ИСТИНА

Potyviruses are the largest and most economically important group of plant viruses. Earlier we have reported that virions of Potyvirus Potato Virus A (PVA) to have a peculiar combination of physicochemical properties and its coat protein (CP) contained unstructured domains [1]. Structural analysis of the PVA CP in solution was performed by small angle X-ray scattering (SAXS), fluorescence spectroscopy and electron microscopy. Overall structural characteristics of PVA CP obtained by SAXS (radii of gyration, Porod volumes, molecular masses) clearly point to the formation of large particles containing dozens (~ 60) of the individual PVA CP macromolecules. Porod asymptotic and Kratky plot indicate the existence of rather compact dense particles at pH 7.8, and the presence of partly disordered bodies without clearly defined borders at pH 10.5. Ab initio shape reconstruction of the CP associates at pH 7.8 demonstrates cylindrical particles similar to the shape of Potato Virus A. These particles undergo dramatic changes with increasing pH to10.5: they lose their compactness and split into poorly connected spherical fragments. The results of the electron microscopy analysis show that PVA CP dialyzed at pH 7.8 is assembled into short cylindrical virus-like particles, while the loose structures obtained at pH 10.5 form spherical shapes with the size of about 20-30 nm. Fluorescence spectra of both intact PVA virion and isolated PVA CP at pH 7.8 have two maxima at 314 and ~330 nm, i.e. these two species have similar tertiary structure. Fluorescence spectrum of the isolated PVA CP in buffer with pH 10.5 has the only maximum -at 343 nm. This shift of the maximum position from 330 to 343 nm reflects the loss of the tertiary structure. Generally, the results of the present communication show that self-assembly of the isolated PVA CP in buffer with pH7.8 is the intrinsic biological property of the PVA coat protein needed for the formation of an viral envelope to protect genetic material of the virus. This work was supported by Russian Foundation BR (15-54-74002 EMBL, 15-04-01406, 16-03-00375). [1] Ksenofontov, AL, Paalme, V., Arutyunyan, AM. et al.(2013) PLoS ONE, 8, e67830.