The N and C Termini of the Coat Proteins of Potyviruses Are Surface-located and the N Terminus Contains the Major Virus-specific Epitopes

Abstract

SUMMARYMild proteolysis by trypsin of particles of six potyviruses (bean yellow mosaic virus, clover yellow vein virus, Johnson grass mosaic virus, passion-fruit woodiness virus, potato virus Y and watermelon mosaic virus II) revealed that the N-and C-terminal regions of their coat protein are exposed on the particles' surfaces. The enzyme treatment removed the N-terminal region (30 to 67 amino acids long, depending on the virus) and 18 to 20 amino acids from the C terminus of the coat proteins, leaving a fully assembled virus particle composed of coat protein cores consisting of 216 or 218 amino acid residues. These core particles were indistinguishable from untreated native particles in an electron microscope and were still infectious. The core particles lacked the virus-specific surface epitopes that are recognized by the bulk of the polyclonal antibodies raised against the whole virus particles. Epitopes thought to be groupspecific were located in the trypsin-resistant core protein region. The implications of these findings are discussed in relation to the similar surface location of the N-and Cterminal regions of the coat protein of other rod-shaped plant viruses and the observed common structural features displayed by isometric plant and animal viruses.

The Use of 3' Non-coding Nucleotide Sequences in the Taxonomy of Potyviruses: Application to Watermelon Mosaic Virus 2 and Soybean Mosaic Virus-N

“…Most of the differences (including a 16 residue deletion in SMV-N) occurred in the 45 N-terminal residues, with the remainder of the two coat protein molecules being very similar (92 ~ homology). This observation, that the 235 C-terminal amino acid residues are far more conserved than the surface-exposed, immunodominant N-terminal region (Shukla et al, 1988b), suggested that the 3' end of the potyvirus genome including the untranslated region may be an accurate marker of genetic relatedness.…”

Structures of plant viruses from vibrational circular dichroism

“…VCD has provided evidence for helical structures in all of the viruses and some b-sheet structures in PVX, NMV and PMV, but not in TMV. It has been suggested (Sawyer et al, 1987;Shukla et al, 1988; Blanch et al, 2002) that the coat protein folds of PVX and NMV may be similar to that of TMV, being based on the helix bundle, but with differences in detail resulting from differences in the appended loops and turns and from the extra sequences present in the potexviruses. These differences may be responsible for the observed VCD differences.…”

Identification of plant viruses using one-dimensional gel electrophoresis and peptide mass fingerprints

“…According to predicted CP masses of plant viruses (Blouin et al, 2009), most virus CPs have masses lower than Rubisco, although some fall within its mass range. Another consideration is that viral CPs can be resistant to trypsin digestion because of post-translational modification (Shukla et al, 1988), which may explain why coverage of tryptic fragments of viral CPs was relatively low (11-36%). It is worth noting that viral proteins other than CPs were not observed on the gels or detected by PMF, probably because they were in quantities below the resolution of the Coomassie stain used.…”