Qualitative proteomic analysis of Tipula oleracea nudivirus occlusion bodies

Nudiviruses are arthropod-specific large double-stranded circular DNA viruses, related to baculoviruses, which replicate in the nucleus of the cells they infect. To date, six fully sequenced nudiviral genomes are available in databases, and the protein profile from nudivirus particles was mainly characterized by PAGE. However, only a few direct matches have been completed between genomic and proteomic data, with the exception of the major occlusion body protein from Penaeus monodon nudivirus and four nucleocapsid proteins from Helicoverpa zea nudivirus-2. The function of predicted nudiviral proteins is still inferred from what is known from baculoviruses or endogenous nudiviruses (i.e. bracoviruses). Tipula oleracea nudivirus (ToNV) is the causative agent of crane fly nucleopolyhedrosis. Along with Penaeus monodon nudivirus, ToNV is the second fully sequenced nudivirus to be described as forming occlusion bodies. The protein profile revealed by Coomassie-stained SDS-PAGE is very similar to those observed for other nudiviruses, with five major protein bands of about 75, 48, 35, 25 and 12 kDa. Proteomic analysis, using on-line nanoflow liquid chromatography in tandem with high-resolution mass spectrometry, revealed that ToNV occlusion bodies are composed of 52 viral proteins, the most abundant of which are the functional homologue of baculovirus polyhedrin/granulin and the homologues of three Helicoverpa zea nudivirus-2 predicted proteins: the two virion structural proteins 34K (Hz2V052, the baculovirus capsid protein VP39 homologue) and 11K (Hz2V025), and the hypothetical protein Hz2V079, a newly identified nudivirus core gene product.