Characterization of the interaction between Varicella-Zoster virus (VZV) ORF9 protein and the major transactivator IE62

Abstract

In Varicella-zoster virus (VZV) the most expressed protein during infection is ORF9p. This protein is conserved in all the Alphaherpesvirus and is an essential tegument protein. ORF9p interacts with IE62 the major VZV transactivator which is also part of the tegument although the mechanisms leading to its incorporation into the particle are poorly understood. Considering that both proteins are present in high quantity in the viral tegument, it is suggested that one of the ORF9p functions is the recruitment of IE62 in order to be incorporated into the tegument (Cilloniz et al., 2007). Previous studies done in the laboratory prove that ORF9p plays an important role during secondary envelopment and viral particle formation. It is suggested that this main function is regulated by its phosphorylation and the interaction with other viral proteins (Riva et al., 2013). The first goal of this work is to determine if the phosphorylation of ORF9p is important for the interaction with IE62. The second aim is to determine the responsible site of ORF9p for the interaction with IE62 and glycoprotein gE. The role of ORF9p phosphorylation in the interaction with IE62 has been analysed using different ORF9p mutants lacking a phosphorylation by the ORF47 viral kinase. On one hand, we have demonstrated that the interaction between ORF9p and IE62 does not depend on the ORF9p phosphorylation level. On the other hand, we observe a co-localisation of both proteins accumulate in subcellular structures that accumulates in the vicinity of the nucleus and whose nature has still to be determined. More broadly, using mutants unable to express ORF47p and/or ORF66p, the two ser/thr kinases encoded by the virus or-phosphatase treatments, we showed that nor the phosphorylation of ORF9p or IE62 was important for their interaction. In a second part, we evaluate the importance of an WW domain present ORF9p sequence and shown to be important for HSV-1 VP22 (ORF9p homologue) interaction with VP16 the major transactivator. ORF9p punctual mutants were created by mutating the two tryptophan and the phenylalanine described to be important in HSV-1. Interestingly, F181A and W201F mutations present a loss of infection over time. Therefore, these two amino acids are perhaps important for the interaction with IE62 and gE. These observations confirm that nor the phosphorylation of ORF9p and IE62 or the amino acids F181 and W201 of ORF9p, located in a putative WW domain are not important for the interaction between these 2 tegument proteins.