Abstract
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.
Highlights
The architecture of viral capsids is largely based on either icosahedral or helical symmetry [1]
The Barley stripe mosaic virus (BSMV) coat protein (CP) absorption spectrum was measured in 3M LiCl solution immediately after disassembly of the virions and RNA precipitation, which occurs under these conditions [11], was typical for proteins of plant virus, showing that the protein was efficiently separated from the viral RNA
Formation of ribonucleoprotein complexes (RNPs) comprising viral genomic RNA and virus-encoded proteins is essential for many steps in plant virus life cycle, such as protection of viral genome from attacks by cellular enzymes, transport of viral RNA cell-to-cell and long distance through the phloem, and interaction with different virus-encoded and cell partner proteins
Summary
The architecture of viral capsids is largely based on either icosahedral or helical symmetry [1]. Further progress in TMV structural analysis was made about three decades later when higher resolutions were achieved by both X-ray fiber diffraction studies (2.9 A ) [7] and cryoelectron microscopy (4.6 A ) [8,9]. It should be noted, that such a resolution, even if some contradictions between the structures obtained by these two methods are not considered, is not sufficient to decipher the fine mechanisms of TMV self-assembly. The TMV CP structure includes two small a-helices located at the borders of the four-helix-bundle domain and a short b-strand of several residues Both N- and C-terminal protein regions exposed on the outer surface of the TMV capsid [7]. The internal surface of the TMV virion, where adjacent subunits are packed very tightly, has a complex structure consisting of a series of H-bond stabilized reverse turns [7]
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