Mapping of two O‐GlcNAc modification sites in the capsid protein of the potyvirus Plum pox virus

Abstract

A large number of O-linked N-acetylglucosamine (OGlcNAc) residues have been mapped in vertebrate proteins, however targets of O-GlcNAcylation in plants still have not been characterized. We show here that O-GlcNAcylation of the N-terminal region of the capsid protein of Plum pox virus resembles that of animal proteins in introducing O-GlcNAc monomers. Thr-19 and Thr-24 were specifically O-GlcNAcylated. These residues are surrounded by amino acids typical of animal O-GlcNAc acceptor sites, suggesting that the specificity of O-GlcNAc transferases is conserved among plants and animals. In laboratory conditions, mutations preventing O-GlcNAcylation of Thr-19 and Thr-24 did not have noticeable effects on PPV competence to infect Prunus persicae or Nicotiana clevelandii. However, the fact that Thr-19 and Thr-24 are highly conserved among different PPV strains suggests that their O-GlcNAc modification could be relevant for efficient competitiveness in natural conditions.

O-GlcNAc modification of the coat protein of the potyvirus Plum pox virus enhances viral infection

“…These data do not allow us to discriminate whether these threonines are indeed O -GlcNAc modified or if they are important for modification of neighboring residues. However, ETD MS/MS analysis confirmed that, in addition to the previously identified O -GlcNAcylation sites at T19 and T24 (Pérez et al, 2006), the CP of virions is O -GlcNAc modified at T41, T53 and T54 and/or T58, which is in good agreement with the mutagenesis analysis. In addition, S65, which was not mutated, was also shown to be O -GlcNAc-modified.…”

“…1) and a mutagenesis analysis identified threonines T19 and T24 as the modified residues (Pérez et al, 2006). Mutational mapping using a heterologous E. coli system indicated that in addition to modifying T19 and T24 SEC also modified T41 and S43 (Scott et al, 2006).…”

“…Genetic studies suggest that SEC but not SPY modifies PPV CP (Chen et al, 2005). Thr19 and Thr24 have been identified as two of the PPV CP residues that are O -GlcNAc-modified in virions purified from infected plants (Pérez et al, 2006) and O -GlcNAcylation of these two residues as well as three other residues, Thr41, Thr53, Ser65, by SEC was demonstrated using a heterologous Escherichia coli -based co-expression system (Scott et al, 2006; Kim et al, 2011). Several proteins from different animal and human viruses have been shown to be O -GlcNAcylated (Benko et al, 1988; Caillet-Boudin et al, 1989; Mullis et al, 1990; Gonzalez and Burrone, 1991; Whitford and Faulkner, 1992; Greis et al, 1994; Medina et al, 1998), but there is little information about the relevance of O -GlcNAc modification for viral infections.…”

O-GlcNAc protein modification in plants: Evolution and function

“…The former seems to be the case because SEC O-GlcNAc modifies the capsid protein when they are co-expressed in E. coli [55]. The same amino acids that are modified by SEC in E. coli are modified in arabidopsis [55, 56]. Each modification to capsid protein from plants is a GlcNAc monomer indicating that SEC and animal OGTs make the same modification.…”

“…It is not clear if the defects in infection are a direct effect of the defect in modification of the capsid and/or a defect in the modification of a plant protein. One study where the known modification sites were mutated to non-modifiable amino acids did not impair infection [56], but it is possible that not all of the modified sites have been identified.…”