Use of fusions to viral coat proteins as antigenic carriers for vaccine development

Selective in Situ Assembly of Viral Protein onto DNA Origami

Engineering hybrid protein-DNA assemblies in a controlled manner has attracted particular attention, for their potential applications in biomedicine and nanotechnology due to their intricate folding properties and important physiological roles. Although DNA origami has served as a powerful platform for spatially arranging functional molecules, in situ assembly of proteins onto DNA origami is still challenging, especially in a precisely controlled and facile manner. Here, we demonstrate in situ assembly of tobacco mosaic virus (TMV) coat proteins onto DNA origami to generate programmable assembly of hybrid DNA origami-protein nanoarchitectures. The protein nanotubes of controlled length are precisely anchored on the DNA origami at selected locations using TMV genome-mimicking RNA strands. This study opens a new route to the organization of protein and DNA into sophisticated protein-DNA nanoarchitectures by harnessing the viral encapsidation mechanism and the programmability of DNA origami.

Immunogenic display of diverse peptides on virus-like particles of RNA phage MS2

The high level of immunogenicity of peptides displayed in dense repetitive arrays on virus-like particles makes recombinant VLPs promising vaccine carriers. Here, we describe a platform for vaccine development based on the VLPs of RNA bacteriophage MS2. It serves for the engineered display of specific peptide sequences, but will also allow the construction of random peptide libraries from which specific binding activities can be recovered by affinity selection. Peptides representing the V3 loop of HIV gp120 and the ECL2 loop of the HIV coreceptor, CCR5, were inserted into a surface loop of MS2 coat protein. Both insertions disrupted coat VLP assembly, apparently by interfering with protein folding, but these defects were suppressed efficiently by genetically fusing coat protein's two identical polypeptides into a single-chain dimer. The resulting VLPs displayed the V3 and ECL2 peptides on their surfaces where they showed the potent immunogenicity that is the hallmark of VLP-displayed antigens. Experiments with random-sequence peptide libraries show the single-chain dimer to be highly tolerant of six, eight and ten amino acid insertions. MS2 VLPs support the display of a wide diversity of peptides in a highly immunogenic format, and they encapsidate the mRNAs that direct their synthesis, thus establishing the genotype/phenotype linkage necessary for recovery of affinity-selected sequences. The single-chain MS2 VLP therefore unites in a single structural platform the selective power of phage display with the high immunogenicity of VLPs.

Stability and assembly in vitro of bacteriophage PP7 virus-like particles

Background

The stability of a virus-like particle (VLP) is an important consideration for its use in nanobiotechnology. The icosahedral capsid of the RNA bacteriophage PP7 is cross-linked by disulfide bonds between coat protein dimers at its 5-fold and quasi-6-fold symmetry axes. This work determined the effects of these disulfides on the VLP's thermal stability.

Results

Measurements of the thermal denaturation behavior of PP7 VLPs in the presence and absence of a reducing agent show that disulfide cross-links substantially stabilize them against thermal denaturation. Although dimers in the capsid are linked to one another by disulfides, the two subunits of dimers themselves are held together only by non-covalent interactions. In an effort to confer even greater stability a new cross-link was introduced by genetically fusing two coat protein monomers, thus producing a "single-chain dimer" that assembles normally into a completely cross-linked VLP. However, subunit fusion failed to increase the thermal stability of the particles, even though it stabilized the isolated dimer. As a step toward gaining control of the internal composition of the capsid, conditions that promote the assembly of PP7 coat protein dimers into virus-like particles in vitro were established.

Conclusion

The presence of inter-dimer disulfide bonds greatly stabilizes the PP7 virus-like particle against thermal denaturation. Covalently cross-linking the subunits of the dimers themselves by genetically fusing them through a dipeptide linker sequence, offers no further stabilization of the VLP, although it does stabilize the dimer. PP7 capsids readily assemble in vitro in a reaction that requires RNA.

Preparation of His-tagged armored RNA phage particles as a control for real-time reverse transcription-PCR detection of severe acute respiratory syndrome coronavirus

Armored RNA has been increasingly used as both an external and internal positive control in nucleic acid-based assays for RNA virus. In order to facilitate armored RNA purification, a His6 tag was introduced into the loop region of the MS2 coat protein, which allows the exposure of multiple His tags on the surface during armored RNA assembly. The His-tagged armored RNA particles were purified to homogeneity and verified to be free of DNA contamination in a single run of affinity chromatography. A fragment of severe acute respiratory syndrome coronavirus (SARS-CoV) genome targeted for SARS-CoV detection was chosen for an external positive control preparation. A plant-specific gene sequence was chosen for a universal noncompetitive internal positive control preparation. Both controls were purified by Co2+ affinity chromatography and were included in a real-time reverse transcription-PCR assay for SARS-CoV. The noncompetitive internal positive control can be added to clinical samples before RNA extraction and enables the identification of potential inhibitive effects without interfering with target amplification. The external control could be used for the quantification of viral loads in clinical samples.

Bacteriophage MS2: molecular weight and spatial distribution of the protein and RNA components by small-angle neutron scattering and virus counting

Small-angle neutron scattering (SANS) has been used to extend the structural characterization of the MS2 phage by examining its physical characteristics in solution. Specifically, the contrast variation technique was employed to determine the molecular weight of the individual components of the MS2 virion (protein shell and genomic RNA) and the spatial relationship of the genomic RNA to its protein shell. A consequence of this work was to evaluate a novel particle counting instrument, the integrated virus detection system (IVDS) that, in combination with SANS, has the potential to provide rapid quantitative physical characterization of unidentified viruses and phage.