfiltrated N. benthamiana leaves. Based on these results, we optimised a pilot-scale purification protocol using a two-step purification procedure from batches of fresh agroinfiltrated leaves (250 g) allowing purification of milligram quantities (average yield 40 mg/kg FW) of fully assembled and functional IgG with a 99.4% purity, free of phenolic and alkaloid compounds with low endotoxin levels (<1 EU/ml).

Aqueous two-phase systems strategies for the recovery and characterization of biological products from plants

The increasing interest of the biopharmaceutical industry to exploit plants as economically viable production systems is demanding the development of new downstream strategies to maximize product recovery. Aqueous two-phase systems (ATPSs) are a primary recovery technique that has shown great potential for the efficient extraction and purification of biological compounds. The present paper gives an overview of the efficient use of ATPS-based strategies for the isolation and partial purification of bioparticles from plant origin. Selected examples highlight the main advantages of this technique, i.e. scaling-up feasibility, process integration capability and biocompatibility. An overview of the recent approach of coupling ATPSs with traditional techniques to increase bioseparation process performance is discussed. A novel approach to characterization protein from plants combining ATPSs and two-dimensional electrophoresis (2-DE) is introduced as a tool for process development. In the particular case of products from plant origin, early success has demonstrated the potential application of ATPS-based strategies to address the major disadvantages of the traditional recovery and purification techniques. This literature review discloses the relevant contribution of ATPSs to facilitate the establishment of bioprocesses in the growing field of high-value products from plants.

Recovery of nicotine-free proteins from tobacco leaves using phosphate buffer system under controlled conditions

Establishment of an effective, high-throughput processing system to recover protein from tobacco with no nicotine contamination is essential and vital to the development of value-added, alternative applications for tobacco farmers. We have successfully developed a mechanism capable of processing up to 60 kg of tobacco leaves per hour with phosphate buffer (Na(2)HPO(4)-KH(2)PO(4)) simultaneously added to stabilize the protein as the plant was being disintegrated. The optimal processing parameters were identified, including the ratio of buffer to leaf (BLR) at 4.75 (w/w), buffer pH 7.85, and buffer concentration 0.085 mol/L, achieving a maximum yield of soluble protein at 12.85 mg/g fresh leaf. Acetone at -20 degrees C was the most effective among all methods investigated to remove nicotine from protein; however, it also drastically reduced the recovery rate of protein (63.3%). Ultrafiltration was only able to remove about 50% of the residual nicotine, although the protein recovery rate was high (94.7%). The residual nicotine content inherent in the recovered protein was completely removed by rinsing the protein with 85% phosphoric acid at pH 3.5 for three times with a protein recovery of 94.5%. The pilot-scale operation provides a solid foundation for further scale-up to industrial production of nicotine-free tobacco protein that could bring added value to tobacco for nonsmoking applications.

Characterization of green-tissue protein extract from alfalfa (Medicago sativa) exploiting a 3-D technique

There is a growing interest of pharmaceutical companies for plant-based production systems. To facilitate the general acceptance of plants as bioreactors, the establishment of efficient downstream operations is critical. It has been proposed that a better understanding of the properties of the contaminant proteins can benefit downstream processing design and operation. The coupled application of 2-DE with aqueous two-phase partitioning has been suggested as a practical 3-D method to characterize potential contaminant proteins from plant extracts. The application of this novel 3-D approach to a complex protein extract from alfalfa (Medicago sativa) containing a model recombinant protein (human granulocyte colony stimulating factor (hG-CSF)) resulted in the quantification of 55 protein spots. The 3-D properties (M(r), pI, and K(p)) obtained for 17 proteins comprising 69% of the alfalfa proteins, allowed the proposal of a prefractionation step as well as the identification of the target molecule (rG-CSF) from bulk of alfalfa proteins. The information obtained from this experimental approach was useful for the identification of the potential contaminant proteins that will occur in alfalfa when this plant is used as a host for recombinant proteins. Additionally, this method will assist in the design of adequate purification strategies for recombinant proteins expressed in alfalfa green tissue.

Combinatorial de novo design and application of a biomimetic affinity ligand for the purification of human anti-HIV mAb 4E10 from transgenic tobacco

Monoclonal anti-HIV antibody 4E10 (mAb 4E10) is one of the most broadly neutralizing antibodies against HIV, directed against a specific epitope on envelope protein gp41. In the present study, a combinatorial de novo design approach was used for the development of a biomimetic ligand for the affinity purification of mAb 4E10 from tobacco transgenic extract in a single chromatographic step. The biomimetic ligand (4E10lig) was based on a L-Phe/beta-Ala bi-substituted 1,3,5-triazine (Trz) scaffold (beta-Ala-Trz-L-Phe, 4E10lig) which potentially mimics the more pronounced electrostatic and hydrophobic interactions of mAb 4E10-binding sequence determined by screening of a random peptide library. This library was comprised of Escherichia coli cells harboring a plasmid (pFlitrx) engineered to express a fusion protein containing random dodecapeptides that were inserted into the active loop of thioredoxin, which itself was inserted into the dispensable region of the flagellin gene. Adsorption equilibrium studies with this biomimetic ligand and mAb 4E10 determined a dissociation constant (K(D)) of 0.41 +/- 0.05 microM. Molecular modeling studies of the biomimetic ligand revealed that it can potentially occupy the same binding site as the natural binding core peptide epitope. The biomimetic affinity adsorbent was exploited in the development of a facile mAb 4E10 purification protocol, affording mAb 4E10 of high purity (approximately 95%) with good overall yield (60-80%). Analysis of the antibody preparation by SDS-PAGE, enzyme-linked immunosorbent assays (ELISA), and western blot showed that the mAb 4E10 was fully active and free of degraded variants, polyphenols, and alkaloids.

Purification of human antibodies from transgenic corn using aqueous two-phase systems

A recombinant human antibody expressed in corn was purified using aqueous two-phase extraction. The antibody was an immunoglobulin G fully unglycosylated. Using systems of different compositions and/or pHs in each of one or two partitioning stages followed by one more stage in which the antibody was precipitated at the liquid/liquid interface facilitated the removal of different impurities in each stage. The best system yields a product 72% pure (22-fold purification) with a yield of 49%. The optimum extraction was done in two partitioning stages followed by an interfacial precipitation stage using poly(ethylene)glycol/potassium phosphate systems. NaCl was added to the first stage to eliminate large molecular weight impurities. The pH in the first stage was kept at 6 but a pH of 8 was used in the second stage and in the precipitation stage.

Application of a PEG/salt aqueous two-phase partition system for the recovery of monoclonal antibodies from unclarified transgenic tobacco extract

Aqueous two-phase partition systems (ATPS) have been widely used for the separation of a large variety of biomolecules. In the present report, the application of a polyethylene glycol/phosphate (PEG/phosphate) ATPS for the separation of anti-HIV monoclonal antibodies 2G12 (mAb 2G12) and 4E10 (mAb 4E10) from unclarified transgenic tobacco crude extract was investigated. Optimal conditions that favor opposite phase partitioning of plant debris/mAb as well as high recovery and purification were found to be 13.1% w/w (PEG 1500), 12.5% w/w (phosphate) at pH 5 with a phase ratio of 1.3 and 8.25% w/w unclarified tobacco extract load. Under these conditions, mAb 2G12 and mAb 4E10 were partitioned at the bottom phosphate phase with 85 and 84% yield and 2.4- and 2.1-fold purification, respectively. The proposed ATPS was successfully integrated in an affinity-based purification protocol, using Protein A, yielding antibodies of high purity and yield. In this study, ATPS was shown to be suitable for initial protein recovery and partial purification of mAb from unclarified transgenic tobacco crude extract.

Recovery and Purification of Nicotine from Waste Tobacco by Aqueous Two-Phase System/Reverse Extraction

A two-step process has been developed for the purification of nicotine from waste tobacco using an aqueous two-phase system and solvent reverse extraction. The partitioning behavior of nicotine was investigated in an isopropyl alcohol/ (NH4)2SO4 aqueous two-phase system. The effects of the addition of salt, pH and temperature on the partitioning behavior of nicotine were studied. The recovery rate of nicotine was 96.1% with a purity of above 99% when optimal conditions were used [(NH4)2SO4 25%, pH 9, temperature 35°C, isopropyl alcohol 5 mL].