A virulent isolate of yellow head nidovirus contains a deformed envelope glycoprotein gp116

Abstract

Yellow head virus (YHV) is a highly virulent pathogen of penaeid shrimp. An isolate obtained from Penaeus vannamei during a yellow head disease outbreak in February 2006 in Ratchaburi Province, Thailand was purified following passage in experimentally infected shrimp. SDS-PAGE of purified virions indicated that envelope glycoprotein gp116 in the Ratchaburi/2006 isolate was smaller and relatively less abundant than in the Chachoengsao/1998 YHV reference strain. The variant gp116 reacted poorly in immunoblots with a gp116 mouse monoclonal antibody and a rabbit anti-serum to a baculovirus-expressed, C-terminally truncated, [His](6)-tagged gp116 that reacted strongly with gp116 of the homologous Chachoengsao/1998 strain. The anti-gp116 polyclonal serum also failed to neutralise the infectivity of the Ratchaburi/2006 isolate in in-vivo assays conducted in P. vannamei, but effectively neutralised the infectivity of the reference strain. Sequence analysis of the approximately 6.0 kb structural protein gene region and 3'UTR of the Ratchaburi/2006 isolate indicated >99.9% overall nucleotide identity with the Chachoengsao/1998 strain. However, in Ratchaburi/2006 a deletion in ORF3, corresponding to 54 amino acids near the N-terminal signal peptidase cleavage site of gp116, resulted in the loss of six conserved cysteine residues and two predicted N-glycosylation sites. Analysis of this ORF3 region in 25 viruses representing each of the six genotypes in the yellow head complex identified this modified form of gp116 in two other virulent YHV isolates classified as genotype 1b. The data indicate that, although the deletion causes a significant structural deformation of gp116 which reduces its incorporation into virions and eliminates the major neutralisation sites, the virus remains highly infectious, virulent and fit for survival.

Glycosylation of gp116 and gp64 envelope proteins of yellow head virus of Penaeus monodon shrimp

“…Most sequence diversity, including block insertions/deletions, occurs near to the gp116 N terminus, generated by cleavage at a signal peptidase type 1 site at TM domain 3 of the ORF3 polyprotein. Two YHV genotype 1 variants from Thailand, one virulent (genotype 1b) (Sittidilokratna et al, 2009) and the other non-virulent (A-YHV) (Gangnonngiw et al, 2009), for which sequence data have been reported recently, both possess a 54 aa deletion in the gp116 Nterminal region that eliminates the N 63 TS and N 44 ST sites, found here to be glycosylated in the YHV genotype 1a strain. Despite sequence differences and the loss of these two glycan-linked sites in gp116 of YHV genotype 1b strains, they retain virulence, albeit somewhat reduced compared with genotype 1a strains (Sittidilokratna et al, 2009).…”

“…Two YHV genotype 1 variants from Thailand, one virulent (genotype 1b) (Sittidilokratna et al, 2009) and the other non-virulent (A-YHV) (Gangnonngiw et al, 2009), for which sequence data have been reported recently, both possess a 54 aa deletion in the gp116 Nterminal region that eliminates the N 63 TS and N 44 ST sites, found here to be glycosylated in the YHV genotype 1a strain. Despite sequence differences and the loss of these two glycan-linked sites in gp116 of YHV genotype 1b strains, they retain virulence, albeit somewhat reduced compared with genotype 1a strains (Sittidilokratna et al, 2009). It has been postulated that sequence differences elsewhere, possibly in non-structural proteins, are important in conferring virulence of these two variants of YHV genotype 1 (Gangnonngiw et al, 2009).…”

“…Of the three YHV structural proteins, the amino acid sequence of gp116 is most variable amongst the genotypic variants (Gangnonngiw et al, 2009;Sittidilokratna et al, 2009;Wijegoonawardane et al, 2008). Most sequence diversity, including block insertions/deletions, occurs near to the gp116 N terminus, generated by cleavage at a signal peptidase type 1 site at TM domain 3 of the ORF3 polyprotein.…”

Pathogenicity of gill-associated virus and Mourilyan virus during mixed infections of black tiger shrimp (Penaeus monodon)

“…2). However, as reported previously, GAV is far less virulent than YHV for which the LD 50 is typically 10 8 -to 10 9 -fold lower in inocula containing equivalent viral genetic loads (Sittidilokratna et al, 2009a;Wijegoonawardane et al, 2009). Consequently, YHV lethal challenge experiments in which very effective RNAiinduced inhibition of infection was observed employed a virus dose~10 5 -fold lower than was possible for GAV (Yodmuang et al, 2006).…”

New yellow head virus genotype (YHV7) in giant tiger shrimp Penaeus monodon indigenous to northern Australia

“…YHV3 in Thailand and Vietnam, YHV4 in India, YHV5 in Malaysia, Thailand and the Philippines, and YHV6 in Mozambique). YHV1 types occurring in Thailand have also been assigned to subtypes YHV1a and YHV1b based on the latter possessing a 54 amino acid deletion in the N-terminal region of the ORF3 coding sequence, although both genotypes retain similar virulence in P. vannamei (Sittidilokratna et al 2009, Senapin et al 2010.…”