Purification and Characterization of Human DNA Ligase IIIα Complexes After Expression in Insect Cells

With improvements in biophysical approaches, there is growing interest in characterizing large, flexible multi-protein complexes. The use of recombinant baculoviruses to express heterologous genes in cultured insect cells has advantages for the expression of human protein complexes because of the ease of co-expressing multiple proteins in insect cells and the presence of a conserved post-translational machinery that introduces many of the same modifications found in human cells. Here we describe the preparation of recombinant baculoviruses expressing DNA ligase IIIα, XRCC1, and TDP1, their subsequent co-expression in cultured insect cells, the purification of complexes containing DNA ligase IIIα from insect cell lysates, and their characterization by multi-angle light scattering linked to size exclusion chromatography and negative stain electron microscopy.

A review of alternative promoters for optimal recombinant protein expression in baculovirus-infected insect cells

Generating recombinant proteins in insect cells has been made possible via the use of the Baculovirus Expression Vector System (BEVS). Despite the success of many proteins via this platform, some targets remain a challenge due to issues such as cytopathic effects, the unpredictable nature of co-infection and co-expressions, and baculovirus genome instability. Many promoters have been assayed for the purpose of expressing diverse proteins in insect cells, and yet there remains a lack of implementation of those results when reviewing the landscape of commercially available baculovirus vectors. In advancing the platform to produce a greater variety of proteins and complexes, the development of such constructs cannot be avoided. A better understanding of viral gene regulation and promoter options including viral, synthetic, and insect-derived promoters will be beneficial to researchers looking to utilize BEVS by recruiting these intricate mechanisms of gene regulation for heterologous gene expression. Here we summarize some of the developments that could be utilized to improve the expression of recombinant proteins and multi-protein complexes in insect cells.

Construction of the Antheraea pernyi (Lepidoptera: Saturniidae) Multicapsid Nucleopolyhedrovirus Bacmid System

In this study, we established the Antheraea pernyi multicapsid nucleopolyhedrovirus (AnpeNPV) bacmid system for the construction of a Bac-to-Bac expression system and the generation of virus mutants. The CopyRight pSMART BAC cloning vector harboring the chloramphenicol resistance gene was introduced into the AnpeNPV genome to produce the AnpeNPV bacmid that could be propagated in Escherichia coli with stable replication. The enhanced green fluorescent protein (EGFP) was successfully expressed in both Tn-Hi5 cells and A. pernyi pupae using the AnpeNPV Bac-to-Bac expression system. To generate the AnpeNPV mutants, we developed the AnpeNPV bacmid/λ Red recombination system that facilitated the deletion of viral genes from the AnpeNPV genome. The genes cathepsin and chitinase were deleted and a derivative AnpeNPV Bac-to-Bac expression system was constructed. Furthermore, we demonstrated that the novel expression system could be used to express human epidermal growth factor in A. pernyi pupae. Taken together, the AnpeNPV bacmid system provides a powerful tool to create the AnpeNPV Bac-to-Bac expression system for protein expression in A. pernyi pupae. Further, it helps to knock-out genes from the AnpeNPV genome with λ Red recombination system for identification of the role of viral genes involved in regulating gene expression, DNA replication, virion structure, and infectivity during the AnpeNPV infection process.

Neospora caninum antigens displaying virus-like particles as a bivalent vaccine candidate against neosporosis

Neospora caninum is a causative and transmissible agent of dog and bovine neosporosis. The resulting reproductive failures in infected cattle lead to significant economic losses worldwide. However, there is no satisfactory treatment or vaccine currently available to combat this pathogen. Thus, the development of appropriate vaccines to manage its infection and transmission is urgently needed. In this study, we expressed Rous sarcoma virus-like particles (RSV-LP) that displayed dual N. caninum antigens in silkworms. The antigen candidates are modified by adding a transmembrane domain of GP64 protein from Bombyx mori nucleopolyhedrovirus (BmNPV) to the C-terminus of surface antigen 1 (NcSAG1) and SAG1-related sequence 2 (NcSRS2). The NcSRS2 alone or the NcSAG1/NcSRS2 bivalent form displaying RSV-LPs were purified using sucrose density gradient centrifugation. These purified VLPs were then used for immunizations in gerbils, Meriones unguiculatus, to evaluate the anti-N. caninum effects in vivo. The results demonstrated that antigens displaying RSV-LPs in immunized gerbils produced the antigen-specific antibody, leading to a relatively lower parasite load after infections of N. caninum. To the best of our knowledge, this is the first study to present an RSV-LP vaccine displaying bivalent antigens from neosporosis. Taken together, our strategy suggests that silkworm-expressed virus-like particles (VLPs) are promising bivalent vaccine candidates against N. caninum infections.

Formation of Virus-Like Particles of the Dengue Virus Serotype 2 Expressed in Silkworm Larvae

To explore virus-like particles formation of dengue virus serotype type 2 (DENV-2) structural proteins of, C, prM, E were expressed in silkworm larvae using recombinant Bombyx mori nucleopolyhedroviruses (BmNPV). Each recombinant BmNPV bacmid coding the 2C-prM-E polypeptide and E protein fused with the signal peptide of bombyxin from B. mori was injected into silkworm larvae. The expressed proteins were collected from hemolymph and fat body, and purified using affinity chromatography. E protein was observed at 55 kDa. The DENV virus-like particles (DENV-LPs) with a diameter approximately 35 nm was observed using transmission electron microscopy (TEM) and immunogold-labelling TEM analysis. The binding of each partially purified proteins to heparin, one of receptors for DENV was confirmed. DENV-LPs were secreted in silkworm larval hemolymph even still low amount, but the E protein and heparin binding function were confirmed.

Designing Two Individual AcMNPV Polyhedrin-Plus Bac-to-Bac Expression System in order to Express GFP and CPV-VP2 in Insect Cells

Background: The importance of viral protein-2 (VP2) of canine parvovirus (CPV) in binding to human cancer cells, production of veterinary vaccines and diagnostic kits has motivated several researches on producing this protein. Objectives: Our purpose was to construct recombinant bacmid shuttle vectors expressing VP2 of CPV using Bac-to-Bac baculoviral expression system. Materials and Methods: Mini-Tn7 transposones engineered in pFastBac1 donor vectors were used to construct expression cassettes of GFP and CPV-VP2. The plasmids were transferred into E. coli DH₁₀Bac competent cells. Site-specific transposition of the genes into bacmid was accomplished using helper plasmid. Occurrence of Transposition was confirmed via PCR using specific primers and PUC/M₁₃ universal primers. The recombinant bacmid DNAs were transfected into Sf9 cells using cationic lipids to generate new recombinant baculoviruses expressing GFP and CPV-VP2. GFP and VP2 expressions were evaluated by fluorescence microscopy and western analysis, respectively. Results: Cloning, subcloning and recombination processes of both GFP and VP2 were accomplished and verified. Accuracy of transfection process was confirmed by GFP fluorescence microscopy.VP2 expression was verified by SDS-PAGE and western analysis. Conclusions: Two Bac-to-Bac expression systems were designed to produce recombinant VP2 and GFP in insect cells.

Development of a baculovirus vector carrying a small hairpin RNA for suppression of sf-caspase-1 expression and improvement of recombinant protein production

Background

The Baculovirus expression vector system (BEVS) is a transient expression platform for recombinant protein production in insect cells. Baculovirus infection of insect cells will shutoff host translation and induce apoptosis and lead to the termination of protein expression. Previous reports have demonstrated the enhancement of protein yield in BEVS using stable insect cell lines expressing interference RNA to suppress the expression of caspase-1.

Results

In this study, short-hairpin RNA (shRNA) expression cassettes targeting Spodoptera frugiperda caspase-1 (Sf-caspase-1) were constructed and inserted into an Autographa californica multiple nucleopolyhedrovirus (AcMNPV) vector. Using the recombinant baculovirus vectors, we detected the suppression of Sf-caspase-1 expression and cell apoptosis. Green fluorescent protein (GFP), Discosoma sp. Red (DsRed) and firefly luciferase were then expressed as reporter proteins. The results showed that suppression of apoptosis enhanced the accumulation of exogenous proteins at 2 and 3 days post infection. After 4 days post infection, the activity of the reporter proteins remained higher in BEVS using the baculovirus carrying shRNA in comparison with the control without shRNA, but the accumulated protein levels showed no obvious difference between them, suggesting that apoptosis suppression resulted in improved protein folding rather than translation efficiency at the very late stage of baculovirus infection.

Conclusions

The baculovirus vector developed in this study would be a useful tool for the production of active proteins suitable for structural and functional studies or pharmaceutical applications in Sf9 cells, and it also has the potential to be adapted for the improvement of protein expression in different insect cell lines that can be infected by AcMNPV.

Introduction of cationic virosome derived from vesicular stomatitis virus as a novel gene delivery system for sf9 cells

Insect-derived cell lines are used extensively to produce recombinant proteins because they are capable of performing a range of post-translational modifications. Due to their significance in biotechnological applications, various methods have been developed to transfect them. In this study, we introduce a virosome constructed from vesicular stomatitis virus (VSV) as a new delivery system for sf9 cells. We labeled these VSV virosomes by fluorescent probe Rhodamine B chloride (R18). By fluorescence microscope observation and conducting a fusion assay, we confirmed the uptake of VSV virosomes via endocytosis by sf9 cells and their fusion with the endosomal membrane. Moreover, we incubated cationic VSV virosomes with a GFP-expressing bacmid and transfected sf9 cells, after 24 h some cells expressed GFP indicating the ability of VSV virosomes to deliver heterologous DNA to these cells. This is the first report of a virosome-based delivery system introduced for an insect cell line.

High-Throughput Baculovirus Expression System for Membrane Protein Production

The ease of use, robustness, cost-effectiveness, and posttranslational machinery make baculovirus expression system a popular choice for production of eukaryotic membrane proteins. This system can be readily adapted for high-throughput operations. This chapter outlines the techniques and procedures for cloning, transfection, small-scale production, and purification of membrane protein samples in a high-throughput manner.