Potato virus Y (PVY) is economically one of the most important plant viruses and the
most important viral pathogen of potato. Virus can cause enormous damage to
growing crops, with the PVYNTN strain being the most harmful as it causes potato
tuber necrotic ringspot disease.
PVY virions are around 740 nm long flexible filaments, assembled from around 2000
copies of the coat protein (CP) and viral RNA. The heterologous expression of CP in
bacterial cells produces virus-like particles (VLP), which are assembled from the CPs
in the absence of viral RNA. The detailed structure of flexible filamentous viruses
was not known until recently, when the revolutionary advances in cryo-electron
microscopy (cryo-EM) enabled determination of such viruses. During this research,
we used cryo-EM to determine spatial structure of the PVY at 3,4 Å resolution and of
the corresponding VLP at 4,1 Å resolution.
CPPVY is comprised of three structural regions: the globular core domain and
extended N- and C-terminal regions, which allow structural adaptations to different
binding partners and assembly into the filaments with the unique architecture.
Namely, CPPVY assemble in helical form around the viral RNA, while in the absence of
the viral RNA, the CPs assemble into octameric rings that stack together into long
VLP filaments. We analysed the role of N- and C-terminal regions in VLP assembly
and viral infectivity by deletion mutations of CP in VLP and virus. The biochemical
and biophysical characterization showed that the N-terminal region is crucial for VLP
assembly, while deletion of the C-terminal region had no negative impact on
filament assembly. On the other hand, the in planta experiments showed the
importance of both regions for the infectivity of the virus. The virus with the
deletion of 50 N-terminal amino acid residues on the CP (ΔN50-CP) is capable of
limited RNA replication but its movement is abolished. However, we showed that
C-terminal deletions of 40 or 60 amino acid residues on the CP (ΔC40-CP and
ΔC60-CP) basically completely hinder the viral RNA replication. In contrast to the ΔN
mutant, we could observe some VLP-like particles in the homogenate of plant leaves
infected with the cDNA of ΔC mutants.
Determination of the 3D structures of PVY and corresponding VLPs is a crucial basis
for the development of prevention strategies for plant protection and for the
development of nanobiotechnological applications based on VLPPVY.
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