Natural supramolecular building blocks. Wild-type cowpea mosaic virus

Immunogenicity of novel vB_EcoS_NBD2 bacteriophage-originated nanotubes as a carrier for peptide-based vaccines

Non-infectious virus-like nanoparticles mimic native virus structures and can be modified by inserting foreign protein fragments, making them immunogenic tools for antigen presentation. This study investigated, for the first time, the immunogenicity of long and flexible polytubes formed by yeast-expressed tail tube protein gp39 of bacteriophage vB_EcoS_NBD2 and evaluated their ability to elicit an immune response against the inserted protein fragments. Protein gp39-based polytubes induced humoral immune response in mice, even without the use of adjuvant. Bioinformatics analysis guided the selection of protein fragments from Acinetobacter baumannii for insertion into the C-terminus of gp39. Chimeric polytubes, displaying 28-amino acid long OmpA protein fragment, induced IgG response against OmpA protein fragment in immunized mice. These polytubes demonstrated their effectiveness both as antigen carrier and an adjuvant, when the OmpA fragments were either displayed on chimeric polytubes or used alongside with the unmodified polytubes. Our findings expand the potential applications of long and flexible polytubes, contributing to the development of novel antigen carriers with improved immunogenicity and antigen presentation capabilities.

Pharmacology of a Plant Virus Immunotherapy Candidate for Peritoneal Metastatic Ovarian Cancer

Due to the increasing incidence of cancer, there is a need to develop new platforms that can combat this disease. Cancer immunotherapy is a platform that takes advantage of the immune system to recognize and eradicate tumors and metastases. Our lab has identified a plant virus nanoparticle, cowpea mosaic virus (CPMV) as a promising approach for cancer immunotherapy. When administered intratumorally, CPMV relieves the immune system of tumor-induced immunosuppression and reprograms the tumor microenvironment into an activated state to launch systemic antitumor immunity. The efficacy of CPMV has been tested in many tumor models and in canine cancer patients with promising results: tumor shrinkage, systemic efficacy (abscopal effect), and immune memory to prevent recurrence. To translate this drug candidate from the bench to the clinic, studies that investigate the safety, pharmacology, and toxicity are needed. In this work, we describe the efficacy of CPMV against a metastatic ovarian tumor model and investigate the biodistribution of CPMV after single or repeated intraperitoneal administration in tumor-bearing and healthy mice. CPMV shows good retention in the tumor nodules and broad bioavailability with no apparent organ toxicity based on histopathology. Data indicate persistence of the viral RNA, which remains detectable 2 weeks post final administration, a phenomenon also observed with some mammalian viral infections. Lastly, while protein was not detected in stool or urine, RNA was shed through excretion from mice; however, there was no evidence that RNA was infectious to plants. Taken together, the data indicate that systemic administration results in broad bioavailability with no apparent toxicity. While RNA is shed from the subjects, data suggest agronomical safety. This data is consistent with prior reports and provides support for translational efforts.

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.

The Plant Viruses and Molecular Farming: How Beneficial They Might Be for Human and Animal Health?

Plant viruses have traditionally been studied as pathogens in the context of understanding the molecular and cellular mechanisms of a particular disease affecting crops. In recent years, viruses have emerged as a new alternative for producing biological nanomaterials and chimeric vaccines. Plant viruses were also used to generate highly efficient expression vectors, revolutionizing plant molecular farming (PMF). Several biological products, including recombinant vaccines, monoclonal antibodies, diagnostic reagents, and other pharmaceutical products produced in plants, have passed their clinical trials and are in their market implementation stage. PMF offers opportunities for fast, adaptive, and low-cost technology to meet ever-growing and critical global health needs. In this review, we summarized the advancements in the virus-like particles-based (VLPs-based) nanotechnologies and the role they played in the production of advanced vaccines, drugs, diagnostic bio-nanomaterials, and other bioactive cargos. We also highlighted various applications and advantages plant-produced vaccines have and their relevance for treating human and animal illnesses. Furthermore, we summarized the plant-based biologics that have passed through clinical trials, the unique challenges they faced, and the challenges they will face to qualify, become available, and succeed on the market.

Surface decorated reporter-tagged chikungunya virus-like particles for clinical diagnostics and identification of virus entry inhibitors

The ever-evolving and versatile VLP technology is becoming an increasingly popular area of science. This study presents surface decorated reporter-tagged VLPs of CHIKV, an enveloped RNA virus of the genus alphavirus and its applications. Western blot, IFA and live-cell imaging confirm the expression of reporter-tagged CHIK-VLPs from transfected HEK293Ts. CryoEM micrographs reveal particle diameter as ∼67nm and 56-70 nm, respectively, for NLuc CHIK-VLPs and mCherry CHIK-VLPs. Our study demonstrates that by exploiting NLuc CHIK-VLPs as a detector probe, robust ratiometric luminescence signal in CHIKV-positive sera compared to healthy controls can be achieved swiftly. Moreover, the potential activity of the Suramin drug as a CHIKV entry inhibitor has been validated through the reporter-tagged CHIK-VLPs. The results reported in this study open new avenues in the eVLPs domain and offer potential for large-scale screening of clinical samples and antiviral agents targeting entry of CHIKV and other alphaviruses.

Direct measurement of Stokes-Einstein diffusion of Cowpea mosaic virus with 19 µs-resolved XPCS

Brownian motion of Cowpea mosaic virus (CPMV) in water was measured using small-angle X-ray photon correlation spectroscopy (SA-XPCS) at 19.2 µs time resolution. It was found that the decorrelation time τ(Q) = 1/DQ² up to Q = 0.091 nm^-1. The hydrodynamic radius R_H determined from XPCS using Stokes-Einstein diffusion D = kT/(6πηR_H) is 43% larger than the geometric radius R₀ determined from SAXS in the 0.007 M K₃PO₄ buffer solution, whereas it is 80% larger for CPMV in 0.5 M NaCl and 104% larger in 0.5 M (NH₄)₂SO₄, a possible effect of aggregation as well as slight variation of the structures of the capsid resulting from the salt-protein interactions.

Applications of Charge Detection Mass Spectrometry in Molecular Biology and Biotechnology

Charge detection mass spectrometry (CDMS) is a single-particle technique where the masses of individual ions are determined from simultaneous measurement of their mass-to-charge ratio (m/z) and charge. Masses are determined for thousands of individual ions, and then the results are binned to give a mass spectrum. Using this approach, accurate mass distributions can be measured for heterogeneous and high-molecular-weight samples that are usually not amenable to analysis by conventional mass spectrometry. Recent applications include heavily glycosylated proteins, protein complexes, protein aggregates such as amyloid fibers, infectious viruses, gene therapies, vaccines, and vesicles such as exosomes.

Protein Nanoparticles: Uniting the Power of Proteins with Engineering Design Approaches

Protein nanoparticles, PNPs, have played a long-standing role in food and industrial applications. More recently, their potential in nanomedicine has been more widely pursued. This review summarizes recent trends related to the preparation, application, and chemical construction of nanoparticles that use proteins as major building blocks. A particular focus has been given to emerging trends related to applications in nanomedicine, an area of research where PNPs are poised for major breakthroughs as drug delivery carriers, particle-based therapeutics or for non-viral gene therapy.

Bioconjugation of Active Ingredients to Plant Viral Nanoparticles Is Enhanced by Preincubation with a Pluronic F127 Polymer Scaffold

Proteinaceous nanoparticles can be used to deliver large payloads of active ingredients, which is advantageous in medicine and agriculture. However, the conjugation of hydrophobic ligands to hydrophilic nanocarriers such as plant viral nanoparticles (plant VNPs) can result in aggregation by reducing overall solubility. Given the benefits of hydrophilic nanocarrier platforms for targeted delivery and multivalent ligand display, coupled with the versatility of hydrophobic drugs, contrast agents, and peptides, this is an issue that must be addressed to realize their full potential. Here, we report two preincubation strategies that use a Pluronic F127 polymer scaffold to prevent the aggregation of conjugated plant VNPs: a plant VNP-polymer precoat (COAT) and an active ingredient formulation combined with a plant VNP-polymer precoat (FORMCOAT). The broad applications of these modified conjugation strategies were highlighted by testing their compatibility with three types of bioconjugation chemistry: N-hydroxysuccinimide ester-amine coupling, maleimide-thiol coupling, and copper(I)-catalyzed azide-alkyne cycloaddition (click chemistry). The COAT and FORMCOAT strategies promoted efficient bioconjugation and prevented the aggregation that accompanies conventional bioconjugation methods, thus improving the stability, homogeneity, and translational potential of plant VNP conjugates in medicine and agriculture.

Hydrophobic Cargo Encapsulation into Virus Protein Cages by Self-Assembly in an Aprotic Organic Solvent

While extensive studies of virus capsid assembly in environments mimicking in vivo conditions have led to an understanding of the thermodynamic driving forces at work, applying this knowledge to virus assembly in other solvents than aqueous buffers has not been attempted yet. In this study, Brome mosaic virus (BMV) capsid proteins were shown to preserve their self-assembly abilities in an aprotic polar solvent, dimethyl sulfoxide (DMSO). This facilitated protein cage encapsulation of nanoparticles and dye molecules that favor organic solvents, such as β-NaYF₄-based upconversion nanoparticles and BODIPY dye. Assembly was found to be robust relative to a surprisingly broad range of DMSO concentrations. Cargos with poor initial stability in aqueous solutions were readily encapsulated at high DMSO concentrations and then transferred to aqueous solvents, where they remained stable and preserved their function for months.

Viral Phrenology

We introduce Viral Phrenology, a new scheme for understanding the genomic composition of spherical viruses based on the locations of their structural protrusions. We used icosahedral point arrays to classify 135 distinct viral capsids collected from over 600 capsids available in the VIPERdb. Using gauge points of point arrays, we found 149 unique structural protrusions. We then show how to use the locations of these protrusions to determine the genetic composition of the virus. We then show that ssDNA, dsDNA, dsRNA and ssRNA viruses use different arrangements for distributing their protrusions. We also found that Triangulation number is also partially dependent on the structural protrusions. This analysis begins to tie together Baltimore Classification and Triangulation number using point arrays.

Modification of a Tumor-Targeting Bacteriophage for Potential Diagnostic Applications

BACKGROUND

Tumor-targeting bacteriophages can be used as a versatile new platform for the delivery of diagnostic imaging agents and therapeutic cargo. This became possible due to the development of viral capsid modification method. Earlier in our laboratory and using phage display technology, phages to malignant breast cancer cells MDA-MB 231 were obtained. The goal of this study was the optimization of phage modification and the assessment of the effect of the latter on the efficiency of phage particle penetration into MDA-MB 231 cells.

METHODS

In this work, we used several methods, such as chemical phage modification using FAM-NHS ester, spectrophotometry, phage amplification, sequencing, phage titration, flow cytometry, and confocal microscopy.

RESULTS

We performed chemical phage modification using different concentrations of FAM-NHS dye (0.5 mM, 1 mM, 2 mM, 4 mM, 8 mM). It was shown that with an increase of the modification degree, the phage titer decreases. The maximum modification coefficient of the phage envelope with the FAM-NHS dye was observed with 4 mM modifying agent and had approximately 804,2 FAM molecules per phage. Through the immunofluorescence staining and flow cytometry methods, it was shown that the modified bacteriophage retains the ability to internalize into MDA-MB-231 cells. The estimation of the number of phages that could have penetrated into one tumor cell was conducted.

CONCLUSIONS

Optimizing the conditions for phage modification can be an effective strategy for producing tumor-targeting diagnostic and therapeutic agents, i.e., theranostic drugs.

Subset of Fluorophores Is Responsible for Radiation Brightening in Viromimetic Particles

In certain conditions, dye-conjugated icosahedral virus shells exhibit suppression of concentration quenching. The recently observed radiation brightening at high fluorophore densities has been attributed to coherent emission, i.e., to a cooperative process occurring within a subset of the virus-supported fluorophores. Until now, the distribution of fluorophores among potential conjugation sites and the nature of the active subset remained unknown. With the help of mass spectrometry and molecular dynamics simulations, we found which conjugation sites in the brome mosaic virus capsid are accessible to fluorophores. Reactive external surface lysines but also those at the lumenal interface where the coat protein N-termini are located showed virtually unrestricted access to dyes. The third type of labeled lysines was situated at the intercapsomeric interfaces. Through limited proteolysis of flexible N-termini, it was determined that dyes bound to them are unlikely to be involved in the radiation brightening effect. At the same time, specific labeling of genetically inserted cysteines on the exterior capsid surface alone did not lead to radiation brightening. The results suggest that lysines situated within the more rigid structural part of the coat protein provide the chemical environments conducive to radiation brightening, and we discuss some of the characteristics of these environments.

Application of Plant Viruses in Biotechnology, Medicine, and Human Health

Plant-based nanotechnology programs using virus-like particles (VLPs) and virus nanoparticles (VNPs) are emerging platforms that are increasingly used for a variety of applications in biotechnology and medicine. Tobacco mosaic virus (TMV) and potato virus X (PVX), by virtue of having high aspect ratios, make ideal platforms for drug delivery. TMV and PVX both possess rod-shaped structures and single-stranded RNA genomes encapsidated by their respective capsid proteins and have shown great promise as drug delivery systems. Cowpea mosaic virus (CPMV) has an icosahedral structure, and thus brings unique benefits as a nanoparticle. The uses of these three plant viruses as either nanostructures or expression vectors for high value pharmaceutical proteins such as vaccines and antibodies are discussed extensively in the following review. In addition, the potential uses of geminiviruses in medical biotechnology are explored. The uses of these expression vectors in plant biotechnology applications are also discussed. Finally, in this review, we project future prospects for plant viruses in the fields of medicine, human health, prophylaxis, and therapy of human diseases.

In situ vaccine application of inactivated CPMV nanoparticles for cancer immunotherapy

Cowpea mosaic virus (CPMV) is currently in the development pipeline for multiple biomedical applications, including cancer immunotherapy. In particular the application of CPMV as in situ vaccine has shown promise; here the plant viral nanoparticle is used as an adjuvant and is injected directly into a tumor to reverse immunosuppression and prime systemic anti-tumor immunity. Efficacy of this CPMV-based cancer immunotherapy has been demonstrated in multiple tumor mouse models and canine cancer patients. However, while CPMV is non-infectious to mammals, it is infectious to legumes and therefore, from a safety perspective, it is desired to develop non-infectious CPMV formulations. Non-infectious virus-like particles of CPMV devoid of nucleic acids have been produced; nevertheless, efficacy of such empty CPMV nanoparticles does not match efficacy of nucleic acid-laden CPMV. The multivalent capsid activates the innate immune system through pathogen pattern recognition receptors (PRRs) such as toll-like receptors (TLRs); the RNA cargo provides additional signaling through TLR-7/8, which boosts the efficacy of this adjuvant. Therefore, in this study, we set out to develop RNA-laden, but non-infectious CPMV. We report inactivation of CPMV using UV light and chemical inactivation using β-propiolactone (βPL) or formalin. 7.5 J cm^-2 UV, 50 mM βPL or 1 mM formalin was determined to be sufficient to inactivate CPMV and prevented plant infection. We compared the immunogenicity of native CPMV and inactivated CPMV formulations in vitro and in vivo using RAW-Blue™ reporter cells and a murine syngeneic, orthotropic melanoma model (using B16F10 cells and C57BL6 mice). While the in vitro assay indicated activation of the RAW-Blue™ reporter cells by formaldehyde and UV-inactivated CPMV at levels comparable to native CPMV; βPL-inactivated CPMV appeared to have diminished activity. Tumor mouse model experiments indicate potent efficacy of the chemically-inactivated CPMV (UV-treated CPMV was not tested) leading to tumor regression and increased survival; efficacy was somewhat reduced when compared to CPMV, however these samples outperformed the empty CPMV nanoparticles. These results will facilitate the translational development of safe and potent CPMV-based cancer immunotherapies.

Self-assembled Viral Nanoparticles as Targeted Anticancer Vehicles

Viral nanoparticles (VNPs) comprise a variety of mammalian viruses, plant viruses, and bacteriophages, that have been adopted as building blocks and supra-molecular templates in nanotechnology. VNPs demonstrate the dynamic, monodisperse, polyvalent, and symmetrical architectures which represent examples of such biological templates. These programmable scaffolds have been exploited for genetic and chemical manipulation for displaying of targeted moieties together with encapsulation of various payloads for diagnosis or therapeutic intervention. The drug delivery system based on VNPs offer diverse advantages over synthetic nanoparticles, including biocompatibility, biodegradability, water solubility, and high uptake capability. Here we summarize the recent progress of VNPs especially as targeted anticancer vehicles from the encapsulation and surface modification mechanisms, involved viruses and VNPs, to their application potentials.

Inorganic-organic Nanomaterials for Therapeutics and Molecular Imaging Applications

Background::

Surface modification of nanoparticles with targeting moieties can be achieved through bioconjugation chemistries to impart new Functionalities. Various polymeric nanoparticles have been used for the formulation of nanoparticles such as naturally-occurring protein cages, virus-like particles, polymeric saccharides, and liposomes. These polymers have been proven to be biocompatible, side effects free and degradable with no toxicity.

Objectives::

This paper reviews available literature on the nanoparticles pharmaceutical and medical applications. The review highlights and updates the customized solutions for selective drug delivery systems that allow high-affinity binding between nanoparticles and the target receptors.

Methods::

Bibliographic databases and web-search engines were used to retrieve studies that assessed the usability of nanoparticles in the pharmaceutical and medical fields. Data were extracted on each system in vivo and in vitro applications, its advantages and disadvantages, and its ability to be chemically and genetically modified to impart new functionalities. Finally, a comparison between naturally occurring and their synthetic counterparts was carried out.

Results::

The results showed that nanoparticles-based systems could have promising applications in diagnostics, cell labeling, contrast agents (Magnetic Resonance Imaging and Computed Tomography), antimicrobial agents, and as drug delivery systems. However, precautions should be taken to avoid or minimize toxic effect or incompatibility of nanoparticles-based systems with the biological systems in case of pharmaceutical or medical applications.

Conclusion::

This review presented a summary of recent developments in the field of pharmaceutical nanotechnology and highlighted the challenges and the merits that some of the nanoparticles- based systems both in vivo and in vitro systems.

Biomimicked and CPMV-Imprinted Hollow Porous Zinc Phosphate Nanocapsules and Their Therapeutic Efficiency

Hollow zinc phosphate nanocapsules (hZPNCs) are an alloplastic biomaterial that has been synthesized to deliver chemotherapeutic drugs in a sustained manner. A very simple one-pot synthesis approach has been employed to synthesize hZPNCs by using cowpea mosaic virus (CPMV) in the presence of phosphate buffer (PBS) (0.01 M PBS, pH ∼7.2) with zinc acetate precursor. The synthesis mechanism of hZPNCs relies on the basis of biomineralization, where the precursor molecules initiate mineralization with the help of amino acid residues present on the CPMV capsid. The synthesized hollow nanocapsules were of diameter ∼50-60 nm and porous shell with thickness of ∼4 nm. The cavity performed as a reservoir for the anticancer drugs (DOX and IM). The release kinetic studies show the positive aspect of hZPNCs to be labeled as drug delivery cargo for sustained delivery. In vitro cytotoxic studies of hZPNCs and hZPNCs-chemo drugs on HEK293, HEPG2, and K562 cells were performed. The cytotoxic studies show that hZPNCs-DOX and hZPNCs-IM arrest the cell cycle of carcinoma cells (HEPG2 and K562 cells) at relatively low IC₅₀ and that the inhibition efficiency is dosage dependent. Furthermore, through HRTEM, in vitro cellular interactions of carcinoma cells with hZPNCs and chemo drug-loaded hZPNCs were confirmed by the cryo-sectioning of cells before and after the incubation. These studies revealed the likely endocytic pathway for the nanocapsules entering the cell and executing the specific action of delivering the anticancer drugs. Together, these results reveal the hZPNCs as potential sustained drug delivery agents.

Active Microneedle Administration of Plant Virus Nanoparticles for Cancer in situ Vaccination Improves Immunotherapeutic Efficacy

The solid tumor microenvironment (TME) poses a significant structural and biochemical barrier to immunotherapeutic agents. To address the limitations of tumor penetration and distribution, and to enhance antitumor efficacy of immunotherapeutics, we present here an autonomous active microneedle (MN) system for the direct intratumoral (IT) delivery of a potent immunoadjuvant, cowpea mosaic virus nanoparticles (CPMV) in vivo. In this active delivery system, magnesium (Mg) microparticles embedded into active MNs react with the interstitial fluid in the TME, generating a propulsive force to drive the nanoparticle payload into the tumor. Active delivery of CPMV payload into B16F10 melanomas in vivo demonstrated substantially more pronounced tumor regression and prolonged survival of tumor-bearing mice compared to that of passive MNs and conventional needle injection. Active MN administration of CPMV also enhanced local innate and systemic adaptive antitumor immunity. Our approach represents an elaboration of conventional CPMV in situ vaccination, highlighting substantial immune-mediated antitumor effects and improved therapeutic efficacy that can be achieved through an active and autonomous delivery system-mediated CPMV in situ vaccination.

Interaction Between Virus-Like Particles (VLPs) and Pattern Recognition Receptors (PRRs) From Dendritic Cells (DCs): Toward Better Engineering of VLPs

Virus-like particles (VLPs) have been shown to be strong activators of dendritic cells (DCs). DCs are the most potent antigen presenting cells (APCs) and their activation prompts the priming of immunity mediators based on B and T cells. The first step for the activation of DCs is the binding of VLPs to pattern recognition receptors (PRRs) on the surface of DCs, followed by VLP internalization. Like wild-type viruses, VLPs use specific PRRs from the DC; however, these recognition interactions between VLPs and PRRs from DCs have not been thoroughly reviewed. In this review, we focused on the interaction between proteins that form VLPs and PRRs from DCs. Several proteins that form VLP contain glycosylations that allow the direct interaction with PRRs sensing carbohydrates, prompting DC maturation and leading to the development of strong adaptive immune responses. We also discussed how the knowledge of the molecular interaction between VLPs and PRRs from DCs can lead to the smart design of VLPs, whether based on the fusion of foreign epitopes or their chemical conjugation, as well as other modifications that have been shown to induce a stronger adaptive immune response and protection against infectious pathogens of importance in human and veterinary medicine. Finally, we address the use of VLPs as tools against cancer and allergic diseases.

Unveiling the Hidden Rules of Spherical Viruses Using Point Arrays

Since its introduction, the Triangulation number has been the most successful and ubiquitous scheme for classifying spherical viruses. However, despite its many successes, it fails to describe the relative angular orientations of proteins, as well as their radial mass distribution within the capsid. It also fails to provide any critical insight into sites of stability, modifications or possible mutations. We show how classifying spherical viruses using icosahedral point arrays, introduced by Keef and Twarock, unveils new geometric rules and constraints for understanding virus stability and key locations for exterior and interior modifications. We present a modified fitness measure which classifies viruses in an unambiguous and rigorous manner, irrespective of local surface chemistry, steric hinderance, solvent accessibility or Triangulation number. We then use these point arrays to explain the immutable surface loops of bacteriophage MS2, the relative reactivity of surface lysine residues in CPMV and the non-quasi-equivalent flexibility of the HBV dimers. We then explain how point arrays can be used as a predictive tool for site-directed modifications of capsids. This success builds on our previous work showing that viruses place their protruding features along the great circles of the asymmetric unit, demonstrating that viruses indeed adhere to these geometric constraints.

Determination of Antibody Population Distributions for Virus-Antibody Conjugates by Charge Detection Mass Spectrometry

Virus-like particle (VLP) conjugates are being developed for biomedical applications; however, there is a lack of quantitative analytical methods to measure the extent of conjugation and modification of VLP based therapeutics. Charge detection mass spectrometry (CDMS) can measure mass distributions for large and heterogeneous complexes and is emerging as a valuable tool in the analysis of biologics. In this study, CDMS is used to characterize the stoichiometry and population distribution of antibodies covalently conjugated to the surface of a bacteriophage MS2 VLP. Initial CDMS analysis of the unconjugated MS2 particles suggested that they had packaged a broad distribution of exogenous genomic material. We developed procedures to remove the undesired genomic material from the VLP preparation and observed that, for the samples where the genomic fragments were removed, the antibody coupling reaction efficiency increased by almost a factor of 2. This meant there were (1) fewer VLPs with no antibodies bound, which is an important consideration for the efficacy of a targeted therapeutic and (2) fewer antibodies were wasted during the coupling reaction. CDMS could be employed in a similar manner as a tool to characterize coupling reaction product distributions and precursors and help inform the development of the next generation of conjugate-based therapies.

Virus-like particle size and molecular weight/mass determination applying gas-phase electrophoresis (native nES GEMMA)

(Bio-)nanoparticle analysis employing a nano-electrospray gas-phase electrophoretic mobility molecular analyzer (native nES GEMMA) also known as nES differential mobility analyzer (nES DMA) is based on surface-dry analyte separation at ambient pressure. Based on electrophoretic principles, single-charged nanoparticles are separated according to their electrophoretic mobility diameter (EMD) corresponding to the particle size for spherical analytes. Subsequently, it is possible to correlate the (bio-)nanoparticle EMDs to their molecular weight (M_W) yielding a corresponding fitted curve for an investigated analyte class. Based on such a correlation, (bio-)nanoparticle M_W determination via its EMD within one analyte class is possible. Turning our attention to icosahedral, non-enveloped virus-like particles (VLPs), proteinaceous shells, we set up an EMD/M_W correlation. We employed native electrospray ionization mass spectrometry (native ESI MS) to obtain M_W values of investigated analytes, where possible, after extensive purification. We experienced difficulties in native ESI MS with time-of-flight (ToF) detection to determine M_W due to sample inherent characteristics, which was not the case for charge detection (CDMS). nES GEMMA exceeds CDMS in speed of analysis and is likewise less dependent on sample purity and homogeneity. Hence, gas-phase electrophoresis yields calculated M_W values in good approximation even when charge resolution was not obtained in native ESI ToF MS. Therefore, both methods-native nES GEMMA-based M_W determination via an analyte class inherent EMD/M_W correlation and native ESI MS-in the end relate (bio-)nanoparticle M_W values. However, they differ significantly in, e.g., ease of instrument operation, sample and analyte handling, or costs of instrumentation.

Plant/Bacterial Virus-Based Drug Discovery, Drug Delivery, and Therapeutics

Viruses have recently emerged as promising nanomaterials for biotechnological applications. One of the most important applications of viruses is phage display, which has already been employed to identify a broad range of potential therapeutic peptides and antibodies, as well as other biotechnologically relevant polypeptides (including protease inhibitors, minimizing proteins, and cell/organ targeting peptides). Additionally, their high stability, easily modifiable surface, and enormous diversity in shape and size, distinguish viruses from synthetic nanocarriers used for drug delivery. Indeed, several plant and bacterial viruses (e.g., phages) have been investigated and applied as drug carriers. The ability to remove the genetic material within the capsids of some plant viruses and phages produces empty viral-like particles that are replication-deficient and can be loaded with therapeutic agents. This review summarizes the current applications of plant viruses and phages in drug discovery and as drug delivery systems and includes a discussion of the present status of virus-based materials in clinical research, alongside the observed challenges and opportunities.

Cowpea mosaic virus nanoparticles for cancer imaging and therapy

Nanoparticle platforms are particularly attractive for theranostic applications due to their capacity for multifunctionality and multivalency. Some of the most promising nano-scale scaffold systems have been co-opted from nature including plant viruses such as cowpea mosaic virus (CPMV). The use of plant viruses like CPMV as viral nanoparticles is advantageous for many reasons; they are non-infectious and nontoxic to humans and safe for use in intravital imaging and drug delivery. The CPMV capsid icosahedral shape allows for enhanced multifunctional group display and the ability to carry specific cargoes. The native tropism of CPMV for cell-surface displayed vimentin and the enhanced permeability and retention effect allow them to preferentially extravasate from tumor neovasculature and efficiently penetrate tumors. Furthermore, CPMVs can be engineered via several straightforward chemistries to display targeting and imaging moieties on external, addressable residues and they can be loaded internally with therapeutic drug cargoes. These qualities make them highly effective as biocompatible platforms for tumor targeting, intravital imaging and cancer therapy.

Small, Smaller, Nano: New Applications for Potato Virus X in Nanotechnology

Nanotechnology is an expanding interdisciplinary field concerning the development and application of nanostructured materials derived from inorganic compounds or organic polymers and peptides. Among these latter materials, proteinaceous plant virus nanoparticles have emerged as a key platform for the introduction of tailored functionalities by genetic engineering and conjugation chemistry. Tobacco mosaic virus and Cowpea mosaic virus have already been developed for bioimaging, vaccination and electronics applications, but the flexible and filamentous Potato virus X (PVX) has received comparatively little attention. The filamentous structure of PVX particles allows them to carry large payloads, which are advantageous for applications such as biomedical imaging in which multi-functional scaffolds with a high aspect ratio are required. In this context, PVX achieves superior tumor homing and retention properties compared to spherical nanoparticles. Because PVX is a protein-based nanoparticle, its unique functional properties are combined with enhanced biocompatibility, making it much more suitable for biomedical applications than synthetic nanomaterials. Moreover, PVX nanoparticles have very low toxicity in vivo, and superior pharmacokinetic profiles. This review focuses on the production of PVX nanoparticles engineered using chemical and/or biological techniques, and describes current and future opportunities and challenges for the application of PVX nanoparticles in medicine, diagnostics, materials science, and biocatalysis.

Protocol for Efficient Cell-Free Synthesis of Cowpea Chlorotic Mottle Virus-Like Particles Containing Heterologous RNAs

We report a protocol for efficient cell-free synthesis of cowpea chlorotic mottle virus (CCMV)-like particles containing a broad range of lengths and sequences of RNA. Our protocol starts with a purified stock of wild-type CCMV (protocols for harvesting and purifying the virus are detailed elsewhere) and features three basic steps: disassembly of the CCMV and purification of the capsid protein (CP) from the viral RNA; coassembly of the purified CP and an RNA of choice; and characterization of the assembly products. We highlight several key factors that increase the yield of the assembly reaction: the CP should be uncleaved and sufficiently free of viral RNA; the length of the RNA should be between about 100 and 4000 nucleotides; and the stoichiometry of CP and RNA should be 6-1 by mass. Additionally, we point out that separating the assembly reaction into multiple steps-by successively lowering the ionic strength and then the pH of the assembly buffers-results in the highest yields of well-formed, nuclease-resistant, CCMV-like particles. Finally, we describe methods for characterizing the assembly products using native agarose gel electrophoresis and negative-stain transmission electron microscopy.

Antibody Modification of p-Aminophenylalanine-Containing Proteins

The use of antibody conjugates for biomedical applications has garnered increased attention due to the ability of antibodies to specifically engage targets of interest. Despite these appealing qualities, the preparation of antibody-protein conjugates remains challenging. Here we detail an approach to attaching targeting antibodies to proteins of interest that combines advances in genetic code expansion and an efficient bioconjugation strategy. As an example, we prepare bacteriophage MS2 viral capsids bearing antibodies on their surfaces for applications in molecular targeting. This technique provides a modular framework to easily prepare antibody-MS2 conjugates in an efficient manner, even at low concentrations of the reacting biomolecules.

Encapsulation of Plant Viral Particles in Calcite Crystals

The concept of biomineralization and encapsulation of organic molecules into inorganic matrices to alter and enhance their physical properties has been evolved and perfected in natural systems. Being inspired by the natural biomineralization of foreign components into calcite, here the inclusion of a plant virus, cowpea mosaic virus (CPMV) of 5.4% by mass into crystals of calcite is reported. The viral particles are labeled with a fluorescent tag (Alexa Fluor 532), and are observed within the calcite matrix using confocal fluorescence microscopy. Upon encapsulation, the calcite crystals exhibit an irregular and aggregated morphology, as visualized with atomic force and electron microscopy. The viral particles protected inside the calcite crystals are able to resist harsh chemical agents. While spherical viral particles such as CPMV can be easily included in calcite, viruses such as the tobacco mosaic virus are not compatible with the host, presumably due to their high aspect ratio. The results provide a simple and scalable method to incorporate viral particles into inorganic matrix, and could prove useful in thermal stabilization of sensitive viral biological agents such as vaccines in the future.

Plant virus nanoparticles: Novel and robust nanocarriers for drug delivery and imaging

Nanoparticles have been gained much attention for biomedical applications. A promising type of nanocarriers is viral nanoparticles (VNPs) which are natural bio-nanomaterials derived from different type of viruses. Amongst VNPs, plant VNPs present several pros over general nanoparticles such as liposomes, dendrimers or quantum dots. Some of these advantages include: degradability, safety for human, known structures to atomic level, possibility of attaching ligand with vigorous control on structure, availability for genetic and chemical manipulations and very flexible methods to prepare them. Variety of plant viruses have been modified by chemical and genetic modification of their inner cavities and their outer-surfaces. These modifications provide suitable sites for attachment of markers and drug molecules for vascular imaging and tumor targeting. In this review a brief description of plant virus nanoparticles and their biomedical applications especially in drug delivery is provided. The methods of loading cargos in these VNPs and their final biofate are also reviewed.

Icosahedral plant viral nanoparticles - bioinspired synthesis of nanomaterials/nanostructures

Viral nanotechnology utilizes virus nanoparticles (VNPs) and virus-like nanoparticles (VLPs) of plant viruses as highly versatile platforms for materials synthesis and molecular entrapment that can be used in the nanotechnological fields, such as in next-generation nanoelectronics, nanocatalysis, biosensing and optics, and biomedical applications, such as for targeting, therapeutic delivery, and non-invasive in vivo imaging with high specificity and selectivity. In particular, plant virus capsids provide biotemplates for the production of novel nanostructured materials with organic/inorganic moieties incorporated in a very precise and controlled manner. Interestingly, capsid proteins of spherical plant viruses can self-assemble into well-organized icosahedral three-dimensional (3D) nanoscale multivalent architectures with high monodispersity and structural symmetry. Using viral genetic and protein engineering of icosahedral viruses with a variety of sizes, the interior, exterior and the interfaces between coat protein (CP) subunits can be manipulated to fabricate materials with a wide range of desirable properties allowing for biomineralization, encapsulation, infusion, controlled self-assembly, and multivalent ligand display of nanoparticles or molecules for varied applications. In this review, we discuss the various functional nanomaterials/nanostructures developed using the VNPs and VLPs of different icosahedral plant viruses and their nano(bio)technological and nanomedical applications.

Synthetic plant virology for nanobiotechnology and nanomedicine

Nanotechnology is a rapidly expanding field seeking to utilize nano-scale structures for a wide range of applications. Biologically derived nanostructures, such as viruses and virus-like particles (VLPs), provide excellent platforms for functionalization due to their physical and chemical properties. Plant viruses, and VLPs derived from them, have been used extensively in biotechnology. They have been characterized in detail over several decades and have desirable properties including high yields, robustness, and ease of purification. Through modifications to viral surfaces, either interior or exterior, plant-virus-derived nanoparticles have been shown to support a range of functions of potential interest to medicine and nano-technology. In this review we highlight recent and influential achievements in the use of plant virus particles as vehicles for diverse functions: from delivery of anticancer compounds, to targeted bioimaging, vaccine production to nanowire formation. WIREs Nanomed Nanobiotechnol 2017, 9:e1447. doi: 10.1002/wnan.1447 For further resources related to this article, please visit the WIREs website.

Bioengineered protein-based nanocage for drug delivery

Nature, in its wonders, presents and assembles the most intricate and delicate protein structures and this remarkable phenomenon occurs in all kingdom and phyla of life. Of these proteins, cage-like multimeric proteins provide spatial control to biological processes and also compartmentalizes compounds that may be toxic or unstable and avoids their contact with the environment. Protein-based nanocages are of particular interest because of their potential applicability as drug delivery carriers and their perfect and complex symmetry and ideal physical properties, which have stimulated researchers to engineer, modify or mimic these qualities. This article reviews various existing types of protein-based nanocages that are used for therapeutic purposes, and outlines their drug-loading mechanisms and bioengineering strategies via genetic and chemical functionalization. Through a critical evaluation of recent advances in protein nanocage-based drug delivery in vitro and in vivo, an outlook for de novo and in silico nanocage design, and also protein-based nanocage preclinical and future clinical applications will be presented.

Biomedical and Catalytic Opportunities of Virus-Like Particles in Nanotechnology

Within biology, molecules are arranged in hierarchical structures that coordinate and control the many processes that allow for complex organisms to exist. Proteins and other functional macromolecules are often studied outside their natural nanostructural context because it remains difficult to create controlled arrangements of proteins at this size scale. Viruses are elegantly simple nanosystems that exist at the interface of living organisms and nonliving biological machines. Studied and viewed primarily as pathogens to be combatted, viruses have emerged as models of structural efficiency at the nanoscale and have spurred the development of biomimetic nanoparticle systems. Virus-like particles (VLPs) are noninfectious protein cages derived from viruses or other cage-forming systems. VLPs provide incredibly regular scaffolds for building at the nanoscale. Composed of self-assembling protein subunits, VLPs provide both a model for studying materials' assembly at the nanoscale and useful building blocks for materials design. The robustness and degree of understanding of many VLP structures allow for the ready use of these systems as versatile nanoparticle platforms for the conjugation of active molecules or as scaffolds for the structural organization of chemical processes. Lastly the prevalence of viruses in all domains of life has led to unique activities of VLPs in biological systems most notably the immune system. Here we discuss recent efforts to apply VLPs in a wide variety of applications with the aim of highlighting how the common structural elements of VLPs have led to their emergence as paradigms for the understanding and design of biological nanomaterials.

Free-Standing, Nanopatterned Janus Membranes of Conducting Polymer-Virus Nanoparticle Arrays

Nanostructured mesoscale materials find wide-ranging applications in medicine and energy. Top-down manufacturing schemes are limited by the smallest dimension accessible; therefore, we set out to study a bottom-up approach mimicking biological systems, which self-assemble into systems that orchestrate complex energy conversion functionalities. Inspired by nature, we turned toward protein-based nanoparticle structures formed by plant viruses, specifically the cowpea mosaic virus (CPMV). We report the formation of hierarchical CPMV nanoparticle assemblies on colloidal-patterned, conducting polymer arrays using a protocol combining colloidal lithography, electrochemical polymerization, and electrostatic adsorption. In this approach, a hexagonally close-packed array of polystyrene microspheres was assembled on a conductive electrode to function as the sacrificial colloidal template. A thin layer of conducting polypyrrole material was electrodeposited within the interstices of the colloidal microspheres and monitored in situ using electrochemical quartz crystal microbalance with dissipation (EC-QCM-D). Etching the template revealed an inverse opaline conducting polymer pattern capable of forming strong electrostatic interactions with CPMV and therefore enabling immobilization of CPMV on the surface. The CPMV-polymer films were characterized by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Furthermore, molecular probe diffusion experiments revealed selective ion transport properties as a function of the presence of the CPMV nanoparticles on the surface. Lastly, by utilizing its electromechanical behavior, the polymer/protein membrane was electrochemically released as a free-standing film, which can potentially be used for developing high surface area cargo delivery systems, stimuli-responsive plasmonic devices, and chemical and biological sensors.

Coupling Peptide Antigens to Virus-Like Particles or to Protein Carriers Influences the Th1/Th2 Polarity of the Resulting Immune Response

We have conjugated the S9 peptide, a mimic of the group B streptococcal type III capsular polysaccharide, to different carriers in an effort to elicit an optimal immune response. As carriers, we utilized the soluble protein keyhole limpet hemocyanin and virus-like particles (VLPs) from two plant viruses, Cowpea Chlorotic Mottle Virus and Cowpea Mosaic Virus. We have found that coupling the peptide to the soluble protein elicits a Th2 immune response, as evidenced by the production of the peptide-specific IgG1 antibody and IL-4/IL-10 production in response to antigen stimulation, whereas the peptide conjugated to VLPs elicited a Th1 response (IgG2a, IFN-γ). Because the VLPs used as carriers package RNA during the assembly process, we hypothesize that this effect may result from the presence of nucleic acid in the immunogen, which affects the Th1/Th2 polarity of the response.

Utilizing Viral Nanoparticle/Dendron Hybrid Conjugates in Photodynamic Therapy for Dual Delivery to Macrophages and Cancer Cells

Photodynamic therapy (PDT) is a promising avenue for greater treatment efficacy of highly resistant and aggressive melanoma. Through photosensitizer attachment to nanoparticles, specificity of delivery can be conferred to further reduce potential side effects. While the main focus of PDT is the destruction of cancer cells, additional targeting of tumor-associated macrophages also present in the tumor microenvironment could further enhance treatment by eliminating their role in processes such as invasion, metastasis, and immunosuppression. In this study, we investigated PDT of macrophages and tumor cells through delivery using the natural noninfectious nanoparticle cowpea mosaic virus (CPMV), which has been shown to have specificity for the immunosuppressive subpopulation of macrophages and also targets cancer cells. We further explored conjugation of CPMV/dendron hybrids in order to improve the drug loading capacity of the nanocarrier. Overall, we demonstrated effective elimination of both macrophage and tumor cells at low micromolar concentrations of the photosensitizer when delivered with the CPMV bioconjugate, thereby potentially improving melanoma treatment.

Different applications of virus-like particles in biology and medicine: Vaccination and delivery systems

Virus-like particles (VLPs) mimic the whole construct of virus particles devoid of viral genome as used in subunit vaccine design. VLPs can elicit efficient protective immunity as direct immunogens compared to soluble antigens co-administered with adjuvants in several booster injections. Up to now, several prokaryotic and eukaryotic systems such as insect, yeast, plant, and E. coli were used to express recombinant proteins, especially for VLP production. Recent studies are also generating VLPs in plants using different transient expression vectors for edible vaccines. VLPs and viral particles have been applied for different functions such as gene therapy, vaccination, nanotechnology, and diagnostics. Herein, we describe VLP production in different systems as well as its applications in biology and medicine.

Protein cages and synthetic polymers: a fruitful symbiosis for drug delivery applications, bionanotechnology and materials science

Protein cages have become essential tools in bionanotechnology due to their well-defined, monodisperse, capsule-like structure. Combining them with synthetic polymers greatly expands their application, giving rise to novel nanomaterials fore.g.drug-delivery, sensing, electronic devices and for uses as nanoreactors.

Tropism of CPMV to Professional Antigen Presenting Cells Enables a Platform to Eliminate Chronic Infections

Chronic viral infections (e.g., HIV, HBV, HCV) represent a significant source of morbidity and mortality with over 500 million people infected worldwide. Dendritic cells (DCs) and macrophages are key cell types for productive viral replication and persistent systemic infection. We demonstrate that the plant virus cowpea mosaic virus (CPMV) displays tropism for such antigen presenting cells in both mice and humans, thus making it an ideal candidate for targeted drug delivery toward viral infections. Furthermore, we show inhibition of a key host protein for viral infection, site-1 protease (S1P), using the small molecule PF-429242 in the model pathogen arenavirus lymphocytic choriomeningitis virus (LCMV) limits viral growth. By packaging PF-429242 in CPMV, we are able to control drug release and efficiently deliver the drug. This sets the groundwork for utilizing the natural tropism of CPMV for a therapeutic approach that specifically targets cell types most commonly subverted by chronic viruses.

Virus Nanoparticles Mediated Osteogenic Differentiation of Bone Derived Mesenchymal Stem Cells

There are few methodologies that allow manipulating a biomaterial surface at nanometer scale, which controllably influence different cellular functions. In this study, virus nanoparticles with different structural features are selected to prepare 2D substrates with defined nanoscale topographies and the cellular responses are investigated. It is demonstrated that the viral nanoparticle based substrates could accelerate and enhance osteogenesis of bone derived mesenchymal stem cells as indicated by the upregulation of osteogenic markers, including bone morphogenetic protein-2, osteocalcin, and osteopontin, at both gene and protein expression levels. Moreover, alkaline phosphatase activity and calcium mineralization, both indicators for a -successful bone formation, are also increased in cells grown on these nanoscale possessed substrates. These discoveries and developments present a new paradigm for nanoscale engineering of a biomaterial surface.

Synthetically Modified Viral Capsids as Versatile Carriers for Use in Antibody-Based Cell Targeting

The present study describes an efficient and reliable method for the preparation of MS2 viral capsids that are synthetically modified with antibodies using a rapid oxidative coupling strategy. The overall protocol delivers conjugates in high yields and recoveries, requires a minimal excess of antibody to achieve modification of more than 95% of capsids, and can be completed in a short period of time. Antibody-capsid conjugates targeting extracellular receptors on human breast cancer cell lines were prepared and characterized. Notably, conjugation to the capsid did not significantly perturb the binding of the antibodies, as indicated by binding affinities similar to those obtained for the parent antibodies. An array of conjugates was synthesized with various reporters on the interior surface of the capsids to be used in cell studies, including fluorescence-based flow cytometry, confocal microscopy, and mass cytometry. The results of these studies lay the foundation for further exploration of these constructs in the context of clinically relevant applications, including drug delivery and in vivo diagnostics.

Boosting Humoral Immune Responses to Tumor-associated Carbohydrate Antigens with Virus-like Particles

The development of carbohydrate-based anticancer vaccines is an attractive approach towards the prevention and treatment of cancer. The weak immunogenicity of carbohydrate antigens and tolerance by the immune system are major obstacles towards the design of effective cancer vaccines. Recently, virus-like particles have been shown to be a promising platform to overcome the aforementioned difficulties. In this chapter, we provide an overview on the structural and immunological features of virus-like particles in eliciting anti-carbohydrate antibody responses. The immuno-potentiating activities of several virus-like particle systems are compared, and insights into critical factors of virus-like particles that help shape the anti-carbohydrate responses are discussed.

Interface of physics and biology: engineering virus-based nanoparticles for biophotonics

Virus-based nanoparticles (VNPs) have been used for a wide range of applications, spanning basic materials science and translational medicine. Their propensity to self-assemble into precise structures that offer a three-dimensional scaffold for functionalization has led to their use as optical contrast agents and related biophotonics applications. A number of fluorescently labeled platforms have been developed and their utility in optical imaging demonstrated, yet their optical properties have not been investigated in detail. In this study, two VNPs of varying architectures were compared side-by-side to determine the impact of dye density, dye localization, conjugation chemistry, and microenvironment on the optical properties of the probes. Dyes were attached to icosahedral cowpea mosaic virus (CPMV) and rod-shaped tobacco mosaic virus (TMV) through a range of chemistries to target particular side chains displayed at specific locations around the virus. The fluorescence intensity and lifetime of the particles were determined, first using photochemical experiments on the benchtop, and second in imaging experiments using tissue culture experiments. The virus-based optical probes were found to be extraordinarily robust under ultrashort, pulsed laser light conditions with a significant amount of excitation energy, maintaining structural and chemical stability. The most effective fluorescence output was achieved through dye placement at optimized densities coupled to the exterior surface avoiding conjugated ring systems. Lifetime measurements indicate that fluorescence output depends not only on spacing the fluorophores, but also on dimer stacking and configurational changes leading to radiationless relaxation—and these processes are related to the conjugation chemistry and nanoparticle shape. For biological applications, the particles were also examined in tissue culture, from which it was found that the optical properties differed from those found on the benchtop due to effects from cellular processes and uptake kinetics. Data indicate that fluorescent cargos are released in the endolysosomal compartment of the cell targeted by the virus-based optical probes. These studies provide insight into the optical properties and fates of fluorescent proteinaceous imaging probes. The cellular release of cargo has implications not only for virus-based optical probes, but also for drug delivery and release systems.

CPMV-induced synthesis of hollow mesoporous SiO2 nanocapsules with excellent performance in drug delivery

Synthesis of CPMV- hollow silica nanocapsules and their use in nanomedicine.

Overexpression and self-assembly of virus-like particles in Nicotiana benthamiana by a single-vector DNA replicon system

Based on recent developments, virus-like particles (VLPs) are considered to be perfect candidates as nanoplatforms for applications in materials science and medicine. To succeed, mass production of VLPs and self-assembly into a correct form in plant systems are key factors. Here, we report expression of synthesized coat proteins of the three viruses, Brome mosaic virus, Cucumber mosaic virus, and Maize rayado fino virus, in Nicotiana benthamiana and production of self-assembled VLPs by transient expression system using agroinfiltration. Each coat protein was synthesized and cloned into a pBYR2fp single replicon vector. Target protein expression in cells containing p19 was fourfold higher than that of cells lacking p19. After agroinfiltration, protein expression was analyzed by SDS-PAGE and quantitative image analyzer. Quantitative analysis showed that BMVCP, CMVCP, and MRFVCP concentrations were 0.5, 1.0, and 0.8 mg · g(-1) leaf fresh weight, respectively. VLPs were purified by sucrose cushion ultracentrifugation and then analyzed by transmission electron microscopy. Our results suggested that BMVCP and CMVCP proteins expressed in N. benthamiana leaves were able to correctly self-assemble into particles. Moreover, we evaluated internal cavity accessibility of VLPs to load foreign molecules. Finally, plant growth conditions after agroinfiltration are critical for increasing heterologous protein expression levels in a transient expression system.

Virus-templated plasmonic nanoclusters with icosahedral symmetry via directed self-assembly

The assembly of plasmonic nanoparticles with precise spatial and orientational order may lead to structures with new electromagnetic properties at optical frequencies. The directed self-assembly method presented controls the interparticle-spacing and symmetry of the resulting nanometer-sized elements in solution. The self-assembly of three-dimensional (3D), icosahedral plasmonic nanosclusters (NCs) with resonances at visible wavelengths is demonstrated experimentally. The ideal NCs consist of twelve gold (Au) nanospheres (NSs) attached to thiol groups at predefined locations on the surface of a genetically engineered cowpea mosaic virus with icosahedral symmetry. In situ dynamic light scattering (DLS) measurements confirm the NSs assembly on the virus. Transmission electron micrographs (TEM) demonstrate the ability of the self-assembly method to control the nanoscopic symmetry of the bound NSs, which reflects the icosahedral symmetry of the virus. Both, TEM and DLS show that the NCs comprise of a distribution of capsids mostly covered (i.e., 6-12 NS/capsid) with NSs. 3D finite-element simulations of aqueous suspensions of NCs reproduce the experimental bulk absorbance measurements and major features of the spectra. Simulations results show that the fully assembled NCs give rise to a 10-fold surface-averaged enhancement of the local electromagnetic field.