Assembly and Purification of Polyomavirus-Like Particles from Plants

Production and Purification of Virus-Like Particles by Transient Expression in Plants

Transient expression in plants has become a useful production system for virus-like particle (VLP) expression. High yields and flexible approaches to assembling complex VLPs, combine with ease of scale-up and inexpensive reagents to provide an attractive method for recombinant protein expression in general. Plants have demonstrated excellent capacity for the assembly and production of protein cages for use in vaccine design and nanotechnology. Furthermore, numerous virus structures have now been determined using plant-expressed VLPs, showing the utility of this approach in structural virology. Transient protein expression in plants uses common microbiology techniques, leading to a straightforward transformation procedure that does not result in stable transgenesis. In this chapter, we aim to provide a generic protocol for transient expression of VLPs in Nicotiana benthamiana using soil-free plant cultivation and a simple vacuum infiltration procedure, along with methodology for purifying VLPs from plant leaves.

Protein cargo encapsulation by virus‐like particles: Strategies and applications

Viruses and the recombinant protein cages assembled from their structural proteins, known as virus-like particles (VLPs), have gained wide interest as tools in biotechnology and nanotechnology. Detailed structural information and their amenability to genetic and chemical modification make them attractive systems for further engineering. This review describes the range of non-enveloped viruses that have been co-opted for heterologous protein cargo encapsulation and the strategies that have been developed to drive encapsulation. Spherical capsids of a range of sizes have been used as platforms for protein cargo encapsulation. Various approaches, based on native and non-native interactions between the cargo proteins and inner surface of VLP capsids, have been devised to drive encapsulation. Here, we outline the evolution of these approaches, discussing their benefits and limitations. Like the viruses from which they are derived, VLPs are of interest in both biomedical and materials applications. The encapsulation of protein cargo inside VLPs leads to numerous uses in both fundamental and applied biocatalysis and biomedicine, some of which are discussed herein. The applied science of protein-encapsulating VLPs is emerging as a research field with great potential. Developments in loading control, higher order assembly, and capsid optimization are poised to realize this potential in the near future. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

Protein Cages: From Fundamentals to Advanced Applications

Proteins that self-assemble into polyhedral shell-like structures are useful molecular containers both in nature and in the laboratory. Here we review efforts to repurpose diverse protein cages, including viral capsids, ferritins, bacterial microcompartments, and designed capsules, as vaccines, drug delivery vehicles, targeted imaging agents, nanoreactors, templates for controlled materials synthesis, building blocks for higher-order architectures, and more. A deep understanding of the principles underlying the construction, function, and evolution of natural systems has been key to tailoring selective cargo encapsulation and interactions with both biological systems and synthetic materials through protein engineering and directed evolution. The ability to adapt and design increasingly sophisticated capsid structures and functions stands to benefit the fields of catalysis, materials science, and medicine.

Artificial Self-assembling Nanocompartment for Organizing Metabolic Pathways in Yeast

Metabolic pathways are commonly organized by sequestration into discrete cellular compartments. Compartments prevent unfavorable interactions with other pathways and provide local environments conducive to the activity of encapsulated enzymes. Such compartments are also useful synthetic biology tools for examining enzyme/pathway behavior and for metabolic engineering. Here, we expand the intracellular compartmentalization toolbox for budding yeast (Saccharomyces cerevisiae) with Murine polyomavirus virus-like particles (MPyV VLPs). The MPyV system has two components: VP1 which self-assembles into the compartment shell and a short anchor, VP2C, which mediates cargo protein encapsulation via binding to the inner surface of the VP1 shell. Destabilized green fluorescent protein (GFP) fused to VP2C was specifically sorted into VLPs and thereby protected from host-mediated degradation. An engineered VP1 variant displayed improved cargo capture properties and differential subcellular localization compared to wild-type VP1. To demonstrate their ability to function as a metabolic compartment, MPyV VLPs were used to encapsulate myo-inositol oxygenase (MIOX), an unstable and rate-limiting enzyme in d-glucaric acid biosynthesis. Strains with encapsulated MIOX produced ∼20% more d-glucaric acid compared to controls expressing "free" MIOX─despite accumulating dramatically less expressed protein─and also grew to higher cell densities. This is the first demonstration in yeast of an artificial biocatalytic compartment that can participate in a metabolic pathway and establishes the MPyV platform as a promising synthetic biology tool for yeast engineering.

Development of diagnostic tools for IBDV detection using plants as bioreactors

Infectious bursal disease virus (IBDV) is the etiological agent of an immunosuppressive and highly contagious disease that affects young birds, thus causing important economic losses in the poultry industry. Multimeric particles with different architectures based on the capsid protein VP2 have been widely produced for different purposes. We hereby show the production and easy recovery of IBDV subviral particles (SVP) from transiently transformed Nicotiana benthamiana. The SVP, which were observed by electronic microscopy, proved to be antigenically and immunogenically similar to the virion. Indeed, anti-IBDV antibodies from samples of infected birds recognized these SVP and, when injected intramuscularly, these subviral particles also evoked a humoral immune response in chickens. We developed an in-house ELISA using SVP as coating reagent that demonstrated to be highly accurate and in good agreement with a commercial ELISA. This study demonstrates that the recombinant antigen generated and the technology used to produce it are suitable for developing a diagnostic tool against Infectious bursal disease.

Virus-Derived Nanoparticles

Capsid-based virus particles are widely engineered as viral nanoparticles and virus-like nanoparticles. The highly organized and uniform capsid structures make them ideal candidates for both in vitro and in vivo applications such as therapeutic delivery vehicles or enzymatic nanoreactors. Viruses have adapted to naturally infect a wide variety of organisms making their production achievable in various expression systems from bacterial to plants. Viral capsids can be modified externally and internally to suit the final application. The wide range of possible applications, ease of production in the system of choice, and customizable modification of viral capsids makes them an attractive choice in the field of nanotechnology. In this chapter we aim to provide a generic protocol for the purification and characterization of virus-derived nanoparticles and methodology for chemically labelling them to monitor their uptake in mammalian cells.

Programmable In Vitro Coencapsidation of Guest Proteins for Intracellular Delivery by Virus-like Particles

Bioinspired self-sorting and self-assembling systems using engineered versions of natural protein cages are being developed for biocatalysis and therapeutic delivery. The packaging and intracellular delivery of guest proteins is of particular interest for both in vitro and in vivo cell engineering. However, there is a lack of bionanotechnology platforms that combine programmable guest protein encapsidation with efficient intracellular uptake. We report a minimal peptide anchor for in vivo self-sorting of cargo-linked capsomeres of murine polyomavirus (MPyV) that enables controlled encapsidation of guest proteins by in vitro self-assembly. Using Förster resonance energy transfer, we demonstrate the flexibility in this system to support coencapsidation of multiple proteins. Complementing these ensemble measurements with single-particle analysis by super-resolution microscopy shows that the stochastic nature of coencapsidation is an overriding principle. This has implications for the design and deployment of both native and engineered self-sorting encapsulation systems and for the assembly of infectious virions. Taking advantage of the encoded affinity for sialic acids ubiquitously displayed on the surface of mammalian cells, we demonstrate the ability of self-assembled MPyV virus-like particles to mediate efficient delivery of guest proteins to the cytosol of primary human cells. This platform for programmable coencapsidation and efficient cytosolic delivery of complementary biomolecules therefore has enormous potential in cell engineering.

Purification of virus-like particles (VLPs) expressed in the silkworm Bombyx mori

Virus-like particles (VLPs) are a promising and developing option for vaccination and gene therapy. They are also interesting as shuttles for drug targeting. Currently, several different gene expression systems are available, among which the silkworm expression system is known for its mass production capacity. However, cost-effective purification with high purity of the target protein is a particular bottleneck for this system. The present review evaluates the advances in the purification of VLPs, especially from silkworm larval hemolymph. Beginning with applicable pre-treatments for VLPs over to chromatography methods and quality control of the purified VLPs. Whereupon the main focus is on the different chromatography approaches for the purification, but the structure of the VLPs and their intended use for humans make also the quality control important. Within this, the stability of the VLPs which has to be considered for the purification is as well discussed.

Nattokinase: An Oral Antithrombotic Agent for the Prevention of Cardiovascular Disease

Natto, a fermented soybean product, has been consumed as a traditional food in Japan for thousands of years. Nattokinase (NK), a potent blood-clot dissolving protein used for the treatment of cardiovascular diseases, is produced by the bacterium Bacillus subtilis during the fermentation of soybeans to produce Natto. NK has been extensively studied in Japan, Korea, and China. Recently, the fibrinolytic (anti-clotting) capacity of NK has been recognized by Western medicine. The National Science Foundation in the United States has investigated and evaluated the safety of NK. NK is currently undergoing a clinical trial study (Phase II) in the USA for atherothrombotic prevention. Multiple NK genes have been cloned, characterized, and produced in various expression system studies. Recombinant technology represents a promising approach for the production of NK with high purity for its use in antithrombotic applications. This review covers the history, benefit, safety, and production of NK. Opportunities for utilizing plant systems for the large-scale production of NK, or for the production of edible plants that can be used to provide oral delivery of NK without extraction and purification are also discussed.

Production of Human papillomavirus pseudovirions in plants and their use in pseudovirion-based neutralisation assays in mammalian cells

Human papillomaviruses (HPV) cause cervical cancer and have recently also been implicated in mouth, laryngeal and anogenital cancers. There are three commercially available prophylactic vaccines that show good efficacy; however, efforts to develop second-generation vaccines that are more affordable, stable and elicit a wider spectrum of cross-neutralising immunity are still ongoing. Testing antisera elicited by current and candidate HPV vaccines for neutralizing antibodies is done using a HPV pseudovirion (PsV)-based neutralisation assay (PBNA). PsVs are produced by transfection of mammalian cell cultures with plasmids expressing L1 and L2 capsid proteins, and a reporter gene plasmid, a highly expensive process. We investigated making HPV-16 PsVs in plants, in order to develop a cheaper alternative. The secreted embryonic alkaline phosphatase (SEAP) reporter gene and promoter were cloned into a geminivirus-derived plant expression vector, in order to produce circular dsDNA replicons. This was co-introduced into Nicotiana benthamiana plants with vectors expressing L1 and L2 via agroinfiltration, and presumptive PsVs were purified. The PsVs contained DNA, and could be successfully used for PBNA with anti-HPV antibodies. This is the first demonstration of the production of mammalian pseudovirions in plants, and the first demonstration of the potential of plants to make DNA vaccines.

Plants as Factories for Human Pharmaceuticals: Applications and Challenges

Plant molecular farming (PMF), defined as the practice of using plants to produce human therapeutic proteins, has received worldwide interest. PMF has grown and advanced considerably over the past two decades. A number of therapeutic proteins have been produced in plants, some of which have been through pre-clinical or clinical trials and are close to commercialization. Plants have the potential to mass-produce pharmaceutical products with less cost than traditional methods. Tobacco-derived antibodies have been tested and used to combat the Ebola outbreak in Africa. Genetically engineered immunoadhesin (DPP4-Fc) produced in green plants has been shown to be able to bind to MERS-CoV (Middle East Respiratory Syndrome), preventing the virus from infecting lung cells. Biosafety concerns (such as pollen contamination and immunogenicity of plant-specific glycans) and costly downstream extraction and purification requirements, however, have hampered PMF production from moving from the laboratory to industrial application. In this review, the challenges and opportunities of PMF are discussed. Topics addressed include; transformation and expression systems, plant bioreactors, safety concerns, and various opportunities to produce topical applications and health supplements.