Separation of pure and immunoreactive virus-like particles using gel filtration chromatography following immobilized metal ion affinity chromatography

Application of immobilized metal affinity chromatography in proteomics

It has been proved that the progress of proteomics is mostly determined by the development of advanced and sensitive protein separation technologies. Immobilized metal affinity chromatography (IMAC) is a powerful protein fractionation method used to enrich metal-associated proteins and peptides. In proteomics, IMAC has been widely employed as a prefractionation method to increase the resolution in protein separation. The combination of IMAC with other protein analytical technologies has been successfully utilized to characterize metalloproteome and post-translational modifications. In the near future, newly developed IMAC integrated with other proteomic methods will greatly contribute to the revolution of expression, cell-mapping and structural proteomics.

A potential nanobiotechnology platform based on infectious bursal disease subviral particles

We describe a novel nanobiotechnology platform based on subviral particles derived from infectious bursal disease virus (IBD-SVPs). The major virus coat protein VP2 assembles into spherical, 23 nm SVPs when expressed as a heterologous protein in the yeast Pichia pastoris. We recovered up to 38 mg of IBD-SVPs at > 95% purity from 1 L of recombinant yeast culture. The purified particles were able to tolerate organic solvents up to 20% concentration (ethanol or dimethylsulfoxide), they resisted temperatures up to 65 °C and remained stable over a wide pH range (2.5-9.0). We achieved bioconjugation to the amine groups of lysine residues and to the carboxyl groups of aspartic and glutamic acid residues, allowing the functionalization of IBD-SVPs with biotin. The accessibility of surface amine groups was measured using Alexa Fluor 488 N-hydroxysuccinimide (NHS) ester, an amine-selective fluorescent dye, revealing that approximately 60 dye molecules were attached to the surface of each particle. IBD-SVPs can therefore be exploited as a robust and versatile nanoscaffold to display diverse functional ligands.

Chicken heat shock protein 90 is a component of the putative cellular receptor complex of infectious bursal disease virus

Infectious bursal disease virus (IBDV) causes a highly contagious disease in young chicks and leads to significant economic losses in the poultry industry. The capsid protein VP2 of IBDV plays an important role in virus binding and cell recognition. VP2 forms a subviral particle (SVP) with immunogenicity similar to that of the IBDV capsid. In the present study, we first showed that SVP could inhibit IBDV infection to an IBDV-susceptible cell line, DF-1 cells, in a dose-dependent manner. Second, the localizations of the SVP on the surface of DF-1 cells were confirmed by fluorescence microscopy, and the specific binding of the SVP to DF-1 cells occurred in a dose-dependent manner. Furthermore, the attachment of SVP to DF-1 cells was inhibited by an SVP-induced neutralizing monoclonal antibody against IBDV but not by denatured-VP2-induced polyclonal antibodies. Third, the cellular factors in DF-1 cells involved in the attachment of SVP were purified by affinity chromatography using SVP bound on the immobilized Ni(2+) ions. A dominant factor was identified as being chicken heat shock protein 90 (Hsp90) (cHsp90) by mass spectrometry. Results of biotinylation experiments and indirect fluorescence assays indicated that cHsp90 is located on the surface of DF-1 cells. Virus overlay protein binding assays and far-Western assays also concluded that cHsp90 interacts with IBDV and SVP, respectively. Finally, both Hsp90 and anti-Hsp90 can inhibit the infection of DF-1 cells by IBDV. Taken together, for the first time, our results suggest that cHsp90 is part of the putative cellular receptor complex essential for IBDV entry into DF-1 cells.

Downstream processing of triple layered rotavirus like particles

Rotavirus like particles (RLPs) constitute a potential vaccine for the prevention of rotavirus disease, responsible for the death of more than half a million children each year. Increasing demands for pre-clinical trials material require the development of reproducible, scaleable and cost-effective purification strategies as alternatives to the traditional laboratory scale CsCl density gradient ultracentrifugation methods commonly used for the purification of these complex particles. Self-assembled virus like particles (VLPs) composed by VP2, VP6 and VP7 rotavirus proteins (VLPs 2/6/7) were produced in 5l scale using the insect cells/baculovirus expression system. A purification process using depth filtration, ultrafiltration and size exclusion chromatography as stepwise unit operations was developed. Removal of non-assembled rotavirus proteins, concurrently formed particles (RLP 2/6), particle aggregates and products of particle degradation due to shear was achieved. Particle stability during storage was studied and assessed using size exclusion chromatography as an analytical tool. Formulations containing either glycerol (10% v/v) or trehalose (0.5 M) were able to maintain 75% of intact triple layered VLPs, at 4 degrees C, up to 4 months. The overall recovery yield was 37% with removal of 95% of host cell proteins and 99% of the host cell DNA, constituting a promising strategy for the downstream processing of other VLPs.

Purification of VP3 protein of infectious bursal disease virus using nickel ion-immobilized regenerated cellulose-based membranes

In this study, hexa-histidine tagged VP3 protein of infectious bursal disease virus (IBDV) was purified using immobilized metal ion affinity technique from the fermentation of Escherichia coli BL21 (DE3) containing a recombinant plasmid with a VP3 gene. The purification efficiencies of VP3 protein (TVP3 and DeltaTVP3) using Ni(2+)-NTA commercial agarose gels and Ni(2+)-IDA regenerated cellulose-based membranes at 4 degrees C were compared. A good washing condition for removing most impurity proteins was found as 20 mM NaH(2)PO(4), 500 mM NaCl, 40 mM imidazole, pH 7.8, whereas an efficient elution condition was 20 mM NaH(2)PO(4), 500 mM NaCl, 500 or 750 mM imidazole, pH 7.8. By applying these conditions to the flow experiments, similar recovery (86-88%) and purity (98-99%) for VP3 were obtained in both gel column (1 ml gel) and membrane cartridge (four membrane disks) under the flow rate of 1.7 ml/min for protein loading and 2.7 ml/min for protein elution. Regarding that the membrane process exhibited some advantages such as shorter residence time and lower cost, a better process efficiency in a large-scale system could be expected for the Ni(2+)-IDA membranes.

Purification of capsid-like particles of infectious bursal disease virus (IBDV) VP2 expressed in E. coli with a metal-ion affinity membrane system

Protein VP2, matured from the polyprotein encoded by the genome of infectious bursal disease virus (IBDV) and the primary host-protective immunogen of this virus, together with its two N-terminal truncated mutants were cloned and expressed in Escherichia coli. To obtain pure recombinant proteins for the development of an efficient subunit vaccine against IBDV infection, these three proteins were fused with six additional histidine residues at their C-termini as a His-purification-tag. Following purification employing immobilized metal-ion (Ni2+) affinity chromatography (IMAC), a purification fold of approximately 104 was achieved. Electron microscopic observation also demonstrated that all three E. coli-derived proteins form the morphology of icosahedral particles of approximately 25 nm in diameter. To reduce the cost of resin used for IMAC, self-prepared immobilized metal-ion affinity membranes (IMAM), i.e., commercial, regenerated cellulose membrane modified with iminodiacetic acid and immobilized with nickel ions, was applied to purify particles formed by these three proteins. A 104-fold of purification efficiency was also achieved by this membrane, showing that under the same conditions the recovery and purification efficiency of IMAM are comparable with those of IMAC. The pure VP2-formed particles thus obtained, coupled with their uniform dimensions, not only facilitate a better understanding of the structural biology of these immunogenic particles but also help the development of improved vaccines against this avian virus.

Characterization of particles formed by the precursor protein VPX of infectious bursal disease virus in insect Hi-5 cells: implication on its proteolytic processing

The precursor (VPX) of host immunogen VP2 protein for infectious bursal disease virus (IBDV) was expressed in insect Sf9 and Hi-5 cells, and the types of particles generated as well as the immunogenicity induced by these particles were examined. Recombinant VPXH (rVPXH) protein, expressed in Hi-5 cells at an expression level 4x higher than in Sf9 cells, was efficiently processed by proteases to yield VP2-like proteins with corresponding molecular weight, a phenomenon not observed previously. At least three structures of particles were observed for VPXH and VP2-like proteins purified by immobilized metal-ion affinity chromatography (MAC). In addition to the two previously identified twisted tubular and isometric particle structures, there was a new one: icosahedral particles of approximately 25 nm in diameter. The purified particles were further separated by gel-filtration chromatography (GFC) linking with HPLC, which was able to resolve the isometric from icosahedral particles better than ultracentrifugation. Chromatographic results indicate that rVPXH protein mainly involved in the formation of the isometric particle structure and occasionally twisted tubular structure, and the icosahedral particles were formed by the degraded products of rVPXH (VP2-like proteins). Thus, by combining IMAC and GFC, it was shown that VPX was processed efficiently to yield VP2-like protein that could form small virus-like particles in Hi-5 cells. Finally, we demonstrated that virus-neutralizing antibodies were induced when susceptible chickens were vaccinated with the IMAC-purified rVPXH protein (40 microg per bird). This indicates that these particles are highly immunogenic and might serve as an alternative vaccine candidate for the development of IBDV subunit vaccine.