The Bombyx mori nucleopolyhedrovirus Bm111 affects virulence but not virus replication

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

Polyhedra can encapsulate other proteins and have potential applications as protein stabilizers. The extremely stable polyhedra matrix may provide a platform for future engineered micro-crystal devices. However, the protein composition of the polyhedra matrix remains largely unknown. In this study, the occlusion-derived virus (ODV)-removed BmNPV polyhedra matrix fraction was subjected to SDS-PAGE and then an LC-ESI-MS/MS analysis using a Thermo Scientific Q Exactive mass spectrometer. In total, 28 host and 91 viral proteins were identified. The host components were grouped into one of six categories, i.e., chaperones, ubiquitin and related proteins, host helicases, cytoskeleton-related proteins, RNA-binding proteins and others, according to their predicted Pfam domain(s). Most viral proteins may not be essential for polyhedra assembly, as evidenced by studies in the literature showing that polyhedra formation occurs in the nucleus upon the disruption of individual genes. The structural role of these proteins in baculovirus replication will be of significant interest in future studies. The immobilization of enhanced green fluorescent protein (eGFP) into the polyhedra by fusing with the C-terminus of BM134 that is encoded by open reading frame (ORF) 134 suggested that the polyhedra had a powerful capacity to trap foreign proteins, and BM134 was a potential carrier for incorporating proteins of interest into the polyhedra.

Identification and Characterization of BmVta1, a Bombyx mori (Lepidoptera: Bombycidae) Homologue for Vta1 That is Up-Regulated in Development

Vps20-associated 1 (Vta1) positively regulates Vacuolar protein sorting 4 (Vps4) to disassemble endosomal sorting complex required for transport III (ESCRT-III) for repeated uses in multivesicular body (MVB) pathway, virus budding and other processes. Currently, these proteins have mainly been studied in yeast and mammalian cells, while identities of them in insects remain largely unknown. We previously identified BmVps4, a Vps4 homologue from Bombyx mori. Here, we report the identification of a homologue for Vta1, designated as BmVta1. The BmVta1 cDNA contains an open reading frame of 933 bp and encodes a protein of 311 amino acid residues. We cloned BmVta1, expressed it in Escherichia coli, and prepared mouse polyclonal antibodies. Like BmVps4, BmVta1 is well conserved as shown by sequence analysis. Both proteins are localized in cytoplasm as revealed by subcellular location analysis. Interestingly, as revealed by semi-quantitative reverse transcription polymerase chain reaction (sqRT-PCR), transcriptions of BmVta1 and BmVps4 are highly up-regulated during silkworm metamorphosis and embryogenesis but down-regulated during larva stages, and are of higher levels in head, silk gland and testis than in Malpighian tube, fat body and ganglion, indicating important and similar roles of them in silkworm development and in silkworm tissues and organs. However, compared to BmVps4, the transcription of BmVta1 changes less drastically during development and is of much higher levels in midgut, ovary and hemolymph, suggesting the existence of distinct requirements of them in silkworm development and in certain tissues and organs.

A DNA Binding Protein Is Required for Viral Replication and Transcription in Bombyx mori Nucleopolyhedrovirus

A DNA-binding protein (DBP) [GenBank accession number: M63416] of Bombyx mori nuclear polyhedrosis virus (BmNPV) has been reported to be a regulatory factor in BmNPV, but its detailed functions remain unknown. In order to study the regulatory mechanism of DBP on viral proliferation, genome replication, and gene transcription, a BmNPV dbp gene knockout virus dbp-ko-Bacmid was generated by the means of Red recombination system. In addition, dbp-repaired virus dbp-re-Bacmid was constructed by the means of the Bac to Bac system. Then, the Bacmids were transfected into BmN cells. The results of this viral titer experiment revealed that the TCID50 of the dbp-ko-Bacmid was 0; however, the dbp-re-Bacmid was similar to the wtBacmid (p>0.05), indicating that the dbp-deficient would lead to failure in the assembly of virus particles. In the next step, Real-Time PCR was used to analyze the transcriptional phases of dbp gene in BmN cells, which had been infected with BmNPV. The results of the latter experiment revealed that the transcript of dbp gene was first detected at 3 h post-infection. Furthermore, the replication level of virus genome and the transcriptional level of virus early, late, and very late genes in BmN cells, which had been transfected with 3 kinds of Bacmids, were analyzed by Real-Time PCR. The demonstrating that the replication level of genome was lower than that of wtBacmid and dbp-re-Bacmid (p<0.01). The transcriptional level of dbp-ko-Bacmid early gene lef-3, ie-1, dnapol, late gene vp39 and very late gene p10 were statistically significantly lower than dbp-re-Bacmid and wtBacmid (p<0.01). The results presented are based on Western blot analysis, which indicated that the lack of dbp gene would lead to low expressions of lef3, vp39, and p10. In conclusion, dbp was not only essential for early viral replication, but also a viral gene that has a significant impact on transcription and expression during all periods of baculovirus life cycle.