Characterization of the genes encoding two of the major capsid proteins of epizootic haemorrhagic disease virus indicates a close genetic relationship to bluetongue virus

Abstract

The sequences of the genes of two of the major capsid proteins of epizootic haemorrhagic disease virus serotype 1 (EHDV-1, Orbivirus genus, Reoviridae) have been determined by analyses of cDNA clones representing the L2 and $7 RNA segments. The EHDV-1 $7 RNA segment, which encodes the VP7 core protein, is 1162 nucleotides in length and has the capacity to encode 349 amino acids (Mr 38243). The EHDV-1 L2 RNA segment, which encodes the outer capsid VP2 protein (Mr 113 249) is 2968 nucleotides in length and has an open reading frame of 971 codons. The potential secondary structure of the EHDV-1 $7 mRNA species, in particular that of the terminal regions, is comparable to those of the corresponding segments of bluetongue virus (BTV) and African horse sickness virus (AHSV); the EHDV-1 L2 mRNA species has a secondary structure similar to that of the L2 mRNA of BTV. The EHDV-1 VP2 and VP7 proteins, as well as those of the other two major structural proteins of EHDV published previously (the inner core VP3 protein and the second outer capsid, VP5), are closely related to the corresponding proteins of BTV. The EHDV and BTV VP7 sequences are more distantly related to the sequence of the AHSV VP7 protein published recently.

Detection of a novel reassortant epizootic hemorrhagic disease virus (EHDV) in the USA containing RNA segments derived from both exotic (EHDV-6) and endemic (EHDV-2) serotypes

“…The fact that VP2 and VP5 must interact directly with one other (albeit not extensively) to form the outer capsid, as demonstrated in the closely related BTV (Nason et al, 2004), and that VP2 (Fig. 1b) and to a lesser extent VP5 are more variable in amino acid sequence than other EHDV proteins (Iwata et al, 1991(Iwata et al, , 1992, may impart some degree of functional and/or conformational constraints that inhibit the survival of reassortants bearing outer surface proteins derived from two different EHDV serotypes. Additionally, reassortants containing chimeric outer capsid proteins have been shown to be difficult to produce and isolate in vitro, suggesting that reassortants containing VP2 and VP5 derived from contrasting serotypes may be exceedingly rare in nature (Mertens, 1999).…”

“…Based on genetic comparisons with a bovine EHDV-6 isolate from South Africa (M44/96), in conjunction with virus neutralization testing with exotic EHDV antisera, the L2 RNA segment (encoding the VP2 gene predominantly responsible for serotype specificity and mammalian receptor binding/cell entry) of the 2006 isolates was derived from EHDV-6 (Iwata et al, 1992;Hassan & Roy, 1999). Further genetic comparisons of the VP2 gene of all 12 isolates recovered from 2006-2008 indicated that they all share the same L2 RNA segment and are probably derived from the same reassortment event.…”

Major core protein VP7 of Australian bluetongue virus serotype 15: sequence and antigenicity divergence from other BTV serotypes

“…(iv) The most highly conserved domain in all BTV VP7 molecules, including BTV-15 VP7, was located at the N terminus between residues 28 and 54. This region seems to be highly conserved in VP7 from other Culicoides-borne but not tick-borne orbiviruses (Roy et al, 1991;Iwata et al, 1992;Moss et al, 1992). Recent studies have revealed that although core particles of BTV show a large reduction in their infectivity for vertebrate cells compared with intact viruses, they remain infectious to insect cells to the same degree as complete virus particles (Mellor, 1990).…”

Production of a Recombinant Major Inner Capsid Protein for Serological Detection of Epizootic Hemorrhagic Disease Virus

“…All EHDV serotypes share an antigen which enables their identification and differentiation from other orbiviruses, such as bluetongue virus (BTV) (4,20). This group-specific antigen is specified by a protein (VP7) located on the inner coat of the virus particle, making it a suitable antigen for use in serological assays to specifically identify EHDV regardless of the serotype (16,17).…”