N‐Terminal segment of potato virus X coat protein subunits is glycosylated and mediates formation of a bound water shell on the virion surface

Abstract

The primary structures of N-terminal 19-mer peptides, released by limited trypsin treatment of coat protein (CP) subunits in intact virions of three potato virus X (PVX) isolates, were analyzed. Two wild-type PVX strains, Russian (Ru) and British (UK3), were used and also the ST mutant of UK3 in which all 12 serine and threonine residues in the CP N-terminal segment were replaced by glycine or alanine. With the help of direct carbohydrate analysis and MS, it was found that the acetylated N-terminal peptides of both wildtype strains are glycosylated by a single monosaccharide residue (galactose or fucose) at NAcSer in the first position of the CP sequence, whereas the acetylated N-terminal segment of the ST mutant CP is unglycosylated. Fourier transform infrared spectra in the 1000-4000 cm )1 region were measured for films of the intact and in situ trypsindegraded PVX preparations at low and high humidity. These spectra revealed the presence of a broad-band in the region of valent vibrations of OH bonds (3100-3700 cm )1 ), which can be represented by superposition of three bands corresponding to tightly bound, weakly bound, and free OH groups. On calculating difference (ÔwetÕ minus ÔdryÕ) spectra, it was found that the intact wild-type PVX virions are characterized by high water-absorbing capacity and the ability to order a large number of water molecules on the virus particle. This effect was much weaker for the ST mutant and completely absent in the trypsin-treated PVX. It is proposed that the surface-located and glycosylated N-terminal CP segments of intact PVX virions induce the formation of a columnar-type shell from bound water molecules around the virions, which probably play a major role in maintaining the virion surface structure.

Potato virus X: structure, disassembly and reconstitution

“…(1994), who found that CPs of several natural PVX strains tested contained the carbohydrate material. The exact nature and location of the sugars was determined by modern mass‐spectrometry methods (Baratova et al ., 2004). It was found that the CP of Russian and UK3 strains of PVX contain about equal amounts of single galactose or fucose residues O‐linked to the same site at the acetylated N‐terminal serine residue of the PVX CP molecule.…”

Lectin-Mediated Resistance Impairs Plant Virus Infection at the Cellular Level

“…The most attractive hypothesis is that JAX1 and RTM1 can recognize a glycosylated viral protein because lectins recognize glycosylated proteins in animal innate immune systems (Fujita, 2002). Indeed, the N-terminal region of CP encoded by PVX, a potexvirus whose infection is inhibited by JAX1, is glycosylated (Baratova et al, 2004). Moreover, the CP N-terminal region of Plum pox virus, which is a Potyvirus affected by RTM1-mediated resistance (Decroocq et al, 2006), is also glycosylated in virus-infected cells (Ferná ndez-Ferná ndez et al, 2002).…”

Structure of Flexible Filamentous Plant Viruses

“…The virion was shown to have a deeply grooved surface. Fourier transform infrared spectroscopy studies of PVX suggest that the virion surface is highly hydrated and that the bound water molecules help to maintain the surface structure of the virion (6). Spectroscopic studies show that coat proteins of potexviruses and potyviruses have similarly high ␣-helical contents (5,31).…”