Characterization of the endonuclease activity of the replication-associated protein of beak and feather disease virus.

Beak and feather disease virus (BFDV) belongs to the family Circoviridae. A rolling-circle replication strategy based on a replication-associated protein (Rep) has been proposed for BFDV. The Rep gene of BFDV was expressed and purified, and it was shown to cleave short oligonucleotides containing the conserved nonanucleotide sequence found in the replication origin of circoviruses. This endonuclease activity was most efficient in the presence of the divalent metal ions Mg2+ and Mn2+. Rep proteins containing mutation in the ATPase/GTPase motifs and the 14FTLNN18, 61KKRLS65, 89YCSK92, and 170GKS172 motifs lacked endonuclease activity. The endonuclease activity was not affected by ATPase inhibitors, with the exception of N-ethylmaleimide (NEM), or by GTPase inhibitors, but it was decreased by treatment with the endonuclease inhibitor L-742001. Both the ATPase and GTPase activities were decreased by site-directed mutagenesis and deletion of the ATPase/GTPase and endonuclease motifs. The Rep protein was able to bind a double-stranded DNA fragment of P36 (dsP36) containing the stem-loop structure of the replication origin of BFDV. All of the Rep mutant proteins showed reduced ability to bind this fragment, suggesting that all the ATPase/GTPase and endonuclease motifs are involved in the binding. Other than NEM, all ATPase, GTPase, and endonuclease inhibitors inhibited the binding of the Rep protein to the dsP36 fragment. This is the first report describing the endonuclease activity of the Rep protein of BFDV.

Development of an antigen-capture ELISA for beak and feather disease virus.

Psittacine beak and feather disease (PBFD) is characterised by degenerative feather, feather dystrophy, and beak deformity. Sometimes acute forms can lead to fatal cases in nestlings. The worldwide distribution of this disease affects numerous species of parrots with an average prevalence of 40%, including in Taiwan. The pathogen of PBFD is beak and feather disease virus (BFDV), which is a single-stranded circular DNA virus, circovirus. To date, hemagglutination and PCR assays have been routinely used to detect this virus. In this study, both the replication-associated protein (Rep) and the structural capsid protein (Cap) were expressed and then used as antigens for the production of monoclonal antibodies. Conserved epitopes recognised by the anti-Cap and anti-Rep monoclonal antibodies were determined to be NFEDYRI and LSALKKM, respectively. Clinical samples collected from different species of parrots were tested by hemagglutination, PCR, and anti-Cap antigen-capture ELISA assays and the positive rates were the same at 49%. Thus, this anti-Cap antigen-capture ELISA is able to be used for the rapid identification of BFDV-infected birds in a non-invasive manner.