Triatovirus: A new genus in the family Dicistroviridae

ECHEVERRÍA M. G; SUSEVICH, M. L; METZ, G.E; MARTI G. A; BALSALOBRE, A

ARCHIVES OF VIROLOGY

SPRINGER WIEN

Lugar: Viena; Año: 2016 p. 1 - 7

0304-8608

Triatoma virus (TrV) differs substantially in surface features from Cricket paralysis virus (CrPV), in the absence of an ordered VP4 molecule in the capsid interior and in the presence in VP3 of a structurally conserved catalytic motif involving the same DDF sequence as in VP1.The two main differences between the TrV and CrPV capsids are the projections at the TrV surface, which are absent in CrPV. These projections are made from an inserted sequence element, and the presence of the same insertion in other members of the proposed genus (Plautia stali intestine virus ?PSIV-, Himetobi P virus ?HiPV-, and Black queen cell virus -BQCV-) suggest that they are also likely to have the same structural features (Agirre et al., 2011, Squirres et al., 2013). The structure suggests that the exposed residues in these projections are likely to play a role in the interactions with the host; for instance, an entry receptor.The second difference is the presence of a DDF motif in the homologous location in VP3, where it is also exposed to the capsid interior, whereas in CrPV, Aphid lethal paralysis virus ?ALPV-, Drosophila C virus -DCV- and Rhopalosiphum padi virus ?RhPV-, this motif is only found in VP1, where it is believed to account for cleavage of the VP0 precursor. This difference may account for additional proteolysis in VP1 during RNA release. Intriguingly, a second DDF motif (3254?3256) is present in VP3 at the same location in the structure at the corner between the BIDG sheet and the βx1βx2 sheet, which is equivalent to the βx3βx4 sheet in VP1. This motif is also conserved in BQCV, HiPV, PSIV and TrV but is not found in CrPV or in DCV, APLV or RhPV, which is the closest neighbour to CrPV in the current Dicistroviridae phylogenetic tree. Finally, the most striking difference is the absence of ordered VP4. The fact that this protein is not part of the ordered capsid in fully infectious TrV virions is in sharp contrast to what occurs with the same protein in CrPV, where it is found to be well structured around the fivefold axis. Such differences preclude assignment of a general function to VP4 in the Dicistroviridae family, and this also remains to be further elucidated (Squires et al, 2013).Sequence alignmentTaking into account that in the phylogenetic tree of the dicistrovirus family TrV belongs to a different branch from that of ABPV and CrPV (Bonning and Miller, 2010), as well as the biological, genetic, and structural knowledge regarding this virus, it is reasonable to propose TrV as the reference for a third Dicistroviridae family genus named Triatovirus (Agirre et al., 2011).Phylogenetic analysis of deduced amino-acid sequences of the three major coat proteins (ORF 2) from the following dicistroviruses were done. The criterion employed for the selection of the viruses was based on the availability of seqeuences in GenBank. The alignment was performed using the Clustal2 phylogeny. Homalodisca coagulata virus (HocV-1) do not have any DDF motif, but in the phylogenetic tree is nearest the Triatovirus genus proposed. Please see (Figure 1).