Analysis of the Relationship Between Enzymatic and Antiviral Activities of the Chicken Oligoadenylate Synthetase-Like

The oligoadenylate synthetase (OAS) is well known as an antiviral factor against the flavivirus infection in mammals. It is known that the oligoadenylate synthetase-like (ChOAS-L) gene is only present in the chicken genome. It has been shown in the previous report that the ChOAS-L possesses enzymatic activity to convert ATP into 2'-5'-linked oligoadenylates and antiviral activity against West Nile virus (WNV) replicon. Therefore, this study aimed to investigate the relationship between enzymatic and antiviral activities of ChOAS-L. Eight mutated ChOAS-L proteins were generated using either the site-directed mutagenesis or standard polymerase chain reaction protocol. The wild-type and mutated proteins were ectopically expressed in 293FT cells to analyze the enzymatic activity and in BHK-21 and BALB/3T3 cells to analyze the antiviral activity using WNV replicon. The results revealed that all mutated proteins showed no enzymatic activity except for ChOAS-L-A Delta UbL2. However, all mutated proteins showed antiviral activity to inhibit the replication of the WNV replicon except for ChOAS-L-A Delta UbL1/UbL2, which showed a partial inhibition compared to the wild-type ChOAS-L-A or other mutated proteins. These results suggest that the ChOAS-L expresses the antiflavivirus activity in a manner independent of enzymatic activity. Our results propose reconsideration of the mechanism of antiviral activity against the flavivirus replication of ChOAS-L.