Some properties of hybrid viruses reassembled in vitro

Surface Functionalization of Rod-Shaped Viral Particles for Biomedical Applications

While synthetic nanoparticles play a very important role in modern medicine, concerns regarding toxicity, sustainability, stability, and dispersity are drawing increasing attention to naturally derived alternatives. Rod-shaped plant viruses and virus-like particles (VLPs) are biological nanoparticles with powerful advantages such as biocompatibility, tunable size and aspect ratio, monodispersity, and multivalency. These properties facilitate controlled biodistribution and tissue targeting for powerful applications in medicine. Ongoing research efforts focus on functionalizing or otherwise engineering these structures for a myriad of applications, including vaccines, imaging, and drug delivery. These include chemical and biological strategies for conjugation to small molecule chemical dyes, drugs, metals, polymers, peptides, proteins, carbohydrates, and nucleic acids. Many strategies are available and vary greatly in efficiency, modularity, selectivity, and simplicity. This review provides a comprehensive summary of VLP functionalization approaches while highlighting biomedically relevant examples. Limitations of current strategies and opportunities for further advancement will also be discussed.

Chimeric Virus as a Source of the Potato Leafroll Virus Antigen

Large quantities of potato leafroll virus (PLRV) antigen are difficult to obtain because this virus accumulates in plants at a low titer. To overcome this problem, we constructed a binary vector containing chimeric cDNA, in which the coat protein (CP) gene of the crucifer infecting tobacco mosaic virus (crTMV) was substituted for the coat protein gene of PLRV. The PLRV movement protein (MP) gene, which overlaps completely with the CP gene, was doubly mutated to eliminate priming of the PLRV MP translation from ATG codons with no changes to the amino acid sequence of the CP. The untranslated long intergenic region located upstream of the CP gene was removed from the construct. Transcribed powerful tobamovirus polymerase of the produced vector synthesized PLRV CP gene that was, in turn, translated into the protein. CP PLRV packed RNAs from the helical crTMV in spherical virions. Morphology, size and antigenic specificities of the wild-type and chimeric virus were similar. The yield of isolated chimera was about three orders higher than the yield of native PLRV. The genetic manipulations facilitated the generation of antibodies against the chimeric virus, which recognize the wild-type PLRV.

Structural lability of Barley stripe mosaic virus virions

Virions of Barley stripe mosaic virus (BSMV) were neglected for more than thirty years after their basic properties were determined. In this paper, the physicochemical characteristics of BSMV virions and virion-derived viral capsid protein (CP) were analyzed, namely, the absorption and intrinsic fluorescence spectra, circular dichroism spectra, differential scanning calorimetry curves, and size distributions by dynamic laser light scattering. The structural properties of BSMV virions proved to be intermediate between those of Tobacco mosaic virus (TMV), a well-characterized virus with rigid rod-shaped virions, and flexuous filamentous plant viruses. The BSMV virions were found to be considerably more labile than expected from their rod-like morphology and a distant sequence relation of the BSMV and TMV CPs. The circular dichroism spectra of BSMV CP subunits incorporated into the virions, but not subunits of free CP, demonstrated a significant proportion of beta-structure elements, which were proposed to be localized mostly in the protein regions exposed on the virion outer surface. These beta-structure elements likely formed during virion assembly can comprise the N- and C-terminal protein regions unstructured in the non-virion CP and can mediate inter-subunit interactions. Based on computer-assisted structure modeling, a model for BSMV CP subunit structural fold compliant with the available experimental data was proposed.

Isolation and analysis of virus-specific ribonucleoprotein of tobacco mosaic virus-infected tobacco

A ribonucleoprotein fraction (vRNP) of a characteristic buoyant density greater than the buoyant density of tobacco mosaic virus (TMV) particles has been isolated from infected tissue by Cs2SO4 density gradient centrifugation. The vRNP particles appear to be TMV specific because they are synthesized in the presence of actinomycin D and have RNAs identified as genomic and I-class subgenomic (apparent Mr 1.1-1.3 x 106 and 0.60.8 x 10(6)) RNAs by their electrophoretic mobility and hybridization to plasmid-bearing RNA sequences. Polypeptides of apparent molecular weights 17,500 (TMV coat), 31,000, 37,000, and 39,000 were major constituents of vRNP. Of the minor polypeptides, those of apparent molecular weights 70,000, 68,000, 55,000, and 25,000 had electrophoretic mobilities similar to mobilities of polypeptides found in a ribonucleoprotein preparation from uninoculated plants. vRNP from common TMV-infected plants, but not from plants infected with a mutant that did not form native coat protein, reacted with immunoglobins against TMV and TMV coat protein. Common TMV and its vRNP differed in the extent of reactivity toward the two immunoglobins, in electron microscopic appearance, and in the higher sensitivity of vRNP to ribonuclease.

Stimulation by aurintricarboxylic acid of tobacco mosaic virus-specific RNA synthesis and production of informosome-like infection-specific ribonucleoprotein

It was shown that aurintricarboxylic acid (ATA), a well-known inhibitor of protein synthesis, markedly stimulates the synthesis of tobacco mosaic virus (TMV)-specific RNA species of the intermediate (I) class (apparent molecular weights 1.1-1.3 x 10(6) and 0.6-0.8 x 10(6)). No stimulation by ATA of full-length genomic TMV RNA or the subgenomic TMV RNA coding for TMV coat protein was detected. Informosome-like infection-specific ribonucleoprotein (vRNP) particles different from mature TMV particles were found in the TMV-infected cells (Yu. L. Dorokhov, N. M. Alexandrova, N. A. Miroshnichenko, and J. G. Atabekov, 1983, Virology 127, 237-252). It is shown here that [3H]uridine incorporation into vRNP RNAs was markedly stimulated in the presence of ATA. vRNP can be released from the TMV-specific polyribosomes by EDTA treatment, which suggests that it is involved in the translation process. The results of the pulse-chase experiments (including those in which TMV RNA synthesis is blocked by 2-thiouracil) suggest that vRNP does not serve as a precursor for mature virion.

Structure of the U2 strain of tobacco mosaic virus refined at 3.5 A resolution using X-ray fiber diffraction

The structure of the U2 strain of tobacco mosaic virus (TMV) has been determined by fiber diffraction methods at 3.5 A resolution, and refined by a combination of restrained least-squares and molecular dynamics methods to an R-factor of 0.096. The structure is extremely similar to that of the common strain of TMV, with the largest differences being in the protein loop that makes up the inner surface of the virus, and in the C-terminal region on the outer surface. Differences in the inner loop can be correlated with differences in the properties of the two viruses.

Tobacco rattle virus RNA-protein interactions

For the purpose of attempting to generalize the rules concerning morphogenesis of helical viruses, the in vitro reconstitution of the CAM strain of TRV was studied. The conditions for reconstitution and the importance of the aggregation state of the protein for initiation and elongation are compared with those of TMV. The initiation step consisting of the binding of RNA with the 36S disk of protein was easily accomplished. The polarity and the specificity of encapsidation of TRV RNA by homologous and heterologous viral protein is discussed.

Sequence of a specifically encapsidated RNA fragment originating from the tobacco-mosaic-virus coat-protein cistron

When 25-S tobacco mosaic virus (TMV) protein aggregate and TMV RNA, which has been partially digested by T1 RNase, are mixed under conditions suitable for reconstitution, only a few RNA fragments are encapsidated. These fragments were isolated and purified by polyacrylamide gel electrophoresis. The sequence of the three main fragments, the longest of which (fragment 1) was estimated to contain 103 nucleotides, has been determined. The two smaller fragments are portions of the longer chain produced by an additional specific scission. Because of the great affinity of 25-S TMV protein for this nucleotide sequence, it will be referred to as the "specifically encapsidated RNA fragment". The occurrence of a "hidden break" in the sequence has been demonstrated: fragment 1, purified by electrophoresis on a polyacrylamide gel without 8 M urea, gives rise upon further electroporesis in the presence of urea to two new bands corresponding to the two halves of the molecule. A stable hair-pin secondary structure has been derived from the base sequence which can account for the specificity of action of the enzyme. Because of its properties, we have suggested elsewhere that the sequence of fragment 1 might correspond to the disk recognition site for reconstitution, which is known to be located at the 5' end of the intact RNA. But experiments with TMV RNA whose 5'-OH end has been radioactively phosphorylated with polynucleotide kinase show that this is not the case. Analysis of the amino acid coding capacity of the fragment has instead revealed that fragment 1 is a portion of the TMV coat protein cistron.