Strategies for the purification and characterization of protein scaffolds for the production of hybrid nanobiomaterials

Spectroscopic analysis of the bacterially expressed head domain of rotavirus VP6

The rotavirus capsid protein VP6 forms the middle of three protein layers and is responsible for many critical steps in the viral life cycle. VP6 as a structural protein can be used in various applications including as a subunit vaccine component. The head domain of VP6 (VP6H) contains key sequences that allow the protein to trimerize and that represent epitopes that are recognized by human antibodies in the viral particle. The domain is rich in β-sheet secondary structures. Here, VP6H was solubilised from bacterial inclusion bodies and purified using a single affinity chromatography step. Spectral (far-UV circular dichroism and intrinsic tryptophan fluorescence) analysis revealed that the purified domain had native-like secondary and tertiary structures. The domain could maintain structure up to 44°C during thermal denaturation following which structural changes result in an intermediate forming and finally irreversible aggregation and denaturation. The chemical denaturation with urea and guanidinium hydrochloride produces intermediates that represent a loss in the cooperativity. The VP6H domain is stable and can fold to produce its native structure in the absence of the VP6 base domain but cannot be defined as an independent folding unit.

Rotavirus Particle Disassembly and Assembly In Vivo and In Vitro

Rotaviruses (RVs) are non-enveloped multilayered dsRNA viruses that are major etiologic agents of diarrheal disease in humans and in the young in a large number of animal species. The viral particle is composed of three different protein layers that enclose the segmented dsRNA genome and the transcriptional complexes. Each layer defines a unique subparticle that is associated with a different phase of the replication cycle. Thus, while single- and double-layered particles are associated with the intracellular processes of selective packaging, genome replication, and transcription, the viral machinery necessary for entry is located in the third layer. This modular nature of its particle allows rotaviruses to control its replication cycle by the disassembly and assembly of its structural proteins. In this review, we examine the significant advances in structural, molecular, and cellular RV biology that have contributed during the last few years to illuminating the intricate details of the RV particle disassembly and assembly processes.

Expression and Purification of Porcine Rotavirus Structural Proteins in Silkworm Larvae as a Vaccine Candidate

In this study, silkworm larvae were used for expression of porcine rotavirus A (KS14 strain) inner capsid protein, VP6, and outer capsid protein, VP7. Initially, VP6 was fused with Strep-tag II and FLAG-tag (T-VP6), and T-VP6 was fused further with the signal peptide of Bombyx mori 30k6G protein (30k-T-VP6). T-VP6 and 30 k-T-VP6 were then expressed in the fat body and hemolymph of silkworm larvae, respectively, with respective amounts of 330 μg and 50 μg per larva of purified protein. Unlike T-VP6, 30k-T-VP6 was N-glycosylated due to attached signal peptide. Also, VP7 was fused with PA-tag (VP7-PA). Additionally, VP7 was fused with Strep-tag II, FLAG-tag, and the signal peptide of Bombyx mori 30k6G protein (30k-T-ΔVP7). Both VP7-PA and 30k-T-ΔVP7 were expressed in the hemolymph of silkworm larvae, with respective amounts of 26 μg and 49 μg per larva of purified protein, respectively. The results from our study demonstrated that T-VP6 formed nanoparticles of greater diameter compared with the ones formed by 30k-T-VP6. Also, higher amount of VP6 expressed in silkworm larvae reveal that VP6 holds the potential for its use in vaccine development against porcine rotavirus with silkworm larvae as a promising host for the production of such multi-subunit vaccines.

Chronological Age Estimation of Male Occipital Bone Based on FTIR and Raman Microspectroscopy

Age-related changes in bone tissue have always been an important part of bone research, and age estimation is also of great significance in forensic work. In our study, FTIR and Raman microspectroscopy were combined to explore the structural and chronological age-related changes in the occipital bones of 40 male donors. The FTIR micro-ATR mode not only achieves the comparison of FTIR and Raman efficiency but also provides a new pattern for the joint detection of FTIR and Raman in hard tissue. Statistical analysis and PCA results revealed that the structure had little effect on the FTIR and Raman results. The FTIR and Raman mineral/matrix ratio, carbonate/phosphate ratio, crystallinity, and collagen maturity of the whole showed an increasing trend during maturation, and a significant correlation was found between FTIR and Raman by comparing four outcomes. Furthermore, the results indicated that the cutoff point of the change in the relative proportion of organic matrix and inorganic minerals in males was between 19 and 35 years old, and the changes in the relative proportion of organic matrix and inorganic minerals may play a key role in age estimation. Ultimately, we established age estimation regression models. The FTIR GA-PLS regression model has the best performance and is more suitable for our experiment (RMSECV = 10.405, RMSEP = 9.2654, R²CV = 0.814, and R²Pred = 0.828). Overall, FTIR and Raman combined with chemometrics are an ideal method to estimate chronological age based on age-dependent component changes in male occipital bones. Our experiment provides a proof of concept and potential experimental method for chronological age estimation.

Rotavirus VP6: involvement in immunogenicity, adjuvant activity, and use as a vector for heterologous peptides, drug delivery, and production of nano-biomaterials

The first-generation, live attenuated rotavirus (RV) vaccines, such as RotaTeq and Rotarix, were successful in reducing the number of RV-induced acute gastroenteritis (AGE) and child deaths globally. However, the low efficacy of these first-generation oral vaccines, coupled with safety concerns, required development of improved RV vaccines. The highly conserved structural protein VP6 is highly immunogenic, and it can generate self-assembled nano-sized structures, including tubes and spheres (virus-like particles; VLPs). Amongst the RV proteins, only VP6 shows these features. Interestingly, VP6-assembled structures, in addition to being highly immunogenic, have several other useful characteristics that could allow them to be used as adjuvants, immunological carriers, and drug-delivery vehicles as well as acting a scaffold for production of valuable nano-biomaterials. This review provides an overview of the self-assembled nano-sized structures of VP6-tubes/VLPs and their various functions.

A novel method for the in vitro assembly of virus-like particles and multimeric proteins

OBJECTIVE

To develop a method for the efficient assembly of viral or multimeric proteins into virus-like particles (VLP) or other macro structures.

RESULTS

Protein monomers were assembled by eliminating calcium ions through precipitation. The model protein, rotavirus VP6, assembled into stable, long nanotubes with better quality than the assemblies obtained directly from cell culture. Nanotube length was directly proportional to the initial concentration of VP6 monomers, in accordance with the classic nucleation theory of capsid assembly. The quality of the obtained assemblies was confirmed when the nanotubes were functionalized with metals, yielding unique nanobiomaterials. Assembly efficiency was improved in comparison with other previously proposed methods.

CONCLUSIONS

The novel method presented here is simpler and faster than other reported methods for the assembly and disassembly of viral proteins, a step needed for most applications.

Gold Nanoclusters, Gold Nanoparticles, and Analytical Techniques for Their Characterization

Many reliable and reproducible methods exist for manufacturing gold nanoparticles with the desired and specific compositions, structures, arrangements, and physicochemical properties. In this report, we review the key principles guiding the formation and growth of nanoclusters, their evolution into nanoparticles, and the role and contribution of coatings. We describe a range of imaging methods for characterization of nanoparticles at atomic resolution and a range of spectroscopy methods for structural and physicochemical characterization of such nanoparticles. This chapter concludes with a short review of the emergent applications of nanoparticles in biosciences.

Self-assembling Rotavirus VP6 Nanoparticle Vaccines Expressed in Escherichia coli Elicit Systemic and Mucosal Responses in Mice

Background:

Rotavirus is the most common cause of infectious diarrhea in infants and young children around the world. The inner capsid protein VP6 has been discussed as alternative vaccine as it can induce cross-protective immune responses against different RV strai. The use of ferritin nanoparticle may enhance the immunogenicity of the subunit vaccine.

Objective:

In this article, our motivation is to design and obtain a self-assemble rotavirus nanoparticle vaccine which can induce efficiency immune response.

Methods:

The VP6 protein was fused with ferritin and expressed in the Escherichia coli expression system. The recombinant VP6-ferritin (rVP6-ferritin) protein was purified by His-tag affinity chromatography and fast protein liquid chromatography. Transmission electron micrographic analysis was used to detect the nanostructure of the self-assembled protein. Mice were gavage with the protein and ELISA was used to detect the titer of the VP6 specific antibody.

Results:

The recombined VP6-ferritin was expressed in the Escherichia coli as an inclusion body form and the purified protein has similar antigenicity to rotavirus VP6. Transmission electron micrographic analysis of rVP6-ferritin exhibited spherical architecture with a uniform size distribution, which is similar to the ferritin nanocage. Immune response analysis showed that mice immunized by rVP6-ferritin protein induced 8000 (8000±1093) anti-VP6 IgG titers or 1152 (1152±248.8) anti-VP6 IgA titers.

Conclusion:

According to the above research, the rotavirus VP6-ferritin protein can be easily express and self-assemble to the nano-vaccine and induce efficiency humoral and mucosal immunity. Our research makes a foundation for the development of oral rotavirus vaccine.

Modulating the physicochemical and structural properties of gold-functionalized protein nanotubes through thiol surface modification

Biomolecules are advantageous scaffolds for the synthesis and ordering of metallic nanoparticles. Rotavirus VP6 nanotubes possess intrinsic affinity to metal ions, a property that has been exploited to synthesize gold nanoparticles over them. The resulting nanobiomaterials have unique properties useful for novel applications. However, the formed nanobiomaterials lack of colloidal stability and flocculate, limiting their functionality. Here we demonstrate that it is possible to synthesize thiol-protected gold nanoparticles over VP6 nanotubes, which resulted in soluble nanobiomaterials. With this strategy, it was possible to modulate the size, colloidal stability, and surface plasmon resonance of the synthesized nanoparticles by controlling the content of the thiolated ligands. Two types of water-soluble ligands were tested, a small linear ligand, sodium 3-mercapto-1-propanesulfonate (MPS), and a bulky ligand, 5-mercaptopentyl β-D-glucopyranoside (GlcC5SH). The synthesized nanobiomaterials had a higher stability in suspension, as determined by Z-potential measurements. To the extent of our knowledge, this is the first time that a rational strategy is developed to modulate the particular properties of metal nanoparticles in situ synthesized over a protein bioscaffold through thiol coating, achieving a high spatial and structural organization of nanoparticles in a single integrative hybrid structure.

Characterization of conductive nanobiomaterials derived from viral assemblies by low-voltage STEM imaging and Raman scattering

New technologies require the development of novel nanomaterials that need to be fully characterized to achieve their potential. High-resolution low-voltage scanning transmission electron microscopy (STEM) has proven to be a very powerful technique in nanotechnology, but its use for the characterization of nanobiomaterials has been limited. Rotavirus VP6 self-assembles into nanotubular assemblies that possess an intrinsic affinity for Au ions. This property was exploited to produce hybrid nanobiomaterials by the in situ functionalization of recombinant VP6 nanotubes with gold nanoparticles. In this work, Raman spectroscopy and advanced analytical electron microscopy imaging with spherical aberration-corrected (Cs) STEM and nanodiffraction at low-voltage doses were employed to characterize nanobiomaterials. STEM imaging revealed the precise structure and arrangement of the protein templates, as well as the nanostructure and atomic arrangement of gold nanoparticles with high spatial sub-Angstrom resolution and avoided radiation damage. The imaging was coupled with backscattered electron imaging, ultra-high resolution scanning electron microscopy and x-ray spectroscopy. The hybrid nanobiomaterials that were obtained showed unique properties as bioelectronic conductive devices and showed enhanced Raman scattering by their precise arrangement into superlattices, displaying the utility of viral assemblies as functional integrative self-assembled nanomaterials for novel applications.

Understanding internalization of rotavirus VP6 nanotubes by cells: towards a recombinant vaccine

Rotavirus VP6 nanotubes are an attractive option for a recombinant vaccine against rotavirus disease. Protection against rotavirus infection and an adjuvant effect have been observed upon immunization with VP6 nanotubes. However, little information exists on how VP6 nanotubes interact with cells and trigger an immune response. In this work, the interaction between VP6 nanotubes and different cell lines was characterized. VP6 nanotubes were not cytotoxic to any of the animal or human cell lines tested. Uptake of nanotubes into cells was cell-line-dependent, as only THP1 and J774 macrophage cells internalized them. Moreover, the size and spatial arrangement of VP6 assembled into nanotubes allowed their uptake by macrophages, as double-layered rotavirus-like particles also displaying VP6 in their surface were not taken up. The internalization of VP6 nanotubes was inhibited by methyl-β-cyclodextrin, but not by genistein, indicating that nanotube entry is specific, depends on the presence of cholesterol in the plasma membrane, and does not require the activity of tyrosine kinases. The information generated here expands our understanding of the interaction of protein nanotubes with cells, which is useful for the application of VP6 nanotubes as a vaccine.

Effect of metal catalyzed oxidation in recombinant viral protein assemblies

Background

Protein assemblies, such as virus-like particles, have increasing importance as vaccines, delivery vehicles and nanomaterials. However, their use requires stable assemblies. An important cause of loss of stability in proteins is oxidation, which can occur during their production, purification and storage. Despite its importance, very few studies have investigated the effect of oxidation in protein assemblies and their structural units. In this work, we investigated the role of in vitro oxidation in the assembly and stability of rotavirus VP6, a polymorphic protein.

Results

The susceptibility to oxidation of VP6 assembled into nanotubes (VP6_NT) and unassembled VP6 (VP6_U) was determined and compared to bovine serum albumin (BSA) as control. VP6 was more resistant to oxidation than BSA, as determined by measuring protein degradation and carbonyl content. It was found that assembly protected VP6 from in vitro metal-catalyzed oxidation. Oxidation provoked protein aggregation and VP6_NT fragmentation, as evidenced by dynamic light scattering and transmission electron microscopy. Oxidative damage of VP6 correlated with a decrease of its center of fluorescence spectral mass. The in vitro assembly efficiency of VP6_U into VP6_NT decreased as the oxidant concentration increased.

Conclusions

Oxidation caused carbonylation, quenching, and destruction of aromatic amino acids and aggregation of VP6 in its assembled and unassembled forms. Such modifications affected protein functionality, including its ability to assemble. That assembly protected VP6 from oxidation shows that exposure of susceptible amino acids to the solvent increases their damage, and therefore the protein surface area that is exposed to the solvent is determinant of its susceptibility to oxidation. The inability of oxidized VP6 to assemble into nanotubes highlights the importance of avoiding this modification during the production of proteins that self-assemble. This is the first time that the role of oxidation in protein assembly is studied, evidencing that oxidation should be minimized during the production process if VP6 nanotubes are required.

Strategies for specifically directing metal functionalization of protein nanotubes: constructing protein coated silver nanowires

Biological molecules that self-assemble in the nanoscale range are useful multifunctional materials. Rotavirus VP6 protein self-assembles into tubular structures in the absence of other rotavirus proteins. Here, we present strategies for selectively directing metal functionalization to the lumen of VP6 nanotubes. The specific in situ metal reduction in the inner surface of nanotube walls was achieved by the simple modification of a method previously reported to functionalize the nanotube outer surface. Silver nanorods and nanowires as long as 1.5 μm were formed inside the nanotubes by coalescence of nanoparticles. Such one-dimensional structures were longer than others previously obtained using bioscaffolds. The interactions between silver ions and the nanotube were simulated to understand the conditions that allowed nanowire formation. Molecular docking showed that a naturally occurring arrangement of aspartate residues enabled the stabilization of silver ions on the internal surface of the VP6 nanotubes. This is the first time that such a spatial arrangement has been proposed for the nucleation of silver nanoparticles, opening the possibility of using such an array to direct functionalization of other biomolecules. These results demonstrate the natural capabilities of VP6 nanotubes to function as a versatile biotemplate for nanomaterials.

Simultaneous expression of recombinant proteins in the insect cell-baculovirus system: production of virus-like particles

The insect cell-baculovirus system (IC-BEVS) is widely used for the production of recombinant viral proteins for vaccine applications. It is especially suitable for the production of virus-like particles, which often require the simultaneous production of several recombinant proteins. Here, the available tools and process requirements for the simultaneous production of several recombinant proteins using the IC-BEVS are discussed. The production of double-layered rotavirus like particles is used as a specific example for the simultaneous production of two recombinant proteins. Methods to quantify VLP in small samples are described. The multiplicity and time of infection are presented as tools to manipulate protein concentration, and the effect on protein concentration ratios on the assembly efficiency of double-layered rotavirus like particles is discussed. It was found that not only the ratio between the recombinant proteins is determinant of VLP assembly efficiency, but also that assembly efficiency is related to the characteristics of the assembled proteins. This is the first time that kinetics of VLP production are followed during cultures, and that the assembly efficiency is quantitatively determined.