Expression of tomato yellow leaf curl virus coat protein using baculovirus expression system and evaluation of its utility as a viral antigen

Accelerated Long-Fragment Circular PCR for Genetic Manipulation of Plant Viruses in Unveiling Functional Genomics

Molecular cloning, a crucial prerequisite for engineering plasmid constructs intended for functional genomic studies, relies on successful restriction and ligation processes. However, the lack of unique restriction sites often hinders construct preparation, necessitating multiple modifications. Moreover, achieving the successful ligation of large plasmid constructs is frequently challenging. To address these limitations, we present a novel PCR strategy in this study, termed 'long-fragment circular-efficient PCR' (LC-PCR). This technique involves one or two rounds of PCR with an additional third-long primer that complements both ends of the newly synthesized strand of a plasmid construct. This results in self-circularization with a nick-gap in each newly formed strand. The LC-PCR technique was successfully employed to insert a partial sequence (210 nucleotides) of the phytoene desaturase gene from Nicotiana benthamiana and a full capsid protein gene (770 nucleotides) of a begomovirus (tomato leaf curl New Delhi virus) into a 16.4 kb infectious construct of a tobamovirus, cucumber green mottle mosaic virus (CGMMV), cloned in pCambia. This was done to develop the virus-induced gene silencing vector (VIGS) and an expression vector for a foreign protein in plants, respectively. Furthermore, the LC-PCR could be applied for the deletion of a large region (replicase enzyme) and the substitution of a single amino acid in the CGMMV genome. Various in planta assays of these constructs validate their biological functionality, highlighting the utility of the LC-PCR technique in deciphering plant-virus functional genomics. The LC-PCR is not only suitable for modifying plant viral genomes but also applicable to a wide range of plant, animal, and human gene engineering under in-vitro conditions. Additionally, the LC-PCR technique provides an alternative to expensive kits, enabling quick introduction of modifications in any part of the nucleotide within a couple of days. Thus, the LC-PCR proves to be a suitable 'all in one' technique for modifying large plasmid constructs through site-directed gene insertion, deletion, and mutation, eliminating the need for restriction and ligation.

Plant and insect virus-like particles: emerging nanoparticles for agricultural pest management

Virus-like particles (VLPs) represent a biodegradable, biocompatible nanomaterial made from viral coat proteins that can improve the delivery of antigens, drugs, nucleic acids, and other substances, with most applications in human and veterinary medicine. Regarding agricultural viruses, many insect and plant virus coat proteins have been shown to assemble into VLPs accurately. In addition, some plant virus-based VLPs have been used in medical studies. However, to our knowledge, the potential application of plant/insect virus-based VLPs in agriculture remains largely underexplored. This review focuses on why and how to engineer coat proteins of plant/insect viruses as functionalized VLPs, and how to exploit VLPs in agricultural pest control. The first part of the review describes four different engineering strategies for loading cargo at the inner or the outer surface of VLPs depending on the type of cargo and purpose. Second, the literature on plant and insect viruses the coat proteins of which have been confirmed to self-assemble into VLPs is reviewed. These VLPs are good candidates for developing VLP-based agricultural pest control strategies. Lastly, the concepts of plant/insect virus-based VLPs for delivering insecticidal and antiviral components (e.g., double-stranded RNA, peptides, and chemicals) are discussed, which provides future prospects of VLP application in agricultural pest control. In addition, some concerns are raised about VLP production on a large scale and the short-term resistance of hosts to VLP uptake. Overall, this review is expected to stimulate interest and research exploring plant/insect virus-based VLP applications in agricultural pest management. © 2023 Society of Chemical Industry.

Homologous recombination risk in baculovirus expression vector system

The baculovirus expression vector system (BEVS) is widely used for producing recombinant proteins. To achieve high expression level of recombinant proteins, baculoviral elements, such as enhancers, promoters, signal peptide coding sequences and 3'-UTR, have been extensively employed. There is a recombination risk derived from homologous sequences between viral genome and functional baculovirus-derived elements associated with foreign genes. Although homologous recombination have distinct biological functions, these potential adverse recombination may trigger a DNA fragment being inverted or looped out, resulting in the production of defective viruses and eventual yields declines of recombinant proteins. However, the risk of such homologous recombination has not been systematically assessed. Here, we measured the recombination rate using a promoter-less fluorescent reporter integrated with various lengths homologous of p10 coding region. Homologous fragments longer than 60 bp possess sufficient recombination probability and exerts effect on purity and integrity of virus. Shortening the length of homologous fragments and separating homologous fragments by point mutations can effectively reduce unfavorable recombination. These findings reveal a homologous recombination risk resulted from genome-homologous baculoviral elements and propose reliable strategies reducing recombination rate to facilitate viral stability and integrity in baculovirus expression vector system.

A gold nanoparticles-based lateral flow assay utilizing baculovirus expressed recombinant nucleocapsid and receptor binding domain proteins for serodetection of IgG and IgM against SARS-CoV-2

Serological assays for SARS-CoV-2 are being utilized at an exponential rate for surveillance programs. This enterprise was designed to develop and validate a qualitative immunochromatographic test, via the Lateral Flow Assay (LFA), for detection of immunoglobulins M and G (IgM and IgG) against both nucleocapsid (N) and the receptor-binding domain (RBD) of the spike protein of SARS-CoV-2. Both targeted proteins were cloned and expressed in baculovirus expression system utilizing insect cells Sf9. The recombinant RBD and N proteins were purified and conjugated with gold nanoparticles (AuNPs) to set up the coating antigens pad. Both anti-human IgG and IgM were dispensed on nitrocellulose membrane to capture human antibodies in serum samples. A home-made dispensing system was developed to draw identical test and control lines. The validity of the developed LFA was verified by testing serum samples from 103 convalescent COVID-19 patients who were PCR positive for SARS-CoV-2 along with 28 control serum samples. The developed strips showed distinctive bands for IgM and IgG of both proteins (RBD and N) in positive samples. The sensitivity of RBD-based LFA was 70.9% and 39.8% for IgG and IgM, respectively, with a specificity of 100% for both. The N-based LFA exhibited a sensitivity of 73.8% and 35.9% for IgG and IgM, respectively, while its specificity was 75% and 100% for IgG and IgM, respectively. Our developed LFA could afford a tool for surveillance programs in low-resource countries. Moreover, it might be functional for rapid and inexpensive monitoring of the anti-SARS-CoV-2 antibodies in the sera of vaccinated individuals.

Generation and utility of a single-chain fragment variable monoclonal antibody platform against a baculovirus expressed recombinant receptor binding domain of SARS-CoV-2 spike protein

As the second wave of COVID-19 launched, various variants of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) have emerged with a dramatic global spread amongst millions of people causing unprecedented case fatalities and economic shut-downs. That initiated a necessity for developing specific diagnostics and therapeutics along with vaccines to control such a pandemic. This endeavor describes generation of murine derived recombinant single-chain fragment variable (scFv) as a monoclonal antibody (MAb) platform targeting the receptor binding domain (RBD) of Spike protein of SARS-CoV-2. A specific synthesized RBD coding sequence was cloned and expressed in Baculovirus expression system. The recombinant RBD (rRBD) was ascertained to be at the proper encoding size of ∼ 600bp and expressed protein of the molecular weight of ∼ 21KDa. Purified rRBD was proved genuinely antigenic and immunogenic, exhibiting specific reactivity to anti-SARS-CoV-2 antibody in an indirect enzyme-linked immunosorbent assay (ELISA), and inducing strong seroconversion in immunized mice. The scFv phage display library against rRBD was successfully constructed, revealing ∼ 90 % recombination frequency, and great enriching factor reaching 88 % and 25 % in polyclonal Ab-based and MAb-based ELISAs, respectively. Typically, three unique scFvs were generated, selected, purified and molecularly identified. That was manifested by their: accurate structure, close relation to the mouse immunoglobulin (Ig) superfamily, right anchored six complementarily-determining regions (CDRs) as three within variable heavy (vH) and variable light (vL) regions each, and proper configuration of the three-dimensional (3D) structure. Besides, their expression downstream in a non-suppressive amber codon of E. coli strain SS32 created a distinct protein band at an apparent molecular weight of ∼ 27KDa. Moreover, the purified scFvs showed authentic immunoreactivity and specificity to both rRBD and SARS-CoV-2 in western blot and ELISA. Accordingly, these developed scFvs platform might be a functional candidate for research, inexpensive diagnostics and therapeutics, mitigating spread of COVID-19.

Removal of 3C protease from the 3ABC improves expression, solubility, and purification of the recombinant 3AB of foot-and-mouth disease virus

During an ongoing outbreak of Foot-and-Mouth Disease Virus (FMDV), it is crucial to distinguish naturally infected from vaccinated seropositive animals. This would support clinical assessment and punctual vigilance. Assays based on 3ABC non-structural protein as an antigen are reliable for this intention. However, the insolubility and degradation of recombinant 3ABC during expression and purification are serious challenges. In this study, alternatively to expressing the recombinant 3ABC (r3ABC), we expressed the 3AB coding sequence (~672 bp) as a recombinant protein (r3AB) with a molecular mass of ~26 KDa. Analytical data from three-dimensional structure, hydrophilicity, and antigenic properties for 3ABC and 3AB exhibited the 3C protein as a hydrophobic, while 3AB as a hydrophilic and highly antigenic protein. The expressed r3AB was recovered as a completely soluble matter after merely native purification, unlike the full expressed r3ABC. Immunoreactivity of r3AB to anti-FMDV antibody in infected sera with different FMDV serotypes was confirmed by the western blot and indirect ELISA. Besides, the authentic antigenicity of purified r3AB was demonstrated through its ability to induce specific seroconversion in mice. Summarily, the removal of 3C: has influenced neither 3D structure nor antigenic properties of the purified r3AB, overcame insolubility and degradation of the r3ABC, and generated a potential superior antigen (r3AB) for herd screening of animals to any FMDV serotype.

Utilization of a recombinant defensin from Maize (Zea mays L.) as a potential antimicrobial peptide

The search for effective and bioactive antimicrobial molecules to  encounter the medical need for new antibiotics is an encouraging area of research. Plant defensins are small cationic, cysteine-rich peptides with a stabilized tertiary structure by disulfide-bridges and characterized by a wide range of biological functions. The heterologous expression of Egyptian maize defensin (MzDef) in Escherichia coli and subsequent purification by glutathione affinity chromatography yielded 2 mg/L of recombinant defensin peptide. The glutathione-S-transferase (GST)-tagged MzDef of approximately 30 kDa in size (26 KDa GST +  ~ 4 KDa MzDef peptide) was immunodetected with anti-GST antibodies. The GST-tag was successfully cleaved from the MzDef peptide by thrombin, and the removal was validated by the Tris-Tricine gel electrophoresis. The MzDef induced strong growth inhibition of Rhizoctonia solani, Fusarium verticillioides, and Aspergillus niger by 94.23%, 93.34%, and 86.25%, respectively, whereas relatively weak growth inhibitory activity of 35.42% against Fusarium solani was recorded. Moreover, strong antibacterial activities were demonstrated against E. coli and Bacillus cereus and the moderate activities against Salmonella enterica and Staphylococcus aureus at all tested concentrations (0.1, 0.2, 0.4, 0.8, 1.6, and 3.2 µM). Furthermore, the in vitro MTT assay exhibited promising anticancer activity against all tested cell lines (hepatocellular carcinoma, mammary gland breast cancer, and colorectal carcinoma colon cancer) with IC50 values ranging from 14.85 to 29.85 µg/mL. These results suggest that the recombinant peptide MzDef may serve as a potential alternative antimicrobial and anticancer agent to be used in medicinal application.

Characterization, cloning, expression and bioassay of vip3 gene isolated from an Egyptian Bacillus thuringiensis against whiteflies

Throughout the vegetative life of Bacillus thuringiensis, vegetative insecticidal proteins (Vip) are produced and secreted. In the present study, the vip3 gene isolated from Bacillus thuringiensis, an Egyptian isolate, was successfully amplified (2.4 kbp) and expressed using bacterial expression system. The molecular mass of the expressed protein was verified using SDS-PAGE and western blot analysis. Whiteflies were also screened for susceptibility to the expressed Vip3 protein (LC50). In addition, ST50 was determined to assess the kill speed of the expressed Vip3 protein against whiteflies compared to the whole vegetative proteins. The results showed that the potency of whole B. thuringiensis vegetative proteins against whiteflies was slightly higher than the expressed Vip3 protein with 4.7-fold based on LC50 value. However, the ST50 parameter showed no significant difference between both the B. thuringiensis vegetative proteins and the expressed Vip3 alone. The results showed that the vip3 gene was successfully expressed in an active form which showed high susceptibility to whiteflies based on the virulence parameters LC50 and ST50. To our knowledge, this study showed for the first time the high toxicity of the expressed Vip3 proteins of B. thuringiensis toward whiteflies as a hopeful and promising bio-control agent.

Expression of 1B capsid protein of Foot-and-mouth disease virus (FMDV) using baculovirus expression system and its validation in detecting SAT 2- specific antisera

Foot-and-mouth disease virus (FMDV) is one of the most devastating animal viruses that affect livestock worldwide. The 1B capsid of FMDV has been widely used to detect and confirm the infection. In the present study, the sequence coding for 1B subunit of FMDV capsid was expressed in insect cells using the baculovirus expression system under the polyhedrin (polh) promoter. The expression of 1B capsid protein was validated in the culture filtrate of insect cells using SDS-PAGE and western blotting. The culture filtrate containing recombinant 1B capsid (r1B) was used as a coated antigen in an indirect enzyme-linked immunosorbent assay (ELISA). The antigenicity and specificity of r1B against SAT 2 serotype-specific antibodies were assessed. Our results revealed that a protein concentration as low as 25 ng could detect SAT 2-specific antibodies in ELISA. The results highlight the application of insect cells developed r1B protein in the detection of FMDV. Further studies are required to determine the ability of r1B to detect other FMDV serotypes.

Expressing the immunodominant projection domain of infectious bursal disease virus fused to the fragment crystallizable of chicken IgY in yellow maize for a prospective edible vaccine

Control of Infectious bursal disease virus (IBDV) in endemic countries has been based on early immunization of chicks using conventional live or inactivated vaccines that became not fully effectual and have biosafety concerns. This endeavor seeks generating a recombinant chimeric protein merging the projection domain (PD) of IBDV VP2 capsid with the fragment crystallizable (Fc) of avian IgY (FcIgY), in maize as a prospective poultry edible vaccine. The PD sequence was built on the basis of very virulent IBDV isolates circulating in Egypt. After optimization of codon-usage in maize, sequences of PD and FcIgY were effectively expressed in two elites of yellow maize via bombardment transformation in immature embryos. Chimeric protein amount in stable transgenic samples ranged from1.36% to 3.03% of the total soluble protein based on tissue age and maize cultivar. IBDV VP2 coding sequence was amplified from viral RNA, cloned, and expressed in E. coli. A group of Balb/C mice were hyper-immunized with purified recombinant VP2 protein for raising anti- recombinant VP2 antibodies (anti-rVP2 Ab). Proper expression in maize and immunoreactivity of the chimeric protein (PD-FcIgY) to chicken anti- IBDV and anti-rVP2 Ab were confirmed by both direct and indirect double antibody sandwich (DAS)-ELISAs as well as western blotting. Seeds of regenerated transgenic maize will be validated for chickens as edible vaccination in further studies.

Construction, Expression and Evaluation of Recombinant VP2 Protein for serotype-independent Detection of FMDV Seropositive Animals in Egypt

Foot-and-mouth disease virus (FMDV) is one of the most devastating viral pathogens of cloven-hoofed animals. The detection of antibodies (Ab) against FMDV structural proteins (SP) using virus neutralization test (VNT) and liquid-phase blocking ELISA (LPBE) is the standard procedure in use for monitoring seroconversion in animals post vaccination, the prevalence of infection-surveillance, proving clinical cases and seronegative status of FMDV-free/naïve-animals prior transportation. However, due to variations within SP of FMDV serotypes, each serotype-specific Ab should be detected separately which is laborious and time-consuming. Accordingly, it is crucial to develop a sensitive, rapid, and accurate test capable of detecting FMDV-specific Ab, regardless its serotype. This study describes the heterologous expression of VP2 protein in E. coli, and its evaluation as a capture antigen in a simple indirect ELISA for serotype-independent detection of anti-FMDV Ab. Sequence analysis revealed that the VP2-coding sequence is considerably conserved among FMDV serotypes. The recombinant VP2 (rVP2), a 22 kDa polypeptide, was purified to near homogeneity by affinity chromatography under native conditions. Immunoreactivity of the rVP2 was confirmed by using a panel of positive sera including sera from animals vaccinated with the local trivalent vaccine and guinea pig FMDV antiserum, which is routinely used as tracing/detecting Ab in LPBE testing. The results obtained from the VP2-based ELISA were comparable to those determined by VNT and LPBE standard diagnostic assays. Specificity and sensitivity of rVP2 in capturing anti-FMDV Ab were 98.3% and 100%, respectively. The developed VP2-ELISA is proved reliable and time-efficient assay for detection of FMDV seropositive animals, regardless the FMDV serotype that can be implemented in a combination with VNT and/or LPBE for rapid diagnosis of an ongoing FMDV infection.

Polyclonal antibodies against the recombinantly expressed coat protein of the Citrus psorosis virus

Psorosis is a damaging disease of citrus that is widespread in many parts of the world. Citrus psorosis virus (CPsV), the type species of the genus Ophiovirus, is the putative causal agent of psorosis. Detection of CPsV by laboratory methods, serology in particular is a primary requirement for large-scale surveys but their production has been impaired by the difficulty of obtaining sufficient clean antigen for immunization. Specific PAbs against coat protein were produced in E. coli using recombinant DNA approach. The full length CP gene fragment was amplified by RT-PCR using total RNA extracted from CPsV infected citrus leaves and CP specific primers. The obtained product (1320bp) was cloned, sequenced and sub-cloned into p^ET-30(+) expression vector. Expression was induced and screened in different bacterial clones by the presence of the expressed protein (48kDa) and optimized in one clone. Expressed CP was purified using batch chromatography under denaturing conditions. Specificity of expressed protein was demonstrated by ELISA before used as antigen for raising PAbs in mice. Specificity of the raised PAbs to CPsV was verified by ELISA and western blotting. The raised PAbs were showed highly effectiveness in screening by ELISA comparing with the commercial antibodies purchased from Agritest, Valanzano, Italy. The expression of CPsV CP gene in E. coli, production of PAbs using recombinant protein as an antigen, the suitability of these antibodies for use in immunodiagnostics against the CPsV Egyptian isolate have been accomplished in this work.