Tetramerization of white spot syndrome virus envelope protein VP33 and its interaction with VP24

Complete genome of the new bacilliform virus that causes Milky Hemolymph Syndrome in Chionoecetes bairdi (Rathbun, 1924)

The genome of a new member of the Nimaviridae family has been sequenced. The Chionoecetes bairdi bacilliform virus (CbBV) causes Milky Hemolymph Syndrome (MHS) in Chionoecetes bairdi populations of the Pacific coast of Kamchatka. The CbBV genome is represented by double-stranded DNA with a length of 245,567 nucleotides containing 120 ORFs. Of these, 85 proteins had significant matches in the NCBI database, and 57 genes encoded capsid, envelope, tegument and nonstructural proteins. Comparative analysis of the genomes of CbBV and a number of representatives of the class nuclear arthropod large DNA viruses (NALDVs) made it possible to isolate 49 evolutionarily conserved orthologue core genes. Among them, 5 were multicopy genes, and 44 were single-copy genes. There were ancestral genes characteristic of all Naldaviricetes - per os infectivity complex genes, one DNA polymerase gene and one thymidylate synthase gene. Phylogenetic analysis of representatives of the Nimaviridae family revealed that the CbBV and Chionoecetes opilio bacilliform virus (CoBV) form an independent clade within the family separate from the clade containing WSSV strains. This is supported by data on the order and arrangement of genes in the genomes of nimaviruses that were identical within each clade but differed between them. In addition, a high identity of the genomes and proteomes of CbBV and CoBV (approximately 99%) was shown, and their identity with WSSV strains was no more than 33%. The data on the structure of the genome of the new virus that causes MHS in C. bairdi indicate that it belongs to the family Nimaviridae, genus Whispovirus. Thus, the CbBV infecting the commercially important species of Tanner crab in populations of the Pacific coast of Kamchatka is the second "wild" representative of replicating nimaviruses whose genome has been characterized after the CoBV that causes MHS in C. opilio in populations of the Sea of Japan. The discovery of a new member of the family that infects decapods indicates the prevalence of nimaviruses in marine ecosystems. The information obtained is important for understanding the evolution of representatives of the class of nuclear arthropod large DNA viruses. The discovery of a new nimavirus that causes MHS in Chionoecetes crabs, in contrast to the white spot syndrome (WSS) caused by WSSV strains, makes it relevant to identify two variants and possibly species within the family, namely, WSSV and Milky Hemolymph Syndrome virus (MHSV).

VP19 is important for the envelope coating of white spot syndrome virus

VP19 is a major envelope protein of white spot syndrome virus (WSSV), an important pathogen of farmed shrimp. However, the exact function of VP19 in WSSV assembly and infection is unknown. To understand the function of VP19, the gene was knocked down by RNA interference. We found that the dsRNA specific for vp19 gene dramatically reduced the replication of WSSV genomic DNA in infected animals. Further investigation by transmission electron microscopy showed that inhibition of VP19 prevented envelope coating of progeny virions, resulting in a high amount of immature virus particles without outer layer (envelope) in the host cells. This finding was further confirmed by SDS-PAGE analysis, which showed the loss of VP19 and other envelope proteins from the improperly assembled virions. These results suggest that VP19 is essential for WSSV envelope coating.

A cuticle protein from the Pacific white shrimp Litopenaeus vannamei involved in WSSV infection

White spot syndrome virus (WSSV) is a major viral pathogen in global shrimp farming, causing huge economic damage. Through penetrating the outer surface of the target tissues, WSSV enters into the cells of the target tissue to complete the replication process in the host. In the present study, a cuticle protein gene from Litopenaeus vannamei, designated as LvAMP13.4, was identified and proved to be involved in WSSV invasion. The deduced amino acid sequence of LvAMP13.4 contained a signal peptide and a conserved chitin-binding domain type 4 (ChBD4). This cuticle protein gene was mainly expressed in stomach, gill and epidermis. The expression level of LvAMP13.4 was significantly changed during WSSV infection. Silencing of LvAMP13.4 by dsRNA interference apparently reduced the mortality rate and the WSSV copy number in shrimp upon WSSV infection. Furthermore, yeast two-hybrid system and Co-IP assay were performed to confirm that LvAMP13.4 could interact with the major envelop protein VP24 of WSSV. These data indicated that LvAMP13.4 was involved in the invasion process of WSSV through interaction with VP24. The present results could provide new insights for us in understanding the role of host cuticle proteins during virus invasion.

A VP24-truncated isolate of white spot syndrome virus is inefficient in per os infection

White spot syndrome virus (WSSV) is a major pathogen of penaeid shrimp. Here we identified a new WSSV strain, WSSV-CN04, from naturally infected Marsupenaeus japonicus. Whole genomic sequencing results indicate that the WSSV-CN04 genome was 281 054 bp in length, and encoded 157 hypothetic proteins. The genome sequence of WSSV-CN04 was most closely related to the low-virulent strain WSSV-CN03, sharing 97.5% sequence identity. Notably, in WSSV-CN04, the major envelop protein VP24 was not only truncated but also absent in the virions. Since VP24 was previously reported to be essential for WSSV per os infection by mediating WSSV-chitin interaction, we further analyzed the peroral infection of WSSV-CN03 and -CN04 in Litopenaeus vannamei, and show that the infectivity of WSSV-CN04 was significantly lower than that of WSSV-CN03. When compared with WSSV-CN03-infected shrimp, fewer virions were detected in the digestive tract tissues of WSSV-CN04-infected shrimp at 4 hours post-infection (hpi), and the viral titers in the animals at 24 hpi were much lower. Moreover, a peptide corresponding to VP24 chitin-binding domain reduced the amount of WSSV-CN03 in the midgut to a level similar to that of WSSV-CN04 at 4 hpi. These findings indicate that the truncation of VP24 may attenuate the peroral infectivity of WSSV-CN04, and therefore verify the important role of VP24 in WSSV per os infection.

Crystal Structure of Major Envelope Protein VP24 from White Spot Syndrome Virus

White spot syndrome virus (WSSV) is one of the major and most serious pathogen in the shrimp industry. As one of the most abundant envelope protein, VP24 acts as a core protein interacting with other structure proteins and plays an important role in virus assembly and infection. Here, we have presented the crystal structure of VP24 from WSSV. In the structure, VP24 consists of a nine-stranded β–barrel fold with mostly antiparallel β-strands, and the loops extending out the β–barrel at both N-terminus and C-terminus, which is distinct to those of the other two major envelope proteins VP28 and VP26. Structural comparison of VP24 with VP26 and VP28 reveals opposite electrostatic surface potential properties of them. These structural differences could provide insight into their differential functional mechanisms and roles for virus assembly and infection. Moreover, the structure reveals a trimeric assembly, suggesting a likely natural conformation of VP24 in viral envelope. Therefore, in addition to confirming the evolutionary relationship among the three abundant envelope proteins of WSSV, our structural studies also facilitate a better understanding of the molecular mechanism underlying special roles of VP24 in WSSV assembly and infection.

VP24 Is a Chitin-Binding Protein Involved in White Spot Syndrome Virus Infection

Oral ingestion is the major route of infection for the white spot syndrome virus (WSSV). However, the mechanism by which virus particles in the digestive tract invade host cells is unknown. In the present study, we demonstrate that WSSV virions can bind to chitin through one of the major envelope proteins (VP24). Mutagenesis analysis indicated that amino acids (aa) 186 to 200 in the C terminus of VP24 were required for chitin binding. Moreover, the P-VP24186-200 peptide derived from the VP24 chitin binding region significantly inhibited the VP24-chitin interaction and the WSSV-chitin interaction, implying that VP24 participates in WSSV binding to chitin. Oral inoculation experiments showed that P-VP24186-200 treatment reduced the number of virus particles remaining in the digestive tract during the early stage of infection and greatly hindered WSSV proliferation in shrimp. These data indicate that binding of WSSV to chitin through the viral envelope protein VP24 is essential for WSSV per os infection and provide new ideas for preventing WSSV infection in shrimp farms.

IMPORTANCE

In this study, we show that WSSV can bind to chitin through the envelope protein VP24. The chitin-binding domain of VP24 maps to amino acids 186 to 200 in the C terminus. Binding of WSSV to chitin through the viral envelope protein VP24 is essential for WSSV per os infection. These findings not only extend our knowledge of WSSV infection but also provide new insights into strategies to prevent WSSV infection in shrimp farms.

Identification of the interaction domains of white spot syndrome virus envelope proteins VP28 and VP24

VP28 and VP24 are two major envelope proteins of white spot syndrome virus (WSSV). The direct interaction between VP28 and VP24 has been described in previous studies. In this study, we confirmed this interaction and mapped the interaction domains of VP28 and VP24 by constructing a series of deletion mutants. By co-immunoprecipitation, two VP28-binding domains of VP24 were located at amino acid residues 46-61 and 148-160, while VP24-binding domain of VP28 was located at amino acid residues 31-45. These binding domains were further corroborated by peptide blocking assay, in which synthetic peptides spanning the binding domains were able to inhibit VP28-VP24 interaction, whereas same-size control peptides from non-binging regions did not.

Characterization of white spot syndrome virus VP52B and its interaction with VP26

White spot syndrome virus (WSSV) is one of the major pathogens of cultured shrimp. Identification of envelope protein interactions has become a central issue for the understanding of WSSV assembly. In this paper, WSSV envelope protein VP52B was fused with GST-tag and expressed in Escherichia coli BL-21(DE3). Immunogold-electron microscopy revealed that VP52B was located on the outside surface of WSSV virions. Far-Western blotting analysis suggested that VP52B might directly interact with a major viral envelope protein VP26, and their interaction was confirmed by GST pull-down assay. Further investigation showed that the VP52B binding domain was located between residues 135-170 of VP26. These findings will enhance our understanding of the molecular mechanisms of WSSV morphogenesis.

Construction and application of a protein interaction map for white spot syndrome virus (WSSV)

White spot syndrome virus (WSSV) is currently the most serious global threat for cultured shrimp production. Although its large, double-stranded DNA genome has been completely characterized, most putative protein functions remain obscure. To provide more informative knowledge about this virus, a proteomic-scale network of WSSV-WSSV protein interactions was carried out using a comprehensive yeast two-hybrid analysis. An array of yeast transformants containing each WSSV open reading frame fused with GAL4 DNA binding domain and GAL4 activation domain was constructed yielding 187 bait and 182 prey constructs, respectively. On screening of ∼28,000 pairwise combinations, 710 interactions were obtained from 143 baits. An independent coimmunoprecipitation assay (co-IP) was performed to validate the selected protein interaction pairs identified from the yeast two-hybrid approach. The program Cytoscape was employed to create a WSSV protein-protein interaction (PPI) network. The topology of the WSSV PPI network was based on the Barabási-Albert model and consisted of a scale-free network that resembled other established viral protein interaction networks. Using the RNA interference approach, knocking down either of two candidate hub proteins gave shrimp more protection against WSSV than knocking down a nonhub gene. The WSSV protein interaction map established in this study provides novel guidance for further studies on shrimp viral pathogenesis, host-viral protein interaction and potential targets for therapeutic and preventative antiviral strategies in shrimp aquaculture.

Low-abundance envelope protein VP12 of white spot syndrome virus interacts with envelope protein VP150 and capsid protein VP51

VP12 and VP150 are two minor envelope proteins of white spot syndrome virus (WSSV). In our previous studies, VP12 was found to co-migrate with 53-kDa form of VP150 on two-dimensional Blue Native/SDS-PAGE, suggesting that there is an interaction between them. In this study, we confirmed the interaction by co-immunoprecipitation assay and demonstrated that the binding region with VP12 is located between residues 207 and 803 of VP150. Further studies found that VP12 can be attached to WSSV capsids by interacting with capsid protein VP51. These findings suggest that VP12 may function as a linker protein participating in the linkage between VP12/VP150 complex and viral nucleocapsid.

Role of chymotrypsin-like serine proteinase in white spot syndrome virus infection in Fenneropenaeus chinensis

White spot syndrome virus (WSSV) caused a great economic loss in shrimp aquaculture. Although great efforts have been undertaken to characterize the virus disease during the last two decades, there are still lack of effective methods to prevent or cure it. In this study, we investigated the transcriptional expression profiles of 18 key immune-related genes in the Chinese shrimp Fenneropenaeus chinensis which was severely infected by WSSV. We found that the expression levels of 6 genes including chymotrypsin-like serine proteinase (CH-SPase), heat shock protein 70 cognate (HSP70), penaeidin (PEN), peroxinectin (PO), proliferating cell nuclear antigen (PCNA) and argonaute (AGO) changed significantly, while the expression of the other 12 genes had no significant changes compared to the control group. Among the 6 screened genes, CH-SPase showed significantly up-regulation, while the other 5 ones were significantly down-regulated. Knockdown of the expression of CH-SPase in WSSV-infected Chinese shrimp reduced the copy number of WSSV and delayed cumulative mortalities, suggesting that CH-SPase is important for WSSV infection. This study will be helpful to control the disease in shrimp caused by WSSV.

Proteomics and its applications to aquaculture in China: infection, immunity, and interaction of aquaculture hosts with pathogens

China is the largest fishery producer worldwide in term of its aquaculture output, and plays leading and decisive roles in international aquaculture development. To improve aquaculture output further and promote aquaculture business development, infectious diseases and immunity of fishes and other aquaculture species must be studied. In this regard, aquaculture proteomics has been widely carried out in China to get a better understanding of aquaculture host immunity and microbial pathogenesis as well as host-pathogen interactions, and to identify novel disease targets and vaccine candidates for therapeutic interventions. These proteomics studies include development of novel methods, assays, and advanced concepts in order to characterize proteomics mechanisms of host innate immune defense and microbial pathogenesis. This review article summarizes some recently published technical approaches and their applications to aquaculture proteomics with an emphasis on the responses of aquaculture animals to bacteria, viruses, and other aqua-environmental stresses, and development of broadly cross-protective vaccine candidates. The reviewed articles are those that have been published in international peer reviewed journals.

Comparative efficacy of double-stranded RNAs targeting WSSV structural and nonstructural genes in controlling viral multiplication in Penaeus monodon

RNA interference (RNAi) is a potential strategy to control shrimp viral diseases, including the white spot disease caused by White Spot Syndrome Virus (WSSV). Selection of genes for targeting is an important criterion. We have compared the efficacy of dsRNAs targeting structural (vp28 and vp281) and nonstructural genes (rr1 and dnapol) of WSSV in controlling viral multiplication in Penaeus monodon. Targeting the rr1 and vp28 genes provided better protection (93.3% and 90% survival respectively) compared to vp281 and dnapol in experimentally infected shrimp. Temporal transcriptional analysis of the corresponding genes and PCR-based diagnosis of WSSV in samples collected at different time points in the experiment supported this observation, thereby indicating that targeting a combination of rr1 and vp28 would be effective in limiting WSSV multiplication.