Functional analysis of duck, goose, and ostrich 2′-5′-oligoadenylate synthetase

Up-to-date the flavivirus infection in avian taxa is not clearly defined. Several reports have demonstrated that many viruses belonging to Flaviviridae may cause diseases in poultry species; however, the susceptibility of other avian species is variable and still unclear. In human and mice, the 2'-5'-oligoadenylate synthetase (OAS) proteins are associated with resistance to the flavivirus infection as well as other virus infections. However, the avian OAS proteins are rarely studied. In our previous studies, we confirmed that the chicken OAS-like protein (chOASL) expressed OAS-enzymatic activity (the classical OAS/RNase L-dependent pathway) as well as the anti-flavivirus activity (the putative OAS/RNase L-independent pathway). Therefore, the current study aimed at functional analysis of avian OAS proteins from duck, goose, and ostrich. The duOASL, goOASL, and osOAS1 proteins expressed enzymatic activity as well as chOASL, whereas osOASL expressed little enzymatic activity. On the other hand, duOASL, goOASL, and osOASL possessed significant antiviral activity against West Nile virus (WNV)-replicon replication as well as chOASL, whereas osOAS1 did not. In addition, similar to chOASL, their antiviral activity was independent of RNase L activation. These results suggest that OASL is the only OAS protein in the duck and goose as well as chicken and possesses both OAS-enzymatic and anti-flavivirus activities, whereas the ostrich possesses both OAS1 and OASL proteins with sharing the functional activities, OAS-enzymatic and anti-flavivirus activities, respectively. It is of interest that the ostrich undergoes differential process in OAS gene evolution from other poultries and thus possesses different molecular mechanism in antiviral activity.