Influence of the structure of the coat protein N-terminal segment in potato virus X and alternanthera mosaic virus on the structure and physico-chemical properties of virions

Abstract

The amino acid sequences of coat proteins (CPs) of potexviruses such as potato virus X (PVX) and alternanthera mosaic virus (AltMV) share about 40% sequence identity. However, the N-terminal CP domains of these virions differ both in length (the N-terminal CP domain of PVX is longer by 28 residues, ∆N = 28), and in amino acid sequence. In this work, we determined the effect of the N-terminal CP domain on the structure and physicochemical properties of the entire PVX and AltMV virions. It was shown that the melting point of PVX samples is 10-12°C higher than that of AltMV preparations; the circular dichroism spectra of these viruses also differ significantly. Spatial alignment of the existing high-resolution potexvirus CP structures showed that the RMSD value between Cα-atoms was the largest for the N-terminal domains of the two compared models. From computer simulations the ∆N-terminal CP domain of PVX is completely disordered. According to synchrotron small-angle X-ray scattering (SAXS) data, the structure of CP of PVX and AltMV virions differs, in particular, CP PVX has a larger size of crystallinity regions and, therefore, is more ordered. Using SAXS, virion diameters and helix parameters in solution are calculated. The influence of the conformation and localization of the N-terminal domain of PVX CP relative to the surface of the virion on its structure was revealed. Presumably, the increased thermal stability of PVX virions compared to AltMV is provided by the elongated N-terminal domains (ΔN = 28), which ensures additional contact between the adjacent CP subunits in the PVX virion.