Disulfide linkage and structure of highly stable yeast-derived virus-like particles of murine polyomavirus

Genetically Engineered, Multichromophore Virus-Like Nanoparticles with Ultranarrow Distribution of Emission Intensity

Variance in the properties of optical mesoscopic probes is often a limiting factor in applications. In the thermodynamic limit, the smaller the probe, the larger the relative variance. However, specific viral protein cages can assemble efficiently outside the bounds of statistical fluctuations at equilibrium through a process that is characterized by intrinsic quality-control and self-limiting capabilities. In this paper, an approach is described that leverages stoichiometric and structural accuracy in the murine polyoma virus capsid assembly to demonstrate bright, narrowly distributed fluorescence intensity from multichromophore particles that surpass state-of-the-art fluorescent nanosphere probes. Charge-detection mass spectrometry analysis demonstrated that proteins resulting from the fusion of superfolding green fluorescent protein (sfGFP) murine polyoma virus coat proteins self-assemble in vitro into virus-like particles that have similar stoichiometry as virus-like particles formed from wild-type virus coat proteins. Single-particle analysis by total internal reflection fluorescence microscopy provided evidence for a narrow fluorescence intensity that reflects stoichiometric accuracy of the construct.

Effect and mechanism of C-terminal cysteine on the properties of HEV p222 protein

Preliminary investigations have demonstrated that the cysteines located at the C-terminus of HEV ORF2 protein exhibits disulfide bonding capability during virus-like particles (VLPs) assembly. However, the effect and mechanism underlying the pairing of disulfide bonds formed by C627, C630, and C638 remains unclear. The p222 protein encompasses C-terminus and serves as a representative of HEV ORF2 to investigate the specific impacts of C627, C630, and C638. The three cysteines were subjected to site-directed mutagenesis and expressed in prokaryotes; Both the mutated proteins and p222 underwent polymerization except for p222A; Surprisingly, only p222 was observed as abundant spherical particles under transmission electron microscope (TEM); Stability and immunogenicity of the p222 exhibited higher than other mutated proteins; LC/MS/MS analysis identified four disulfide bonds in the p222. The novel findings suggest that the three cysteines contribute to structural and functional properties of ORF2 protein, highlighting the indispensability of each cysteine.

Yeast-Based Virus-like Particles as an Emerging Platform for Vaccine Development and Delivery

Virus-like particles (VLPs) are empty, nanoscale structures morphologically resembling viruses. Internal cavity, noninfectious, and particulate nature with a high density of repeating epitopes, make them an ideal platform for vaccine development and drug delivery. Commercial use of Gardasil-9 and Cervarix showed the usefulness of VLPs in vaccine formulation. Further, chimeric VLPs allow the raising of an immune response against different immunogens and thereby can help reduce the generation of medical or clinical waste. The economically viable production of VLPs significantly impacts their usage, application, and availability. To this end, several hosts have been used and tested. The present review will discuss VLPs produced using different yeasts as fermentation hosts. We also compile a list of studies highlighting the expression and purification of VLPs using a yeast-based platform. We also discuss the advantages of using yeast to generate VLPs over other available systems. Further, the issues or limitations of yeasts for producing VLPs are also summarized. The review also compiles a list of yeast-derived VLP-based vaccines that are presently in public use or in different phases of clinical trials.

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.

Human polyomaviruses and cancer: an overview

The name of the family Polyomaviridae, derives from the early observation that cells infected with murine polyomavirus induced multiple (poly) tumors (omas) in immunocompromised mice. Subsequent studies showed that many members of this family exhibit the capacity of mediating cell transformation and tumorigenesis in different experimental models. The transformation process mediated by these viruses is driven by viral pleiotropic regulatory proteins called T (tumor) antigens. Similar to other viral oncoproteins T antigens target cellular regulatory factors to favor cell proliferation, immune evasion and downregulation of apoptosis. The first two human polyomaviruses were isolated over 45 years ago. However, recent advances in the DNA sequencing technologies led to the rapid identification of additional twelve new polyomaviruses in different human samples. Many of these viruses establish chronic infections and have been associated with conditions in immunosuppressed individuals, particularly in organ transplant recipients. This has been associated to viral reactivation due to the immunosuppressant therapy applied to these patients. Four polyomaviruses namely, Merkel cell polyomavirus (MCPyV), Trichodysplasia spinulosa polyomavirus (TSPyV), John Cunningham Polyomavirus (JCPyV) and BK polyomavirus (BKPyV) have been associated with the development of specific malignant tumors. However, present evidence only supports the role of MCPyV as a carcinogen to humans. In the present review we present a summarized discussion on the current knowledge concerning the role of MCPyV, TSPyV, JCPyV and BKPyV in human cancers.

Inhibitor-GCPII Interaction: Selective and Robust System for Targeting Cancer Cells with Structurally Diverse Nanoparticles

Glutamate carboxypeptidase II (GCPII) is a membrane protease overexpressed by prostate cancer cells and detected in the neovasculature of most solid tumors. Targeting GCPII with inhibitor-bearing nanoparticles can enable recognition, imaging, and delivery of treatments to cancer cells. Compared to methods based on antibodies and other large biomolecules, inhibitor-mediated targeting benefits from the low molecular weight of the inhibitor molecules, which are typically stable, easy-to-handle, and able to bind the enzyme with very high affinity. Although GCPII is established as a molecular target, comparing previously reported results is difficult due to the different methodological approaches used. In this work, we investigate the robustness and limitations of GCPII targeting with a diverse range of inhibitor-bearing nanoparticles (various structures, sizes, bionanointerfaces, conjugation chemistry, and surface densities of attached inhibitors). Polymer-coated nanodiamonds, virus-like particles based on bacteriophage Qβ and mouse polyomavirus, and polymeric poly(HPMA) nanoparticles with inhibitors attached by different means were synthesized and characterized. We evaluated their ability to bind GCPII and interact with cancer cells using surface plasmon resonance, inhibition assay, flow cytometry, and confocal microscopy. Regardless of the diversity of the investigated nanosystems, they all strongly interact with GCPII (most with low picomolar K_i values) and effectively target GCPII-expressing cells. The robustness of this approach was limited only by the quality of the nanoparticle bionanointerface, which must be properly designed by adding a sufficient density of hydrophilic protective polymers. We conclude that the targeting of cancer cells overexpressing GCPII is a viable approach transferable to a broad diversity of nanosystems.

Adenovirus Dodecahedron, a VLP, Can be Purified by Size Exclusion Chromatography Instead of Time-Consuming Sucrose Density Gradient Centrifugation

Adenoviral dodecahedron (Dd) is a virus-like particle composed of twelve pentameric penton base (Pb) proteins, responsible for adenovirus cell penetration. It is generated spontaneously in the baculovirus system upon expression of the Pb gene of adenovirus serotype 3. This particle shows remarkable cell penetration ability with 2,00,000-3,00,000 Dd internalized into one cell in culture, conceivably delivering several millions of foreign cargo molecules to the target cell. We have used it in the past for delivery of small drugs as well as a vaccination platform, in which Dd serves as a particulate vaccine delivery system. Since development of new biomedicals depends strongly on the cost of their expression and purification, we attempted, albeit unsuccessfully, to obtain Dd expression in bacteria. We therefore retained its expression in the baculovirus/insect cells system but introduced significant improvements in the protocols for Dd expression and purification, leading to considerable savings in time and improved yield.

Design of a VLP-nanovehicle for CYP450 enzymatic activity delivery

BACKGROUND

The intracellular delivery of enzymes for therapeutic use has a promising future for the treatment of several diseases such as genetic disorders and cancer. Virus-like particles offer an interesting platform for enzymatic delivery to targeted cells because of their great cargo capacity and the enhancement of the biocatalyst stability towards several factors important in the practical application of these nanoparticles.

RESULTS

We have designed a nano-bioreactor based on the encapsulation of a cytochrome P450 (CYP) inside the capsid derived from the bacteriophage P22. An enhanced peroxigenase, CYPBM3, was selected as a model enzyme because of its potential in enzyme prodrug therapy. A total of 109 enzymes per capsid were encapsulated with a 70 % retention of activity for cytochromes with the correct incorporation of the heme cofactor. Upon encapsulation, the stability of the enzyme towards protease degradation and acidic pH was increased. Cytochrome P450 activity was delivered into Human cervix carcinoma cells via transfecting P22-CYP nanoparticles with lipofectamine.

CONCLUSION

This work provides a clear demonstration of the potential of biocatalytic virus-like particles as medical relevant enzymatic delivery vehicles for clinical applications.

Assembly and Purification of Polyomavirus-Like Particles from Plants

Polyomaviruses are small DNA viruses that have a history of use in biotechnology. The capsids of a number of species have been developed into experimental prophylactic and therapeutic virus-like particle (VLP) vaccines. In order to explore plants as a host for the expression and purification of polyomavirus-like particles, we have transiently expressed the major capsid protein, VP1, in Nicotiana benthamiana leaves. Deletion of a polybasic motif from the N-terminal region of VP1 resulted in increased expression as well as reduced necrosis of leaf tissue, which was associated with differences in subcellular localisation and reduced DNA binding by the deletion variant (ΔVP1). Self-assembled VLPs were recovered from tissue expressing both wild-type VP1 and ΔVP1 by density gradient ultracentrifugation. VLPs composed of ΔVP1 were more homogenous than wtVPLs and, unlike the latter, did not encapsidate nucleic acid. Such homogenous, empty VLPs are of great interest in biotechnology and nanotechnology. In addition, we show that both MPyV VLP variants assembled in plants can be produced with encapsidated foreign protein. Thus, this study demonstrates the utility of plant-based expression of polyomavirus-like particles and the suitability of this host for further developments in polyomavirus-based technologies.

Production of recombinant VP1-derived virus-like particles from novel human polyomaviruses in yeast

BACKGROUND

Eleven new human polyomaviruses (HPyVs) have been identified in the last decade. Serological studies show that these novel HPyVs sub-clinically infect humans at an early age. The routes of infection, entry pathways, and cell tropism of new HPyVs remain unknown. VP1 proteins of polyomaviruses can assembly into virus-like particles (VLPs). As cell culturing systems for HPyV are currently not available, VP1-derived VLPs may be useful tools in basic research and biotechnological applications.

RESULTS

Recombinant VP1-derived VLPs from 11 newly identified HPyVs were efficiently expressed in yeast. VP1 proteins derived from Merkel cell polyomavirus (MCPyV), trichodysplasia spinulosa-associated polyomavirus (TSPyV), and New Jersey polyomavirus (NJPyV) self-assembled into homogeneous similarly-sized VLPs. Karolinska Institutet polyomavirus (KIPyV), HPyV7, HPyV9, HPyV10, and St. Louis polyomavirus (STLPyV) VP1 proteins formed VLPs that varied in size with diameters ranging from 20 to 60 nm. Smaller-sized VLPs (25-35 nm in diameter) predominated in preparations from Washington University polyomavirus (WUPyV) and HPyV6. Attempts to express recombinant HPyV12 VP1-derived VLPs in yeast indicate that translation of VP1 might start at the second of two potential translation initiation sites in the VP1-encoding open reading frame (ORF). This translation resulted in a 364-amino acid-long VP1 protein, which efficiently self-assembled into typical PyV VLPs. MCPyV-, KIPyV-, TSPyV-, HPyV9-, HPyV10-, and HPyV12-derived VLPs showed hemagglutination (HA) assay activity in guinea pig erythrocytes, whereas WUPyV-, HPyV6-, HPyV7-, STLPyV- and NJPyV-derived VP1 VLPs did not.

CONCLUSIONS

The yeast expression system was successfully utilized for high-throughput production of recombinant VP1-derived VLPs from 11 newly identified HPyVs. HPyV12 VP1-derived VLPs were generated from the second of two potential translation initiation sites in the VP1-encoding ORF. Recombinant VLPs produced in yeast originated from different HPyVs demonstrated distinct HA activities and may be useful in virus diagnostics, capsid structure studies, or investigation of entry pathways and cell tropism of HPyVs until cell culture systems for new HPyVs are developed.

Genome Sequence of a Fish-Associated Polyomavirus, Black Sea Bass (Centropristis striata) Polyomavirus 1

All known polyomaviruses are associated with mammals or birds. Using virion enrichment, random-primed rolling circle amplification, and deep sequencing, we identified a polyomavirus associated with black sea bass (Centropristis striata). The virus has a variety of novel genetic features, suggesting a long evolutionary separation from polyomaviruses of terrestrial animals.