Molecular Mechanisms for the Adaptive Switching Between the OAS/RNase L and OASL/RIG-I Pathways in Birds and Mammals.
Rong E , Wang X , Chen H , Yang C, Hu J, Liu W, Wang Z , Chen X , Zheng H , Pu J , Sun H , Smith J , Burt DW , Liu J , Li N , Huang Y .
Front Immunol. 2018 Jun 20;9:1398. doi: 10.3389/fimmu.2018.01398. eCollection 2018.

Abstract
Host cells develop the OAS/RNase L [2'-5'-oligoadenylate synthetase (OAS)/ribonuclease L] system to degrade cellular and viral RNA, and/or the OASL/RIG-I (2'-5'-OAS like/retinoic acid inducible protein I) system to enhance RIG-I-mediated IFN induction, thus providing the first line of defense against viral infection. The 2'-5'-OAS-like (OASL) protein may activate the OAS/RNase L system using its typical OAS-like domain (OLD) or mimic the K63-linked pUb to enhance antiviral activity of the OASL/RIG-I system using its two tandem ubiquitin-like domains (UBLs). We first describe that divergent avian (duck and ostrich) OASL inhibit the replication of a broad range of RNA viruses by activating and magnifying the OAS/RNase L pathway in a UBL-dependent manner. This is in sharp contrast to mammalian enzymatic OASL, which activates and magnifies the OAS/RNase L pathway in a UBL-independent manner, similar to 2'-5'-oligoadenylate synthetase 1 (OAS1). We further show that both avian and mammalian OASL can reversibly exchange to activate and magnify the OAS/RNase L and OASL/RIG-I system by introducing only three key residues, suggesting that ancient OASL possess 2-5A [px5'A(2'p5'A)n; x?=?1-3; n?≥?2] activity and has functionally switched to the OASL/RIG-I pathway recently. Our findings indicate the molecular mechanisms involved in the switching of avian and mammalian OASL molecules to activate and enhance the OAS/RNase L and OASL/RIG-I pathways in response to infection by RNA viruses.
KEYWORDS:
OAS/RNase L pathway; OASL; OASL/RIG-I pathway; birds; mammals