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Structural mechanism of sensing long dsRNA via a noncatalytic domain in human oligoadenylate synthetase 3.

ABSTRACT: The mammalian innate immune system uses several sensors of double-stranded RNA (dsRNA) to develop the interferon response. Among these sensors are dsRNA-activated oligoadenylate synthetases (OAS), which produce signaling 2',5'-linked RNA molecules (2-5A) that activate regulated RNA decay in mammalian tissues. Different receptors from the OAS family contain one, two, or three copies of the 2-5A synthetase domain, which in several instances evolved into pseudoenzymes. The structures of the pseudoenzymatic domains and their roles in sensing dsRNA are unknown. Here we present the crystal structure of the first catalytically inactive domain of human OAS3 (hOAS3.DI) in complex with a 19-bp dsRNA, determined at 2.0-Å resolution. The conformation of hOAS3.DI is different from the apo- and the dsRNA-bound states of the catalytically active homolog, OAS1, reported previously. The unique conformation of hOAS3.DI disables 2-5A synthesis by placing the active site residues nonproductively, but favors the binding of dsRNA. Biochemical data show that hOAS3.DI is essential for activation of hOAS3 and serves as a dsRNA-binding module, whereas the C-terminal domain DIII carries out catalysis. The location of the dsRNA-binding domain (DI) and the catalytic domain (DIII) at the opposite protein termini makes hOAS3 selective for long dsRNA. This mechanism relies on the catalytic inactivity of domain DI, revealing a surprising role of pseudoenzyme evolution in dsRNA surveillance.

SUBMITTER: Donovan J

PROVIDER: S-EPMC4386348 | biostudies-literature | 2015 Mar

REPOSITORIES: biostudies-literature

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Structural mechanism of sensing long dsRNA via a noncatalytic domain in human oligoadenylate synthetase 3.

Donovan Jesse J Whitney Gena G Rath Sneha S Korennykh Alexei A

Proceedings of the National Academy of Sciences of the United States of America 20150316 13

The mammalian innate immune system uses several sensors of double-stranded RNA (dsRNA) to develop the interferon response. Among these sensors are dsRNA-activated oligoadenylate synthetases (OAS), which produce signaling 2',5'-linked RNA molecules (2-5A) that activate regulated RNA decay in mammalian tissues. Different receptors from the OAS family contain one, two, or three copies of the 2-5A synthetase domain, which in several instances evolved into pseudoenzymes. The structures of the pseudoe ...[more]

PMID: 25775560

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Project description:BackgroundOligoadenylate synthetases (OASs) are widely distributed in Metazoa including sponges, fish, reptiles, birds and mammals and show large variation, with one to twelve members in any given species. Upon double-stranded RNA (dsRNA) binding, avian and mammalian OASs generate the second messenger 2'-5'-linked oligoadenylate (2-5A), which activates ribonuclease L (RNaseL) and blocks viral replication. However, how Metazoa shape their OAS repertoires to keep evolutionary balance to virus infection is largely unknown. We performed comprehensive phylogenetic and functional analyses of OAS genes from evolutionarily lower to higher Metazoa to demonstrate how the OAS repertoires have developed anti-viral activity and diversified their functions.ResultsAncient Metazoa harbor OAS genes, but lack both upstream and downstream genes of the OAS-related pathways, indicating that ancient OASs are not interferon-induced genes involved in the innate immune system. Compared to OASs of ancient Metazoa (i.e. sponge), the corresponding ones of higher Metazoa present an increasing number of basic residues on the OAS/dsRNA interaction interface. Such an increase of basic residues might improve their binding affinity to dsRNA. Moreover, mutations of functional residues in the active pocket might lead to the fact that higher Metazoan OASs lose the ability to produce 3'-5'-linked oligoadenylate (3-5A) and turn into specific 2-5A synthetases. In addition, we found that multiple rounds of gene duplication and domain coupling events occurred in the OAS family and mutations at functionally critical sites were observed in most new OAS members.ConclusionsWe propose a model for the expansion of OAS members and provide comprehensive evidence of subsequent neo-functionalization and sub-functionalization. Our observations lay the foundation for interrogating the evolutionary transition of ancient OAS genes to host defense genes and provide important information for exploring the unknown function of the OAS gene family.

Dataset Information

Structural mechanism of sensing long dsRNA via a noncatalytic domain in human oligoadenylate synthetase 3.

Publications

Structural mechanism of sensing long dsRNA via a noncatalytic domain in human oligoadenylate synthetase 3.

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