Abstract:
African horse sickness is a deadly and highly infectious disease of equids, caused by
African horse sickness virus (AHSV). AHSV is one of the most economically important members of
the Orbivirus genus. AHSV is transmitted by the biting midge, Culicoides, and therefore replicates
in both insect and mammalian cell types. Structural protein VP7 is a highly conserved major core
protein of orbiviruses. Unlike any other orbivirus VP7, AHSV VP7 is highly insoluble and forms flat
hexagonal crystalline particles of unknown function in AHSV-infected cells and when expressed in
mammalian or insect cells. To examine the role of AHSV VP7 in virus replication, a plasmid-based
reverse genetics system was used to generate a recombinant AHSV that does not form crystalline
particles. We characterised the role of VP7 crystalline particle formation in AHSV replication in vitro
and found that soluble VP7 interacted with viral proteins VP2 and NS2 similarly to wild-type
VP7 during infection. Interestingly, soluble VP7 was found to form uncharacteristic tubule-like
structures in infected cells which were confirmed to be as a result of unique VP7-NS1 colocalisation.
Furthermore, it was found that VP7 crystalline particles play a role in AHSV release and yield.
This work provides insight into the role of VP7 aggregation in AHSV cellular pathogenesis and
contributes toward the understanding of the possible effects of viral protein aggregation in other
human virus-borne diseases.
