Structural and functional characterization of the bracovirus protein glc1.8
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Parasitoid wasps are insects that develop as parasites of other arthropods during their immature stages but are free living as adults. Some parasitoid wasps in the superfamily Ichneumonoidea rely on polydnaviruses (PDVs) to suppress the host immune system. Microplitis demolitor bracovirus (MdBV), which symbiotically associates with the braconid wasp Microplitis demolitor, has been studied with its genome sequenced and gene families identified. Among the identified genes, glc1.8 encodes for a glycoprotein which plays an essential role in blocking adhesion and phagocytosis of host hemocytes. In this study, I first identified that in the MdBV genome, there is another member of the glc gene family. I also determined that a cell line stably transfected with glc1.8 contains two forms of this gene: glc1.8 and a larger form of this gene designated glc1.82. The larger gene likely arose by recombination. Characterization of the glycans associated with Glc1.8 identified Man3NAc2 and Man3NAc2F as major constituents while functional studies indicated that glycosylation is essential for immunosuppressive activity. A C-terminal deletion mutant which has no cytoplasmic tail showed reduced activity, suggesting that Glc1.8 may interact with cytoplasmic factors in host cells. Lastly, I found that viral infection reduces transcript abundance of host integrins that are important for cell spreading.