Tyrosine Phosphorylation of Bovine Herpesvirus 1 Tegument Protein VP22 Correlates with the Incorporation of VP22 into Virions

Abstract

Tyrosine phosphorylation has been shown to play a role in the replication of several herpesviruses. In this report, we demonstrate that bovine herpesvirus 1 infection triggered tyrosine phosphorylation of proteins with molecular masses similar to those of phosphorylated viral structural proteins. One of the tyrosine-phosphorylated viral structural proteins was the tegument protein VP22. A tyrosine 38-to-phenylalanine mutation totally abolished the phosphorylation of VP22 in transfected cells. However, construction of a VP22 tyrosine 38-tophenylalanine mutant virus demonstrated that VP22 was still phosphorylated but that the phosphorylation site may change to the C terminus rather than be in the N terminus as in wild-type VP22. In addition, the loss of VP22 tyrosine phosphorylation correlated with reduced incorporation of VP22 compared to that of envelope glycoprotein D in the mutant viruses but not with the amount of VP22 produced during virus infection. Our data suggest that tyrosine phosphorylation of VP22 plays a role in virion assembly.The tegument is a unique feature of herpesviruses and remains the least well-characterized virion compartment (41).There are approximately 15 virally encoded proteins that participate in the assembly of the amorphous tegument structure, and these tegument proteins occupy the majority of the mass in the virion (18,25,40). Recent studies have shown that at least a portion of the tegument structure has an ordered organization and interacts with the capsid (37,42,43,47,48); however, little is known regarding the acquisition of the viral tegument process (14,15,36,38,41). The incorporation of herpes simplex virus type 1 (HSV-1) tegument protein VP22 is increased more than twofold when the VP22 protein expression level is increased fivefold (21). This observation is consistent with the hypothesis that the incorporation of tegument protein is partly determined by local protein concentration. In contrast, the amount of HSV-1 tegument protein UL37 in virions is strictly controlled despite a 20-fold increase of UL37 in infected cells (25). Thus, multiple mechanisms to control the incorporation of different tegument proteins may exist. In addition, evidence suggests that acquisition of the tegument is independent of capsid or envelope (26, 36). The tegument retains its structural integrity in the absence of the capsid and envelope, indicating strong intermolecular interactions that must exist between these tegument proteins to support the seemingly amorphous structure (7,27,40).Most of the herpesvirus tegument proteins are phosphoproteins (3,11,12,20,41). Phosphorylation of tegument proteins is believed to play a role in tegument protein dissociation (28). Both cellular and virally encoded kinases are involved in the phosphorylation of tegument proteins (5, 11, 12), and serines of tegument protein HSV-1 VP22 are phosphorylated in infected cells (11,12). Phosphorylation of VP22 coincides with the translocation of VP22 into the nuclei of HSV-1-infected cells (10,19,28,32,33). Interestingly...

Phosphorylation of Bovine Herpesvirus 1 VP8 Plays a Role in Viral DNA Encapsidation and Is Essential for Its Cytoplasmic Localization and Optimal Virion Incorporation

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Molecular characterization of the pseudorabies virus UL2 gene

“…Phosphorylation site prediction (see Figure 3) revealed 12 potential phosphorylation sites in PRV UL2, including 3 serine, 8 threonine, and 1 tyrosine residues. Tyrosine phosphorylation is well known to be involved in the modification of protein translocation from the cytoplasm to the nucleus during productive viral infection (Pomeranz and Blaho, 1999) and the replication of several herpesviruses (Geiss et al, 2001;Ren et al, 2001). Phosphorylation of UDG at threonine is reported to be important for base excision repair (Lu et al, 2004), and various phosphoforms of threonine and serine sites of the non-catalytic domain confer distinct functional properties to UDG, such as protein turnover, different activities, association with replication protein A, and nuclear and mitochondrial genomic integrity (Caradonna and Muller-Weeks, 2001;Hagen et al, 2008).…”

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