Modifying secretion and post-translational processing in insect cells

Baculovirus-Assisted Production of Bartonella bacilliformis Proteins: A Potential Strategy for Improving Serological Diagnosis of Carrion's Disease

Carrion's disease, caused by Bartonella bacilliformis, is a neglected tropical disease prevalent in the Andean region of South America. Without antimicrobial treatment, this disease has a mortality rate of up to 88% in infected patients. The most common method for diagnosing B. bacilliformis infection is serological testing. However, the current serological assays are limited in sensitivity and specificity, underscoring the need for the development of novel and more accurate diagnostic tools. Recombinant proteins have emerged as promising candidates to improve the serological diagnosis of Carrion's disease. So, we focused on evaluating the conditions for producing two previously predicted proteins of B. bacilliformis using the baculovirus-insect cell expression system, mainly the flashBAC ULTRA technology. We assessed various parameters to identify the conditions that yield the highest protein production, including cell lines, temperature, and hours post-infection (hpi). The results showed that the expression conditions for achieving the highest yields of the Prot_689 and Prot_504 proteins were obtained using High Five™ cells at 21 °C and harvesting at 120 hpi. Subsequently, the seroreactivity of recombinant proteins was evaluated using positive sera from patients diagnosed with Carrion's disease. These findings offer valuable insights into the production conditions of B. bacilliformis recombinant proteins using the baculovirus system, which could significantly contribute to developing more precise diagnostic tools for Carrion's disease. Therefore, this research provides implications for improving diagnostics and potentially developing therapeutic strategies.

A concise guide to choosing suitable gene expression systems for recombinant protein production

This overview guides both novices and experienced researchers facing challenging targets to select the most appropriate gene expression system for producing a particular protein. By answering four key questions, readers can determine the most suitable gene expression system following a decision scheme. This guide addresses the most commonly used and accessible systems and provides brief descriptions of the main gene expression systems' key characteristics to assist decision making. Additionally, information has been included for selected less frequently used "exotic" gene expression systems.

Impact of dual-baculovirus infection on the Sf9 insect cell transcriptome during rAAV production using single-cell RNA-seq

The insect cell-baculovirus expression vector system (IC-BEVS) has shown to be a powerful platform to produce complex biopharmaceutical products, such as recombinant proteins and virus-like particles. More recently, IC-BEVS has also been used as an alternative to produce recombinant adeno-associated virus (rAAV). However, little is known about the variability of insect cell populations and the potential effect of heterogeneity (e.g., stochastic infection process and differences in infection kinetics) on product titer and/or quality. In this study, transcriptomics analysis of Sf9 insect cells during the production of rAAV of serotype 2 (rAAV2) using a low multiplicity of infection, dual-baculovirus system was performed via single-cell RNA-sequencing (scRNA-seq). Before infection, the principal source of variability in Sf9 insect cells was associated with the cell cycle. Over the course of infection, an increase in transcriptional heterogeneity was detected, which was linked to the expression of baculovirus genes as well as to differences in rAAV transgenes (rep, cap and gfp) expression. Noteworthy, at 24 h post-infection, only 29.4% of cells enclosed all three necessary rAAV transgenes to produce packed rAAV2 particles, indicating limitations of the dual-baculovirus system. In addition, the trajectory analysis herein performed highlighted that biological processes such as protein folding, metabolic processes, translation, and stress response have been significantly altered upon infection. Overall, this work reports the first application of scRNA-seq to the IC-BEVS and highlights significant variations in individual cells within the population, providing insight into the rational cell and process engineering toward improved rAAV2 production in IC-BEVS.

Comprehensive N- and O-Glycoproteomic Analysis of Multiple Chinese Hamster Ovary Host Cell Lines

Glycoproteomic analysis of three Chinese hamster ovary (CHO) suspension host cell lines (CHO-K1, CHO-S, and CHO-Pro5) commonly utilized in biopharmaceutical settings for recombinant protein production is reported. Intracellular and secreted glycoproteins were examined. We utilized an immobilization and chemoenzymatic strategy in our analysis. Glycoproteins or glycopeptides were first immobilized through reductive amination, and the sialyl moieties were amidated for protection. The desired N- or O-glycans and glycopeptides were released from the immobilization resin by enzymatic or chemical digestion. Glycopeptides were studied by Orbitrap Liquid chromatography-mass spectrometry (LC/MS), and the released glycans were analyzed by Matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF). Differences were detected in the relative abundances of N- and O-glycopeptide types, their resident and released glycans, and their glycoprotein complexity. Ontogeny analysis revealed key differences in features, such as general metabolic and biosynthetic pathways, including glycosylation systems, as well as distributions in cellular compartments. Host cell lines and subfraction differences were observed in both N- and O-glycan and glycoprotein pools. Differences were observed in sialyl and fucosyl glycan distributions. Key differences were also observed among glycoproteins that are problematic contaminants in recombinant antibody production. The differences revealed in this study should inform the choice of cell lines best suited for a particular bioproduction application.

Dot-Blotting: A Quick Method for Expression Analysis of Recombinant Proteins

Expressing recombinant proteins in heterologous host cells is a prerequisite for purification and other downstream processes. Cell cultures require a protein expression test to optimize incubation time, temperature, and additives (like chemical inducers) to identify the best growth conditions with maximum recombinant protein yield. However, running SDS-PAGE followed by western blotting is cumbersome and results are not quick. Here, I describe a simple protocol to quickly check the presence of recombinant protein in cell cultures using a dot-blot experiment. The cells can be rapidly lysed and directly spotted on the nitrocellulose membrane. Then, the membrane is incubated with a horseradish peroxidase (HRP) conjugated antibody raised against the affinity tag present on the recombinant protein to confirm the protein expression by chemiluminescence. It takes less than an hour to get results. This method rapidly investigates recombinant protein expression in different cell lines and tests other variables. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Protein expression analysis for eukaryotic systems Basic Protocol 2: Protein expression analysis for bacterial systems.

Immune Response in Mice Immunized with Chimeric H1 Antigens

Identification of a universal influenza vaccine candidate has remained a global challenge for both humans and animals. This study describes an approach that uses consensus sequence building to generate chimeric HAs (cHAs): two resultant H1 HA-based chimeras comprising of conserved sequences (within several areas spanning the head and stalk regions) of H1 and H5 or H9 HAs. These cHAs expressed in Drosophila cells (S2) were used to immunize mice. All immunized mice were protected from an infectious H1 virus challenge. Seroconverted mice sera to the H1 cHAs inhibited both the challenge virus and an H5 virus isolate by haemagglutination inhibition (HI) assay. These findings further emphasize that cHAs induce cross-reactive antibodies against conserved areas of both head and stalk regions of the seasonal influenza A (H1N1) pdm09 virus' HA and holds potential for further development of a universal influenza vaccine.

Insect High FiveTM cell line development using site-specific flipase recombination technology

Insect Trichoplusia ni High FiveTM (Hi5) cells have been widely explored for production of heterologous proteins, traditionally mostly using the lytic baculovirus expression vector system (BEVS), and more recently using virus-free transient gene expression systems. Stable expression in such host cells would circumvent the drawbacks associated with both systems when it comes to scale-up and implementation of more efficient high-cell density process modes for the manufacturing of biologics. In this work, we combined Flipase (Flp) recombinase-mediated cassette exchange (RMCE) with fluorescence-activated cell sorting (FACS) for generating a stable master clonal Hi5 cell line with the flexibility to express single or multiple proteins of interest from a tagged genomic locus. The 3-step protocol herein implemented consisted of (i) introducing the RMCE docking cassette into the cell genome by random integration followed by selection in Hygromycin B and FACS (Hi5-tagging population), (ii) eliminating cells tagged in loci with low recombination efficiency by transfecting the tagging population with an eGFP-containing target cassette followed by selection in G418 and FACS (Hi5-RMCE population), and (iii) isolation of pure eGFP-expressing cells by FACS and expansion to suspension cultures (Hi5-RMCE master clone). Exchangeability of the locus in the master clone was demonstrated in small-scale suspension cultures by replacing the target cassette by one containing a single protein (i.e. iCherry, as an intracellular protein model) or two proteins (i.e. influenza HA and M1 for virus-like particles production, as an extracellular protein model). Overall, the stable insect Hi5 cell platform herein assembled has the potential to assist and accelerate biologics development.

Recombinant Baculovirus-Produced Grass Carp Reovirus Virus-Like Particles as Vaccine Candidate That Provides Protective Immunity against GCRV Genotype II Infection in Grass Carp

Grass carp reovirus (GCRV) leads to severe hemorrhagic disease in grass carp (Ctenopharyngodon idella) and causes economic losses in grass carp aquaculture. Recent epidemiological investigations showed that GCRV genotype II is the dominant subtype in China. Therefore, it is very important to develop a novel vaccine for preventing diseases caused by GCRV genotype II. In this study, we employed a bac-to-bac expression system to generate GCRV-II-based virus-like particles (VLPs). Previous studies have shown that the structural proteins VP3, VP4, and VP38 encoded by the segments S3, S6, and S10 of type II GCRV are immunogenic. Hence, the GCRV-VLPs were produced by co-infection of sf9 cells with recombinant baculoviruses PFBH-VP3, PFBH-VP4, and PFBH-VP38. The expressions of VP3, VP4, and VP38 proteins in GCRV-VLPs were tested by IFA and Western blot analysis. By electron microscopic observations of ultrathin sections, purified VLPs showed that the expressed proteins are similar in shape to GCRV genotype II with a size range from 40 nm to 60 nm. The immunogenicity of GCRV-VLPs was evaluated by the injection immunization of grass carp. The analysis of serum-specific IgM antibody showed that grass carp immunized with GCRV-VLPs produced GCRV-specific antibodies. Furthermore, injection with GCRV-VLPs increased the expressions of immune-related genes (IgM, IFN, TLR3, TLR7) in the spleen and kidney. In addition, grass carp immunized with a GCRV-VLPs-based vaccine showed a relative percent survival rate (RPS) of 83.33% after challenge. The data in this study showed that GCRV-VLPs demonstrated an excellent immunogenicity and represent a promising approach for vaccine development against GCRV genotype II infection.

Comparative transcriptome analysis of three invasive leafminer flies provides insights into interspecific competition

Liriomyza spp. (Diptera: Agromyzidae) represent a group of economically-significant highly polyphagous pests of plants grown in field and greenhouse conditions. Liriomyza spp. share similar biological and morphological characteristics, and complex interspecific interactions have been documented among these species in various geographical regions. Where the displacement of one of these species by the other has been studied, no unique mechanisms have been identified as causing it. The impact of competitive factors (such as, insecticide tolerance, thermotolerance, and adaptability to cropping systems) may be unique to specific geographic regions of Liriomyza spp., but more research is needed to confirm these hypotheses. In this study, RNA-seq was used to determine the transcriptomes of three closely-related leafminers, e.g. L. sativae, L. trifolii, and L. huidobrensis. Over 20 Gb of clean reads were generated and assembled into unique transcriptomes, and 38,747 unigenes were annotated in different databases. In pairwise comparisons, L. trifolii and L. sativae had more up-regulated genes than L. huidobrensis. With respect to common differentially-expressed genes (Co-DEGs), the three leafminers exhibited distinct groups of highly-expressed gene clusters. When genes related to competitive factors were compared, expression patterns in L. trifolii and L. sativae were more closely related to each other than to L. huidobrensis. The data suggest that DEGs involved in competitive factors may play a key role in competition and displacement of leafminers. The divergent genes identified in this study will be valuable in revealing possible mechanisms of invasion, displacement and interspecific competition in Liriomyza spp.

Truncated Thioredoxin Peptides Serves as an Efficient Fusion Tag for Production of Proinsulin

BACKGROUND

Insulin is a peptide hormone used for regulating blood glucose levels. Human insulin market is projected to grow at a rate of 12.5% annually. To meet the needs of patients, a cost effective insulin manufacturing strategy has to be developed. This can be achieved by selecting a competent host, ideal fusion tag and streamlined downstream process.

OBJECTIVE

In this article, we have demonstrated that selecting a right fusion partner for expression of toxic proteins like insulin, plays a major role in increasing the recombinant protein yield.

METHODS

In this article, we have focused on identifying a peptide tag fusion partner for expressing proinsulin by truncating thioredoxin tag. Truncations were carried out from both Amino and Carboxy terminus of the protein and efficiency of truncated sequences was evaluated by expressing it with proinsulin gene. FCTRX (1-15) sequence fused to proinsulin was processed further to establish downstream protocol for purification.

RESULTS

Thioredoxin tag was truncated appropriately by considering the fusion tag: protein ratio. A couple of sequences ranging 10 - 15 amino acids were identified based on its in silico properties. Of these FCTRX (1-15) showed increased expression and stability of fusion protein. 156 mg of purified insulin was generated from 1g of inclusion body after enzymatic conversion and chromatographic steps.

CONCLUSION

As a result of the current study, it was concluded that FCTRX (1-15) peptide has advantageous attributes to be considered as an ideal fusion tag for expression of proinsulin. This can be further explored by expressing it with other proteins.

Genetic engineering approaches to improve posttranslational modification of biopharmaceuticals in different production platforms

The number of approved biopharmaceuticals, where product quality attributes remain of major importance, is increasing steadily. Within the available variety of expression hosts, the production of biopharmaceuticals faces diverse limitations with respect to posttranslational modifications (PTM), while different biopharmaceuticals demand different forms and specifications of PTMs for proper functionality. With the growing toolbox of genetic engineering technologies, it is now possible to address general as well as host- or biopharmaceutical-specific product quality obstacles. In this review, we present diverse expression systems derived from mammalians, bacteria, yeast, plants, and insects as well as available genetic engineering tools. We focus on genes for knockout/knockdown and overexpression for meaningful approaches to improve biopharmaceutical PTMs and discuss their applicability as well as future trends in the field.

Expression of hNeuritin protein in a baculovirus expression system and the analysis of its activity

Neuritin plays an important role in the development and regeneration of the nervous system, and shows good prospects in the treatment and protection of the nervous system. To characterize neuritin function, we constructed a baculovirus expression system of neuritin, and identified the biological activity of the neuritin protein. The results and showed that the expression product could promote the neurite growth of dorsal root ganglion in chicken embryos. The neuritin open reading frame was amplified and cloned into the plasmid pFastBac™HTA. The pFastBac™HTA-neuritin was confirmed to be correct by PCR and DNA sequencing, and then transformed into Escherichia coli DH10Bac. The high purity recombinant Bacmid-neuritin (shuttle vectors) was obtained from DH10Bac through screening and identification. Recombinant virus, including the neuritin gene (virus-neuritin), was produced by transfection of SF9 cells using the bacmid-neuritin, and then amplified repeatedly to express the neuritin fusion protein. Finally, we identified the fusion protein with SDS-PAGE and western blotting, and optimized the best expression time of the neuritin fusion protein. We also analyzed the activity of the expressed protein by dorsal root ganglion from chicken embryos.

N-Glycan Modification of a Recombinant Protein via Coexpression of Human Glycosyltransferases in Silkworm Pupae

Recombinant proteins produced in insect cells and insects, unlike those produced in mammalian cells, have pauci-mannose-type N-glycans. In this study, we examined complex-type N-glycans on recombinant proteins via coexpression of human β-1,2-N-acetylglucosaminyltransferase II (hGnT II) and human β1,4-galactosyltransferase (hGalT I) in silkworm pupae, by using the Bombyx mori nucleopolyhedrovirus (BmNPV) bacmid system. The actin A3 promoter from B. mori and the polyhedrin promoter from Autographa californica multiple nucleopolyhedroviruses (AcMNPVs) were used to coexpress hGnT II and hGalT I. These recombinant BmNPVs were coexpressed with human IgG (hIgG), hGnT II and hGalT I in silkworm pupae. When hIgG was coexpressed with hGnT II, approximately 15% of all N-glycans were biantennary, with both arms terminally modified with N-acetylglucosamine (GlcNAc). In contrast, when hIgG was coexpressed with both hGnT II and hGalT I under the control of the polyhedrin promoter, 27% of all N-glycans were biantennary and terminally modified with GlcNAc, with up to 5% carrying one galactose and 11% carrying two. The obtained N-glycan structure was dependent on the promoters used for coexpression of hGnT II or hGalT I. This is the first report of silkworm pupae producing a biantennary, terminally galactosylated N-glycan in a recombinant protein. These results suggest that silkworms can be used as alternatives to insect and mammalian hosts to produce recombinant glycoproteins with complex N-glycans.

Over-expression of secreted proteins from mammalian cell lines

Secreted mammalian proteins require the development of robust protein over-expression systems for crystallographic and biophysical studies of protein function. Due to complex disulfide bonds and distinct glycosylation patterns preventing folding and expression in prokaryotic expression hosts, many secreted proteins necessitate production in more complex eukaryotic expression systems. Here, we elaborate on the methods used to obtain high yields of purified secreted proteins from transiently or stably transfected mammalian cell lines. Among the issues discussed are the selection of appropriate expression vectors, choice of signal sequences for protein secretion, availability of fusion tags for enhancing protein stability and purification, choice of cell line, and the large-scale growth of cells in a variety of formats.

Expression of recombinant antibodies

Recombinant antibodies are highly specific detection probes in research, diagnostics, and have emerged over the last two decades as the fastest growing class of therapeutic proteins. Antibody generation has been dramatically accelerated by in vitro selection systems, particularly phage display. An increasing variety of recombinant production systems have been developed, ranging from Gram-negative and positive bacteria, yeasts and filamentous fungi, insect cell lines, mammalian cells to transgenic plants and animals. Currently, almost all therapeutic antibodies are still produced in mammalian cell lines in order to reduce the risk of immunogenicity due to altered, non-human glycosylation patterns. However, recent developments of glycosylation-engineered yeast, insect cell lines, and transgenic plants are promising to obtain antibodies with "human-like" post-translational modifications. Furthermore, smaller antibody fragments including bispecific antibodies without any glycosylation are successfully produced in bacteria and have advanced to clinical testing. The first therapeutic antibody products from a non-mammalian source can be expected in coming next years. In this review, we focus on current antibody production systems including their usability for different applications.

Use of baculovirus expression system for generation of virus-like particles: successes and challenges

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A brief overview of principles and applications of BES.

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Generation of VLPs using BES.

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Major properties of BES: promoting generation of VLPs.

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Bioprocess considerations for generation of VLPs.

The baculovirus expression system (BES) has been one of the versatile platforms for the production of recombinant proteins requiring multiple post-translational modifications, such as folding, oligomerization, phosphorylation, glycosylation, acylation, disulfide bond formation and proteolytic cleavage. Advances in recombinant DNA technology have facilitated application of the BES, and made it possible to express multiple proteins simultaneously in a single infection and to produce multimeric proteins sharing functional similarity with their natural analogs. Therefore, the BES has been used for the production of recombinant proteins and the construction of virus-like particles (VLPs), as well as for the development of subunit vaccines, including VLP-based vaccines. The VLP, which consists of one or more structural proteins but no viral genome, resembles the authentic virion but cannot replicate in cells. The high-quality recombinant protein expression and post-translational modifications obtained with the BES, along with its capacity to produce multiple proteins, imply that it is ideally suited to VLP production. In this article, we critically review the pros and cons of using the BES as a platform to produce both enveloped and non-enveloped VLPs.

A bi-cistronic baculovirus expression vector for improved recombinant protein production

Baculoviruses are one of the most studied insect viruses both in basic virology research and in biotechnology applications. Incorporating an internal ribosome entry site (IRES) into the baculovirus genome generates bi-cistronic baculoviruses expression vectors that produce two genes of interest. The bi-cistronic baculoviruses also facilitate recombinant virus isolation and titer determination when the green fluorescent protein was co-expressed. Furthermore, when the secretion proteins were co-expressed with the cytosolic green fluorescent protein, the cell lysis and cytosolic protein released into the culture medium could be monitored by the green fluorescence, thus facilitating purification of the secreted proteins.

Improved expression of secreted and membrane-targeted proteins in insect cells

Secretory and membrane-bound proteins are generally produced in lower amounts in insect cells compared with cytoplasmic and nuclear proteins. There may be many reasons for this, including degradation of recombinant proteins by proteases, competition for cellular resources between native and recombinant proteins, and physical blockage of the secretory pathways. In the present study, we describe the construction of a baculovirus in which chiA (chitinase) and cath (cathepsin) genes have been deleted and show improved recombinant protein expression using this vector. We confirmed the complete removal of both genes by PCR, restriction enzyme analysis and enzyme assays, and the modified virus DNA was shown to be stable in bacterial cells over multiple passages. A selection of recombinant genes were inserted into the double-deletion virus and their expression levels compared with recombinant viruses that had single or no gene deletions. In all instances, the double-deletion viruses showed greatly enhanced levels of protein production for both secreted and nuclear/cytoplasmic proteins. In summary, we have conclusively demonstrated the importance of this deletion vector for the high-level production of recombinant proteins.

Improved secretion of molecular chaperone-assisted human IgG in silkworm, and no alterations in their N-linked glycan structures

Human 29IJ6 IgG was expressed in silkworm using a Bombyx mori nucleopolyhedrovirus (BmNPV) bacmid system. The mean amounts of 296IJ6 IgG produced in larval hemolymph and whole pupae were 30.1 microg/larva and 78.0 microg/pupa, respectively. The use of molecular chaperones including calreticulin (CRT), calnexin (CNX), and immunoglobulin heavy chain binding protein (BiP, GRP78) improved the production of 296IJ6 IgG secretion in the larvae fivefold. The total yield of recombinant 29IJ6 IgG was 239 microg/mL when coexpressed with CRT. However, the overexpression of molecular chaperones had negative effects on secretion. The N-linked glycans of secreted 296IJ6 IgG in silkworm hemolymph were dominated by paucimannose structures. Small amounts of GlcNAc residues linked to the Manalpha1,3 branch were detected. When molecular chaperones were coexpressed, the compositions of N-linked glycans in the IgG1 produced were unchanged compared with those produced without them. This suggests that N-glycosylation is controlled by a regulatory function in the Golgi apparatus even though the post-translational modification of 296IJ6 IgG was assisted by the coexpression of molecular chaperones. Therefore, if the glycosylation pathways that coexpress N-acetylglucosaminyltransferase, galactosyltransferase, and sialyltransferase could be improved, silkworm larvae might prove a useful system for producing human antibodies.

Expression of apalbumin1 of Apis cerana cerana in the larvae of silkworm, Bombyx mori

Royal jelly (RJ) is a thick, milky material produced by both the hypopharyngeal and the mandibular glands of nurse honeybees. The main proteins of RJ, named apalbumins or major royal jelly proteins (MRJPs), have multiple biological functions. Apalbumin1 is the most abundant glycoprotein of RJ. In this study, Bacmid- apalbumin1 was constructed for Apis cerana cerana using the newly established Bac-to-Bac/BmNPV baculovirus expression system (BES). This procedure allowed us to obtain the recombinant A. cerana cerana ( Acc) apalbumin1 (r Accapalbumin1) from the hemolymph of silkworm larvae through the BmNPV bacmid system, 96 h postinfection. The r Accapalbumin1 was then purified by Ni-NTA spin columns and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting. A 55 kDa protein with good solubility was then obtained. The peptide Ile-Phe was identified from trypsin production of r Accapalbumin1. Such a peptide has been reported to have an antihypertensive ability. Our results have therefore potential applications in biomedical research and open new perspectives for the study of apalbumins.

Choice of cellular protein expression system

Recombinant protein expression has become a standard laboratory tool, and a wide variety of systems and techniques are now in use. Because there are so many systems to choose from, the investigator has to be careful to use the combination that will give the best results for the protein being studied. This overview unit discusses expression and production choices, including post-translational modifications (e.g., glycosylation, acylation, sulfation, and removal of N-terminal methionine), in vivo and in vitro folding, and influence of downstream elements on expression.

Production of a recombinant antibody fragment in whole insect larvae

Infection of insect cells with baculovirus expression constructs is commonly used to produce recombinant proteins that require post-translational modifications for their activity, such as mammalian proteins. However, technical restraints limit the capacity of insect cell-based culture systems to be scaled up to produce the large amounts of recombinant protein required for human pharmaceuticals. In this study, we designed an automated insect rearing system and whole insect baculovirus expression system (PERLXpress) for the expression and purification of recombinant proteins on a large scale. As a test model, we produced a recombinant mouse anti-botulinum antibody fragment (Fab) in Trichoplusia ni larvae. A recombinant baculovirus co-expressing the Fab heavy and light chains together with N-terminal sequences from the silkworm hormone bombyxin, to direct proteins into the secretory pathway, was constructed. Fifth instar larvae were reared and infected orally with recombinant (pre- occluded) baculovirus using the automated system and harvested approximately after 4 days. The total yield of recombinant Fab was 1.1 g/kg of larvae, resulting in 127 mg of pure Fab in one production run. The Fab was purified to homogeneity using immobilized metal affinity chromatography, gel filtration, and anion exchange chromatography. The identity of the purified protein was verified by Western blots and size-exclusion chromatography. Purified recombinant Fab was used to detect botulinum toxin in ELISA experiments, demonstrating that the heavy and light chains were properly assembled and folded into functional heterodimers. We believe that this is the first demonstration of the expression of a recombinant antibody in whole insect larvae. Our results demonstrate that a baculovirus-whole larvae expression system can be used to express functionally active recombinant Fab fragments. As the PERLXpress system is an automated and linearly scalable technology, it represents an attractive alternative to insect cell culture for the production of large amounts of human pharmaceuticals.

DEVELOPMENT OF AN ENZYME-LINKED IMMUNOELECTROTRANSFER BLOT (EITB) ASSAY USING TWO BACULOVIRUS EXPRESSED RECOMBINANT ANTIGENS FOR DIAGNOSIS OF TAENIA SOLIUM TAENIASIS

Taeniasis diagnosis is an important step in the control and elimination of both cysticercosis and taeniasis. We report the development of 2 serological taeniasis diagnostic tests using recombinant antigens rES33 and rES38 expressed by baculovirus in insect cells in an EITB format. In laboratory testing with defined sera from nonendemic areas, rES33 has a sensitivity of 98% (n = 167) and a specificity of 99% (n = 310) (J index: 0.97); rES38 has a sensitivity of 99% (n = 146) and a specificity of 97% (n = 275) (J index: 0.96). Independent field testing in Peru showed 97% (n = 203) of the taeniasis sera were positive with rES33, and 100% of the nontaeniasis sera (n = 272) were negative with rES33; 98% (n = 198) of taeniasis sera were positive with rES38, and 91% (n = 274) of the nontaeniasis sera were negative with rES38. Among the Peruvian sera tested, 17 of 26 Peruvian Taenia saginata sera were false positive with rES38 test. Both tests were also examined with cysticercosis sera, with a positive rate ranging from 21% to 46%. rES33 and rES38 tests offer sensitive and specific diagnosis of taeniasis and easy sample collection through finger sticks that can be used in large-scale studies. They are currently being used in cysticercosis elimination programs in Peru.

Secretory fluorescent protein, a secretion green fluorescent fusion protein with alkaline phosphatase activity as a sensitive and traceable reporter in baculovirus expression system

The advantages of using traceable fluorescent protein (enhanced green fluorescent protein; EGFP) and a secretory alkaline phosphatase (SEAP) have been used to generate a reporter gene: the secretory fluorescent protein (SEFP). Sf21 cells, infected with the recombinant baculovirus containing the SEFP gene, revealed both traceable fluorescence and easily detectable alkaline phosphatase activity in the culture medium. The distribution of SEFP within the cells revealed that it was excluded from the nucleus, implying that the accumulation of SEFP in a secretory pathway, similar to that of the secretion signal-tagged FPs. Furthermore, the time- and dose-dependent release from the blockage of brefeldin A (BFA) confirmed that the secretion of SEFP was mediated by the secretion pathway and excluded leakage from viral infection. This SEFP reporter gene with traceable fluorescence and alkaline phosphatase activity may become a useful tool for studies on secretory protein production.

Transforming lepidopteran insect cells for improved protein processing

The lepidopteran insect cells used with the baculovirus expression vector system (BEVS) are capable of synthesizing and accurately processing foreign proteins. However, proteins expressed in baculovirus-infected cells often fail to be completely processed, or are not processed in a manner that meets a researcher's needs. This chapter discusses a metabolic engineering approach that addresses this problem. Basically, this approach involves the addition of new or enhancement of existing protein processing functions in established lepidopteran insect cell lines. Methods for engineering these cell lines and assessing their properties as improved hosts for the BEVS are detailed. Examples of lepidopteran insect cell lines engineered for improved protein N-glycosylation and trafficking are described.

High cell density fed batch and perfusion processes for stable non-viral expression of secreted alkaline phosphatase (SEAP) using insect cells: Comparison to a batch Sf-9-BEV system

The development of insect cells expressing recombinant proteins in a stable continuous manner is an attractive alternative to the BEV system for recombinant protein production. High cell density fed batch and continuous perfusion processes can be designed to maximize the productivity of stably transformed cells. A cell line (Sf-9SEAP) expressing high levels of the reporter protein SEAP stably was obtained by lipid-mediated transfection of Sf-9 insect cells and further selection and screening. The expression of the Sf-9SEAP cells was compared with the BEVS system. It was observed that, the yield obtained in BEVS was similar to the batch Sf-9SEAP at 8 and 7 IU/mL, respectively. The productivity of this foreign gene product with the stable cells was enhanced by bioprocess intensification employing the fed-batch and perfusion modes of culture to increase the cell density in culture. The fed batch process yielded a maximum cell density of 28 x 10(6) cells/mL and 12 IU/mL of SEAP. Further improvements in the productivity could be made using the perfusion process, which demonstrated a stable production rate for extended periods of time. The process was maintained for 43 days, with a steady-state cell density of 17-20 x 10(6) cells/mL and 7 IU/mL SEAP. The total yield obtained in the perfusion process (394 IU) was approximately 22 and 8 times higher than that obtained in a batch (17.6 IU) and fed batch (46.1 IU) process, respectively.

The insect metalloproteinase inhibitor gene of the lepidopteran Galleria mellonella encodes two distinct inhibitors

The insect metalloproteinase inhibitor (IMPI) from the greater wax moth, Galleria mellonella, represents the first and to date only specific inhibitor of microbial metalloproteinases reported from animals. Here, we report on the characterization including carbohydrate analysis of two recombinant constructs encoded by impi cDNA either upstream or downstream of the furin cleavage site identified. rIMPI-1, corresponding to native IMPI purified from hemolymph, is encoded by the N-terminal part of the impi sequence, whereas rIMPI-2 is encoded by its C-terminal part. rIMPI-1 is glycosylated at N48 with GlcNAc2Man3, showing fucosylation to different extents. Similarly, rIMPI-2 is glycosylated at N149 with GlcNAc2Man3, but is fully fucosylated. rIMPI-1 represents a promising template for the design of second-generation antibiotics owing to its specific activity against thermolysin-like metalloproteinases produced by human pathogenic bacteria such as Vibrio vulnificus. In contrast, rIMPI-2 does not inhibit bacterial metalloproteinases, but is moderately active against recombinant human matrix metalloproteinases (MMPs). Both microbial metalloproteinases and MMPs induce expression of the impi gene when injected into G. mellonella larvae. These findings provide evidence that the impi gene encodes two distinct inhibitors, one inhibiting microbial metalloproteinases and contributing to innate immunity, the other putatively mediating regulation of endogenous MMPs during metamorphosis.

Comparison of different signal peptides for protein secretion in nonlytic insect cell system

Protein expression and secretion in insect cells have been widely studied in the baculovirus-infected insect cell system. In directly transfected insect cells only intracellular expression and purification of recombinant proteins have been studied in detail. To examine multiple recombinant protein variants, easy and fast expression and a purification screening system are required. The aim of this study was to establish an effective and rapid secretion system for human azurocidin using directly transfected insect cells. We also constructed and tested expression vectors possessing heterologous signal peptides derived from human azurocidin, yellow lupin diphosphonucleotide phosphatase/phosphodiesterase (PPD1), and papaya papain IV to secrete yellow lupin and red kidney bean purple acid phosphatases, PPD1, and papain IV. Our results demonstrate that the secretion vectors used here can direct recombinant proteins to the culture medium very effectively, allowing their simple purification on a small/medium scale. Based on secretion and activity analyses it seems that the azurocidin signal peptide is one of the most potent secretion signals.

Identification of core 1 O-glycan T-synthase from Caenorhabditis elegans

The common O-glycan core structure in animal glycoproteins is the core 1 disaccharide Galbeta1-3GalNAcalpha1-Ser/Thr, which is generated by the addition of Gal to GalNAcalpha1-Ser/Thr by core 1 UDP-alpha-galactose (UDP-Gal):GalNAcalpha1-Ser/Thr beta1,3-galactosyltransferase (core 1 beta3-Gal-T or T-synthase, EC2.4.1.122). Although O-glycans play important roles in vertebrates, much remains to be learned from model organisms such as the free-living nematode Caenorhabditis elegans, which offer many advantages in exploring O-glycan structure/function. Here, we report the cloning and enzymatic characterization of T-synthase from C. elegans (Ce-T-synthase). A putative C. elegans gene for T-synthase, C38H2.2, was identified in GenBank by a BlastP search using the human T-synthase protein sequence. The full-length cDNA for Ce-T-synthase, which was generated by polymerase chain reaction using a C. elegans cDNA library as the template, contains 1170 bp including the stop TAA. The cDNA encodes a protein of 389 amino acids with typical type II membrane topology and a remarkable 42.7% identity to the human T-synthase. Ce-T-synthase has seven Cys residues in the lumenal domain including six conserved Cys residues in all orthologs. The Ce-T-synthase has four potential N-glycosylation sequons, whereas the mammalian orthologs lack N-glycosylation sequons. Only one gene for Ce-T-synthase was identified in the genome-wide search, and it contains eight exons. Promoter analysis of the Ce-T-synthase using green fluorescent protein (GFP) constructs shows that the gene is expressed at all developmental stages and appears to be in all cells. Unexpectedly, only minimal activity was recovered in the recombinant, soluble Ce-T-synthase secreted from a wide variety of mammalian cell lines, whereas robust enzyme activity was recovered in the soluble Ce-T-synthase expressed in Hi-5 insect cells. Vertebrate T-synthase requires the molecular chaperone Cosmc, but our results show that Ce-T-synthase does not require Cosmc and might require invertebrate-specific factors for the formation of the optimally active enzyme. These results show that the Ce-T-synthase is a functional ortholog to the human T-synthase in generating core 1 O-glycans and open new avenues to explore O-glycan function in this model organism.

New tools for G-protein coupled receptor (GPCR) drug discovery: combination of baculoviral expression system and solid state NMR

Biotechnology using molecular biology, biochemistry, biophysics, and computational approaches provides an alternative approach for classical pharmacological screening to look at ligand-receptor interactions and receptor specificity, which should support the design of selective drugs based on detailed structural principles. This review addresses specific approaches to study function, structure and relevance of a major pharmaceutical target, namely the G-Protein Coupled Receptors (GPCRs). The main aim of this review has been to exploit and combine GPCR over-expression in a baculoviral expression system with solid-state MAS NMR (ssNMR) approaches for the elucidation of electronic structures of the coordinating ligands/drugs and their modes of interactions with the GPCRs. This review summarizes the approaches, possible future experiments and developments using the above combination of tools for GPCR drug discovery.

Functional expression of streptococcal galactosyltransferase in baculovirus/insect cell expression system

The cpsIaJ gene of Streptococcus agalactiae type Ia codes for beta-1,4-galactosyltransferase. In this study, the functional expression of His-tagged CpsIaJ in a baculovirus expression system was performed, because the efficient functional expression of this enzyme in Escherichia coli had been unsuccessful. Using a partially purified enzyme preparation, we found that the enzyme had a restricted substrate specificity and that the entire structure of the substrate GlcNAc beta1-3Gal beta1-4Glc was required for the activity. Furthermore, mutations in a conserved DXD motif caused the loss of the enzyme's activity.

Secretion of human glucocerebrosidase from stable transformed insect cells using native signal sequences

The lysosomal hydrolase, glucocerebrosidase (GBA), catalyses the penultimate step in the breakdown of membrane glycosphingolipids. An inherited deficiency of this enzyme activity leads to the onset of Gaucher disease, the most common lysosomal storage disorder. Affected individuals range from adults with hepatosplenomegaly, haematological complications, and bone pain (type 1 disease) to children and neonates with severe neuronopathy leading to neurological degradation and premature death (type 2 and type 3 disease). Enzyme replacement therapy has become the standard of treatment for type I Gaucher disease but remains an expensive option, in part because of the cost of recombinant enzyme production using mammalian cell culture. Using a nonlytic integrative plasmid expression system, we have successfully produced active human GBA in stable transformed Sf9 (Spodoptera frugiperda) cells. Both the 39 and 19 amino acid native GBA signal sequences were capable of endoplasmic reticulum targeting, which led to secretion of the recombinant protein, although approximately 30% more enzyme was produced using the longer signal sequence. The secreted product was purified to apparent electrophoretic homogeneity using hydrophobic interaction chromatography and found to be produced in a fully glycosylated and a hypoglycosylated form, both of which cross-reacted with a human GBA-specific monoclonal antibody. The pH optimum (at pH 5.5) for activity of the recombinant enzyme was as expected for human GBA using the artificial substrate 4-methyl-umbelliferyl-β-D-glycopyranoside. With initial nonoptimized expression levels estimated at 10–15 mg/L using small-scale batch cultures, stable transformed insect cells could provide a viable alternative system for the heterologous production of human GBA when grown under optimized perfusion culture conditions.Key words: Gaucher disease, glucocerebrosidase, protein expression, enzyme purification, Sf9 cells.

Changes in cellular secretory processing during baculovirus infection

In the baculovirus expression vector system (BEVS), secretory green fluorescent protein (sGFP) transcripts were expressed from day 2 to day 5 post-infection (p.i.), while transcripts of the endoplasmic reticulum (ER) molecular chaperone Bombyx mori protein disulfide isomerase (bPDI) were measurable in mock cells and in cells at day 1 p.i. The GFP was expressed from day 3 to day 5 p.i. whereas the levels of two ER chaperone proteins, bPDI and calnexin, decreased from day 3 p.i. and were not detected from day 4 p.i. These findings suggest that the rate-limited expression of ER molecular chaperones is strongly associated with the maximal expression of exogenous proteins in BEVS.

Polydnavirus Genes that Enhance the Baculovirus Expression Vector System

The baculovirus expression vector system (BEVS) is a powerful and versatile system for protein expression, which has many advantages. However, a limitation of any lytic viral expression system, including BEVS, is that death and lysis of infected insect cells terminates protein production. This results in interruption of protein production and higher production costs due to the need to set up new infections, maintain uninfected cells, and produce pure viral stocks. Genetic methods to slow or prevent cell death while maintaining high-level, virus-driven protein production could dramatically increase protein yields. Several approaches have been used to improve the BEVS and increase the synthesis of functional proteins. Successful enhancement of the BEVS was obtained when various gene elements were added to the virus, secretion and posttranslational processing were modified, or protein integrity was improved. A gene family from the insect virus Campoletis sonorensis ichnovirus (CsIV) was discovered that delays lysis of baculovirus-infected cells, thereby significantly enhancing recombinant protein production in the BEVS system. By using the CsIV vankyrin gene family, protein production in the vankyrin-enhanced BEVS (VE-BEVS) was increased by a factor of 4- to 15-fold by either coexpressing the vankyrin protein from a dual BEVS or by providing its activity in trans by expressing the vankyrin protein from a stably transformed cell line. In sum, VE-BEVS is an enhancement of the existing BEVS technology that markedly improves protein expression levels while reducing the cost of labor and materials.

Development of a bi-cistronic baculovirus expression vector by the Rhopalosiphum padi virus 5' internal ribosome entry site

A bi-cistronic baculovirus transfer vector was constructed based on the 5'UTR internal ribosome entry site (IRES) of the Rhopalosiphum padi virus (RhPV). Recombinant baculoviruses containing the red fluorescent protein gene and green fluorescent protein gene flanking the RhPV 5'UTR IRES can simultaneously produce dual fluorescence in recombinant virus-infected Spodoptera frugiperda 21 cells (Sf21) under the control of a polyhedrin promoter. Quantization by fluorescence spectrophotometry of the fluorescent proteins produced in Sf21 cells indicated that the translational efficacy of the RhPV 5'UTR IRES was about 3-fold weaker than cap-dependent translation. We also demonstrated that recombinant baculoviruses containing the human interferon-gamma gene (IFN-gamma) and green fluorescent protein gene flanking the RhPV 5'UTR IRES can produce IFN-gamma proteins as well as green fluorescent proteins. These results suggest that the RhPV IRES can be used in the development of bi-cistronic baculovirus expression vectors for production of heterologous multiprotein complexes or can be combined with selection markers to facilitate applications of baculovirus expression systems.

Baculovirus as versatile vectors for protein expression in insect and mammalian cells

Today, many thousands of recombinant proteins, ranging from cytosolic enzymes to membrane-bound proteins, have been successfully produced in baculovirus-infected insect cells. Yet, in addition to its value in producing recombinant proteins in insect cells and larvae, this viral vector system continues to evolve in new and unexpected ways. This is exemplified by the development of engineered insect cell lines to mimic mammalian cell glycosylation of expressed proteins, baculovirus display strategies and the application of the virus as a mammalian-cell gene delivery vector. Novel vector design and cell engineering approaches will serve to further enhance the value of baculovirus technology.

Functional expression of a multidrug P-glycoprotein transporter of Leishmania

P-glycoprotein (Pgp) transporters play an important role in multidrug resistance in eukaryotic cells and in protozoan parasites such as Leishmania. To search for new reversal agents of the Leishmania tropica Pgp, we developed a screening assay using the Baculovirus-insect cell expression system. We demonstrated a MgATP-dependent, vanadate-sensitive transport of Hoechst 33342 in membrane preparations of Sf9 insect cells expressing Pgp. We have found that dihydro-beta-agarofuran sesquiterpenes from Maytenus cuzcoina inhibited Hoechst 33342 transport that correlates with their reversal effect in a multidrug-resistant L. tropica line overexpressing Pgp. The results suggest that Sf9 cell membrane Hoechst 33342 transport system represents an efficient tool for examining the interactions of Leishmania Pgp with pharmacological agents.

Enhancement of correct protein folding in vivo by a non-lytic baculovirus

The BEVS (baculovirus expression vector system) is widely used for the production of proteins. However, engineered proteins frequently experience the problem of degradation, possibly due to the lytic nature of the conventional BEVS (herein referred to as L-BEVS). In the present study, a non-lytic BEVS (N-BEVS) was established by random mutagenesis of viral genomes. At 5 days post-infection, N-BEVS showed only 7% cell lysis, whereas L-BEVS showed 60% lysis of cells. The quality of protein expressed in both N- and L-BEVSs was examined further using a novel FRET (fluorescence resonance energy transfer)-based assay. To achieve this, we constructed a concatenated fusion protein comprising LUC (luciferase) sandwiched between EYFP (enhanced yellow fluorescent protein) and ECFP (enhanced cyan fluorescent protein). The distance separating the two fluorescent proteins in the fusion protein EYFP-LUC-ECFP (designated hereafter as the YLC construct) governs energy transfer between EYFP and ECFP. FRET efficiency thus reflects the compactness of LUC, indicating its folding status. We found more efficient FRET in N-BEVS compared with that obtained in L-BEVS, suggesting that more tightly folded LUC was produced in N-BEVS. YLC expression was also analysed by Western blotting, revealing significantly less protein degradation in N-BEVS than in L-BEVS, in which extensive degradation was observed. This FRET-based in vivo folding technology showed that YLC produced in N-BEVS is more compact, correlating with improved resistance to degradation. N-BEVS is thus a convenient alternative for L-BEVS for the production of proteins vulnerable to degradation using baculoviruses.

Production of recombinant proteins by vaccinia virus in a microcarrier based mammalian cell perfusion bioreactor

The HeLa cell-vaccinia virus expression system was evaluated for the production of recombinant proteins (enhanced green fluorescent protein (EGFP) and HIV envelope coat protein, gp120) using microcarriers in 1.5 L perfused bioreactor cultures. Perfusion was achieved by use of an alternating tangential flow device (ATF), increasing the length of the exponential phase by 50 h compared to batch culture and increasing the maximum cell density from 1.5x10(6) to 4.4x10(6) cell/mL. A seed train expansion method using cells harvested from microcarrier culture and reseeding onto fresh carriers was developed. EGFP was first used as a model protein to study process parameters affecting protein yield, specifically dissolved oxygen (DO) and temperature during the production phase. The highest level of EGFP, 12+/-1.5 microg/10(6) infected cells, was obtained at 50% DO and 31 degrees C. These setpoints were then used to produce glycoprotein, gp120, which was purified and deglycosylated, revealing a significant amount of N-linked glycosylation. Also, biological activity was assayed, resulting in an ID50 of 3.1 microg/mL, which is comparable to previous reports.

Advances in genome-wide protein expression using the wheat germ cell-free system

In the current post-genomic era, cell-free translation platforms are gaining importance in structural as well as functional genomics. They are based on extracts prepared from Escherichia coli cells, wheat germ, or rabbit reticulocytes, and when programmed with any mRNA in the presence of energy sources and amino acids, can synthesize the respective protein in vitro. Among the cell-free systems, the wheat germ-based translation system is of special interest due to its eukaryotic nature and robustness. This chapter outlines the existing protein production platforms and their limitations, and describes the basic concept of the wheat germ-based cell-free system. It also demonstrates how the conventional wheat germ system can be improved by eliminating endogenous inhibitors, by using an expression vector specially designed for this system and polymerase chain reaction-directed protein synthesis directly from cDNAs in a bi-layer translation system. Finally, a robotic procedure for translation based on the wheat germ extract and bi-layer cell-free translation is described.

High level production and one-step purification of biologically active ectodysplasin A1 and A2 immunoadhesins using the baculovirus/insect cell expression system

Ectodysplasin A (EDA) is a ligand of the tumor necrosis factor (TNF) family that has been shown to play a crucial role in ectodermal differentiation. Mutations of the syntenic ectodysplasin A gene (Eda) are responsible for Tabby (Ta) phenotype in mice and human X-linked hypohidrotic ectodermal dysplasia (XLHED). EDA-A1 and EDA-A2 are the two main splice variants of Eda, which differ from each other in only two amino acid residues and engage the tumor necrosis factor (TNF) family receptors EDAR and XEDAR, respectively. We have used the baculovirus/insect cell system to express the recombinant EDA proteins fused to the Fc portion of a truncated human IgG1 immunoglobulin heavy chain. Immunoadhesins (4.5-4.7 mg/L) from crude supernatant could be purified to near homogeneity by using rProtein A affinity chromatography. The purified EDA immunoadhesins were endowed with ligand-binding activity as they could bind EDAR or XEDAR on the surface of 293T cells that had been transiently transfected with the corresponding plasmids. Functional activities of EDA immunoadhesins were demonstrated by their ability to activate the NF-kappaB pathway in cells expressing their cognate receptors. These results open up the possibility of obtaining large amounts of purified EDA proteins to investigate EDAR/XEDAR related signaling pathways and for the treatment of patients with X-linked hypohidrotic ectodermal dysplasia.