The banana streak virus (BSV) capsid protein contains an N-terminal, intrinsically disordered (NID) domain that is surface-exposed on the virion and likely is multifunctional and plays important roles in viral replication and transmission. The immunodominant continuous epitopes on the virion are also located in the NID domain, and therefore this domain is of great interest from a diagnostics perspective. The BSV capsid protein is cleaved from a larger polyprotein through the action of the virus-encoded aspartic protease but the enzyme substrate sites, and hence the protein boundaries, have not yet been determined. Success has been achieved in expressing the cauliflower mosaic virus (CaMV) aspartic protease in E. coli using methods developed for mammalian-infecting retroviruses and enzyme activity is currently being investigated. Once methods are optimized for CaMV, then work will begin on characterizing the BSV AP.
Using chemically synthesized peptides to mimic the continuous epitopes in the BSV NID domain, antisera have been raised in rabbits, and shown to cross-react with the virus in a range of assay formats such as ELISA, immunosorbent electron microscopy and immunocapture PCR. This technology promises to provide a rapid and reproducible way of generating immunodiagnostic reagents for all plant-infecting pararetroviruses.