Effect of the Coat Protein N-Terminal Domain Structure on the Structure and Physicochemical Properties of Virions of Potato Virus X and Alternanthera Mosaic Virus.

The amino acid sequences of the coat proteins (CPs) of the potexviruses potato virus X (PVX) and alternanthera mosaic virus (AltMV) share ~40% identity. The N-terminal domains of these proteins differ in the amino acid sequence and the presence of the N-terminal fragment of 28 residues (ΔN peptide) in the PVX CP. Here, we determined the effect of the N-terminal domain on the structure and physicochemical properties of PVX and AltMV virions. The circular dichroism spectra of these viruses differed significantly, and the melting point of PVX virions was 10-12°C higher than that of AltMV virions. Alignment of the existing high-resolution 3D structures of the potexviral CPs showed that the RMSD value between the Cα-atoms was the largest for the N-terminal domains of the two compared models. Based on the computer modeling, the ΔN peptide of the PVX CP is fully disordered. According to the synchrotron small-angle X-ray scattering (SAXS) data, the structure of CPs from the PVX and AltMV virions differ; in particular, the PVX CP has a larger portion of crystalline regions and, therefore, is more ordered. Based on the SAXS data, the diameters of the PVX and AltMV virions and helix parameters in solution were calculated. The influence of the conformation of the PVX CP N-terminal domain and its position relative to the virion surface on the virion structure was investigated. Presumably, an increased thermal stability of PVX virions vs. AltMV is provided by the extended N-terminal domain (ΔN peptide, 28 amino acid residues), which forms additional contacts between the adjacent CP subunits in the PVX virion.

Vaccine Candidate Against COVID-19 Based on Structurally Modified Plant Virus as an Adjuvant.

A recombinant vaccine candidate has been developed based on the major coronaviruses' antigen (S protein) fragments and a novel adjuvant-spherical particles (SPs) formed during tobacco mosaic virus thermal remodeling. The receptor-binding domain and the highly conserved antigenic fragments of the S2 protein subunit were chosen for the design of recombinant coronavirus antigens. The set of three antigens (Co1, CoF, and PE) was developed and used to create a vaccine candidate composed of antigens and SPs (SPs + 3AG). Recognition of SPs + 3AG compositions by commercially available antibodies against spike proteins of SARS-CoV and SARS-CoV-2 was confirmed. The immunogenicity testing of these compositions in a mouse model showed that SPs improved immune response to the CoF and PE antigens. Total IgG titers against both proteins were 9-16 times higher than those to SPs. Neutralizing activity against SARS-CoV-2 in serum samples collected from hamsters immunized with the SPs + 3AG was demonstrated.

Thermal remodelling of Alternanthera mosaic virus virions and virus-like particles into protein spherical particles.

The present work addresses the thermal remodelling of flexible plant viruses with a helical structure and virus-like particles (VLPs). Here, for the first time, the possibility of filamentous Alternanthera mosaic virus (AltMV) virions' thermal transition into structurally modified spherical particles (SP) has been demonstrated. The work has established differences in formation conditions of SP from virions (SPV) and VLPs (SPVLP) that are in accordance with structural data (on AltMV virions and VLPs). SP originate from AltMV virions through an intermediate stage. However, the same intermediate stage was not detected during AltMV VLPs' structural remodelling. According to the biochemical analysis, AltMV SPV consist of protein and do not include RNA. The structural characterisation of AltMV SPV/VLP by circular dichroism, intrinsic fluorescence spectroscopy and thioflavin T fluorescence assay has been performed. AltMV SPV/VLP adsorption properties and the availability of chemically reactive surface amino acids have been analysed. The revealed characteristics of AltMV SPV/VLP indicate that they could be applied as protein platforms for target molecules presentation and for the design of functionally active complexes.

Structure and properties of virions and virus-like particles derived from the coat protein of Alternanthera mosaic virus.

Plant viruses and their virus-like particles (VLPs) have a lot of advantages for biotechnological applications including complete safety for humans. Alternanthera mosaic virus (AltMV) is a potentially promising object for design of novel materials. The 3D structures of AltMV virions and its VLPs were obtained by single particle EM at ~13Å resolution. The comparison of the reconstructions and a trypsin treatment revealed that AltMV CPs possesses a different fold in the presence (virions) and absence of viral RNA (VLPs). For the first time, the structure of morphologically similar virions and virus-like particles based on the coat protein of a helical filamentous plant virus is shown to be different. Despite this, both AltMV virions and VLPs are stable in a wide range of conditions. To provide a large amount of AltMV for biotechnology usage the isolation procedure was modified.