Identification and phylogeny of a non-specific endonuclease gene of white spot syndrome virus of shrimp

Bacterial non-specific nucleases of the phospholipase D superfamily and their biotechnological potential

Bacterial non-specific nucleases are ubiquitously distributed and involved in numerous intra- and extracellular processes. Although all nucleases share the basic chemistry for the hydrolysis of phosphodiester bonds in nucleic acid molecules, the catalysis comprises diverse modes of action, which offers great potential for versatile biotechnological applications. A major criterium for their differentiation is substrate specificity. Specific endonucleases are widely used as restriction enzymes in molecular biology approaches, whereas the main applications of non-specific nucleases (NSNs) are the removal of nucleic acids from crude extracts in industrial downstream processing and the prevention of cell clumping in microfabricated channels. In nature, the predominant role of NSNs is the acquisition of nutrient sources such as nucleotides and phosphates. The number of extensively characterized NSNs and available structures is limited. Moreover, their applicability is mostly challenged by the presence of metal chelators that impede the hydrolysis of nucleic acids in a metal ion-dependent manner. However, a few metal ion-independent NSNs that tolerate the presence of metal chelators have been characterized in recent years with none being commercially available to date. The classification and biotechnological potential of bacterial NSNs with a special focus on metal ion-independent nucleases are presented and discussed.Key Points • Bacterial phospholipases (PLD-family) exhibit nucleolytic activity. • Bacterial nucleases of the PLD-family are metal ion-independent. • NSNs can be used in downstream processing approaches.

Identification, functional characterization and phylogenetic analysis of double stranded RNA degrading enzymes present in the gut of the desert locust, Schistocerca gregaria

RNA interference (RNAi) has become a widely used reverse genetics tool in eukaryotes and holds great potential to contribute to the development of novel strategies for insect pest control. While previous studies clearly demonstrated that injection of dsRNA into the body cavity of the desert locust, Schistocerca gregaria, is highly effective to induce gene silencing effects, we observed that the RNAi response is much less sensitive to orally delivered dsRNA. In line with this, we report on the presence of a potent dsRNA degrading activity in the midgut juice. Four different dsRNase sequences that belong to the DNA/RNA Non-specific Nuclease superfamily were retrieved from a transcriptome database of the desert locust. Surprisingly, we have found that, in the publicly available eukaryote nucleotide sequence databases, the presence of this group of enzymes is restricted to insects and crustaceans. Nonetheless, phylogenetic analyses predict a common origin of these enzymes with the Endonuclease G (EndoG) Non-specific Nucleases that display a widespread taxonomic distribution. Moreover, in contrast to the Sg-endoG transcript, the four Sg-dsRNase transcripts appear to be specifically expressed in the gut. Finally, by means of RNAi, we provide evidence for an important contribution of dsRNase2 to the dsRNA degrading activity that is present in the gut lumen of S. gregaria.

White spot syndrome virus: an overview on an emergent concern

Viruses are ubiquitous and extremely abundant in the marine environment. One of such marine viruses, the white spot syndrome virus (WSSV), has emerged globally as one of the most prevalent, widespread and lethal for shrimp populations. However, at present there is no treatment available to interfere with the unrestrained occurrence and spread of the disease. The recent progress in molecular biology techniques has made it possible to obtain information on the factors, mechanisms and strategies used by this virus to infect and replicate in susceptible host cells. Yet, further research is still required to fully understand the basic nature of WSSV, its exact life cycle and mode of infection. This information will expand our knowledge and may contribute to developing effective prophylactic or therapeutic measures. This review provides a state-of-the-art overview of the topic, and emphasizes the current progress and future direction for the development of WSSV control strategies.

A review on the morphology, molecular characterization, morphogenesis and pathogenesis of white spot syndrome virus

Since it first appeared in 1992, white spot syndrome virus (WSSV) has become the most threatening infectious agent in shrimp aquaculture. Within a decade, this pathogen has spread to all the main shrimp farming areas and has caused enormous economic losses amounting to more than seven billion US dollars. At present, biosecurity methods used to exclude pathogens in shrimp farms include disinfecting ponds and water, preventing the entrance of animals that may carry infectious agents and stocking ponds with specific pathogen-free post-larvae. The combination of these practices increases biosecurity in shrimp farming facilities and may contribute to reduce the risk of a WSSV outbreak. Although several control methods have shown some efficacy against WSSV under experimental conditions, no therapeutic products or strategies are available to effectively control WSSV in the field. Furthermore, differences in virulence and clinical outcome of WSSV infections have been reported. The sequencing and characterization of different strains of WSSV has begun to determine aspects of its biology, virulence and pathogenesis. Knowledge on these aspects is critical for developing effective control methods. The aim of this review is to present an update of the knowledge generated so far on different aspects of WSSV organization, morphogenesis, pathology and pathogenesis.

Functional identification of the non-specific nuclease from white spot syndrome virus

The product encoded by the wsv191 gene from shrimp white spot syndrome virus (WSSV) is homologous with non-specific nucleases (NSN) of other organisms. To functionally identify the protein, the wsv191 gene was expressed in Escherichia coli as a glutathione S-transferase (GST) fusion protein with 6His-tag at C-terminal. The fusion protein (termed as rWSSV-NSN) was purified using Ni-NTA affinity chromatography under denatured conditions, renatured and characterized by three methods. The results showed that rWSSV-NSN could hydrolyze both DNA and RNA. 5'-RACE result revealed that the transcription initiation site of the wsv191 gene was located at nucleotide residue G of the predicted ATG triplet. Therefore, we concluded that the next ATG should be the genuine translation initiation codon of the wsv191 gene. Western blot analysis revealed that the molecular mass of natural WSSV-NSN was 37 kDa.

Vp28 of shrimp white spot syndrome virus is involved in the attachment and penetration into shrimp cells

White spot disease (WSD) is caused by the white spot syndrome virus (WSSV), which results in devastating losses to the shrimp farming industry around the world. However, the mechanism of virus entry and spread into the shrimp cells is unknown. A binding assay in vitro demonstrated VP28-EGFP (envelope protein VP28 fused with enhanced green fluorescence protein) binding to shrimp cells. This provides direct evidence that VP28-EGFP can bind to shrimp cells at pH 6.0 within 0.5 h. However, the protein was observed to enter the cytoplasm 3 h post-adsorption. Meanwhile, the plaque inhibition test showed that the polyclonal antibody against VP28 (a major envelope protein of WSSV) could neutralize the WSSV and block an infection with the virus. The result of competition ELISA further confirmed that the envelope protein VP28 could compete with WSSV to bind to shrimp cells. Overall, VP28 of the WSSV can bind to shrimp cells as an attachment protein, and can help the virus enter the cytoplasm.

A novel envelope protein involved in White spot syndrome virus infection

One open reading frame (designated vp76) from the White spot syndrome virus (WSSV) genome has the motif of a cytokine I receptor and has been identified as a structural protein. In this paper, vp76 was expressed in Escherichia coli and used to prepare a specific antibody to determine the location of the corresponding protein in the intact virion, the nucleocapsids and the envelope of WSSV. Western blotting with the VP76 antiserum confirmed that VP76 was an envelope protein of WSSV. To investigate the function of the VP76, WSSV was neutralized with the VP76-specific antiserum at different concentrations and injected intramuscularly into crayfish. The mortality curves showed that the VP76 antiserum could partially attenuate infection with WSSV, suggesting that VP76 is an envelope protein involved in WSSV infection.

Characterization of ORF89--a latency-related gene of white spot syndrome virus

Open reading frame 89 (ORF89) is one of the three genes that are believed to be involved in the latent infection of white spot syndrome virus (WSSV). Here, we report the structure and functional characterization of ORF89. cDNA sequencing, 5' RLM-RACE, and 3' RLM-RACE showed that ORF89 gene is transcribed into an unspliced mRNA of 4436 nucleotides, which is predicted to encode a protein of 1437 amino acids. ORF89 expressed an approximately 165-kDa protein in Sf9 cells that localized in the nucleus. Amino acids 678-683 were found to be essential for nuclear localization. Cotransfection assays demonstrated that ORF89 protein repressed its own promoter as well as those of a protein kinase and the thymidine-thymidylate kinase genes of WSSV. SYBR Green real-time PCR indicated that the repression occurred at the transcriptional level.

A phage-displayed peptide can inhibit infection by white spot syndrome virus of shrimp

White spot disease, caused by white spot syndrome virus (WSSV), results in devastating losses to the shrimp farming industry around the world, and no effective treatments have been found. Control focuses on exclusion of the virus from culture ponds but, once introduced, spread is often rapid and uncontrollable. The purpose of this study was to select a phage-displayed peptide that might be able to prevent WSSV infection. A 10-mer phage display peptide library (titre 7.2 x 10(7)) was constructed and screened against immobilized WSSV. Selected peptides were assessed for specificity and efficiency of inhibition of virus infection. Of four peptides that specifically bound to WSSV one, designated 2E6, had a high specificity and blocked virus infection, with the possible critical motif for virus inhibition being VAVNNSY. The results suggest that peptide 2E6 has potential for exploitation as an antiviral peptide drug.

Genomic instability of prawn white spot bacilliform virus (WSBV) and its association to virus virulence

Prawn White Spot Bacilliform Virus (WSBV) is a major pathogen that causes prawn diseases. In this study, we examined the sequence of WSBV genome DNA in the shrimp Penaeus japonicus, P. vannamei, P. Monodon, P. chinensis and Metapenaeus ensis through successive PCR amplification of the DNA fragments in the whole WSBV genome. We found a sequence deletion hotspot in the WSBV genome that is 305107 bp in length. The sizes of the deleted fragments were 4.6, 4.8 or 8.1 kbp depending on the species of prawn. Since the mortality of shrimp infected by the intact WSBV was always significantly higher than that of shrimp infected by DNA fragment-deleted WSBV, we suggest that this deletion be somehow linked to the virulence of the virus itself. This result may lead to the discovery of the molecular mechanism of the pathogenicity of WSBV in shrimps.