Blotched Snakehead Virus Is a New Aquatic Birnavirus That Is Slightly More Related to Avibirnavirus Than to Aquabirnavirus

Abstract

By different approaches, we characterized the birnavirus blotched snakehead virus (BSNV).The family Birnaviridae includes three genera: Aquabirnavirus with the infectious pancreatic necrosis virus (IPNV) species, Avibirnavirus with the infectious bursal disease virus (IBDV) species, and Entomobirnavirus with the Drosophila X virus (DXV) species. Birnavirus particles are single-shelled unenveloped viruses with Tϭ13 icosahedral capsids and are about 60 nm in diameter. VP2 and VP3 form the outer and inner layers, respectively, of the virions, which contain several VP1 molecules and the bisegmented double-stranded RNA genome (5,13,14,27). Both genomic segments A and B of DXV and of a large number of IPNV and IBDV strains have been cloned and sequenced (1, 3, 4, 6, 7, 9-11, 15-17, 19, 21, 22, 24, 28-31, 34-36). Segment B codes for a putative RNAdependent RNA polymerase, VP1. Segment A contains two overlapping reading frames (ORFs). In IPNV and IBDV, the smallest ORF is 5Ј proximal and encodes VP5, a nonstructural polypeptide, whereas for DXV, the small ORF resides in the 3Ј-half of the segment. The large ORF encodes a 110-kDa polyprotein (NH 2 -pVP2-VP4-VP3-COOH). The polyprotein is cotranslationally processed through the proteolytic activity of VP4 to generate pVP2, VP4, and VP3. Cleavage sites at pVP2-VP4 and VP4-VP3 junctions have been identified for IPNV, IBDV, and DXV (11,26,32,33). For IBDV, the processing of pVP2 (amino acids [aa] 1 to 512) generates VP2 and four small peptides (aa 442 to 487 [M. Skinner, personal communication], 488 to 494, 495 to 501, and 502 to 512) (12). At least three of these peptides (aa 442 to 487, 488 to 494, and 502 to 512) are associated with the viral particles (12). This maturation cleavage process of pVP2 requires assembly of viral capsids (8). The IBDV and IPNV VP4 proteases have been shown to use a serine-lysine catalytic dyad to control the processing of the polyprotein (2, 26, 32).The blotched snakehead virus (BSNV) was isolated from a cell line derived from the blotched snakehead fish (Channa lucius). Although BSNV has been proposed to belong to the family Birnaviridae on the basis of biochemical characteristics, cross-neutralization assays have established the serological distinctness of BSNV from IPNV (20). In this study, we further characterized BSNV.Molecular cloning and sequence of the BSNV genomic segments A and B. The BSNV used in this study (kindly provided by W. Starkey, Stirling University, Stirling, United Kingdom) was propagated onto a cell line derived from Ophicephalus striatus by W. Wattanavijarn (Veterinary Faculty, Chulalongkorn University, Bangkok, Thailand) and provided by P. de Kinkelin (Institut National de la Recherche Agronomique, Jouy-en-Josas, France). Once the cytopathic effect was complete, virus was purified by CsCl gradient centrifugation as previously described (12). The viral RNA was extracted following sodium dodecyl sulfate (SDS)-proteinase K treatment and recovered following phenol-chloroform extraction and ethanol precipitation. For the fi...

Phylogenetic evidence for homologous recombination within the family Birnaviridae

“…The genome segment A of birnaviruses (~3 kb) mainly encodes a pVP2-4-3 polyprotein and the genome segment B (~2.8 kb) encodes an RNA-dependent RNA polymerase (RdRp) named VP1 (Delmas et al, 2005). Homologous proteins of birnaviruses share only~20 to 50 % amino acid identity (Da Costa et al, 2003;Nobiron et al, 2008). Intraspecies diversity of IBDV and AQBV has been characterized extensively, while the diversity of DXV, BSNV and TV-1 is currently unknown.…”

Crystal Structure of a Viral Protease Intramolecular Acyl-enzyme Complex

“…In segment A, the largest open reading frame encodes a polyprotein that has the conserved arrangement of NH 2 -pVP2-VP4-VP3-COOH with the exception of gene X, which exists between pVP2 and VP4 in TV-1 ( Fig. 1) and Blotched snakehead virus (BSNV) (6,7). The polyprotein is processed by the self-encoded protease viral protein 4 (VP4) to generate the capsid precursor protein pVP2, VP4 itself, and ribonucleoprotein VP3 (6, 8 -10).…”

Crystal Structure of an Aquabirnavirus Particle: Insights into Antigenic Diversity and Virulence Determinism

“…Aquatic birnaviruses are the most abundant and diverse and are grouped in two separate genera: the Aquabirnavirus genus and the Blosnavirus genus, with infectious pancreatic necrosis virus (IPNV) and blotched snakehead virus (BSNV) (16) as respective type species. A third aquatic birnavirus of unassigned genus, Tellina virus 1, was recently described and found to be phylogenetically distant from the two established genera (40).…”