Ubiquitins of Bombyx mori nucleopolyhedrovirus and Helicoverpa armigera nucleopolyhedrovirus show distinct subcellular localization in infected cells

Abstract

Ubiquitin (UB) is a conserved protein that regulates a number of processes in eukaryotic cells. Nearly all lepidopteran baculoviruses encode UB homologs showing a partial sequence identity with human UB (Hu-UB). In this study, the sequence, predicted 3D-structure and subcellular localization of UB homologs encoded by two different nucleopolyhedroviruses of Bombyx mori (BmNPV) and Helicoverpa armigera (HaNPV) were compared. UBs of BmNPV and HaNPV (Bm-UB, Ha-UB, respectively) shared only 73% of sequence identity of the different aa in relation to Hu-UB being localized in non-conserved parts, namely in two heterogeneous regions of aa 15-32 and aa 53-60. Interestingly, Bm-UB and Ha-UB share the same seven lysines except for an additional Lys54 in Bm-UB. However, in spite of the sequence heterogeneity, Bm-UB and Ha-UB have a similar predicted 3D-structure. A difference in their subcellular localization during virus growth in insect cell lines was found in the late stage of formation of occlusion-derived virus (ODV). In particular Bm-UB was localized mainly and evenly in the nucleus, while Ha-UB on the nuclear membrane. These data suggest that (i) UBs, besides being engaged in various cellular processes, have a role in specific processes of virus growth, and (ii) Bm-UB and Ha-UB may show certain different activities associated with the virus growth.

Protein composition analysis of polyhedra matrix of Bombyx mori nucleopolyhedrovirus (BmNPV) showed powerful capacity of polyhedra to encapsulate foreign proteins

“…ORF26 in the BmNPV genome encodes a ubiquitin homolog protein. During the very late stage of polyhedra formation, the BmNPV ubiquitin is largely and evenly localized in the nucleus, and in the cytoplasm, it exhibits a dotted distribution 37 . The identification of host and viral ubiquitins (Tables 1 and 2 ) prompted the question of whether certain proteins that are associated with the BmNPV polyhedra matrix were ubiquitylated.…”

“…Ubiquitin exists in several linked forms, and each form plays distinct roles in the cell. Although BmNPV ubiquitin contains an additional and seven conserved lysines 37 , two linked forms, i.e., K48- and K63-linked poly-ubiquitin chains, were identified, whereas for the host ubiquitin, K6-, K11-, K29-, K48- and K63-linked forms were observed (Table 3 ). Notably, the identification and role exploration of these ubiquitinated proteins in baculovirus replication will be of interest in future investigations.…”