Structures of human ADAR2 bound to dsRNA reveal base-flipping mechanism and basis for site selectivity.
Publication Type:Journal Article
Source:Nat Struct Mol Biol, Volume 23, Issue 5, p.426-33 (2016)
Keywords:Adenosine Deaminase, Base Sequence, Biocatalysis, Catalytic Domain, Crystallography, X-Ray, Humans, Hydrogen Bonding, Kinetics, Models, Molecular, Protein Binding, RNA, Double-Stranded, RNA-Binding Proteins, Substrate Specificity
<p>Adenosine deaminases acting on RNA (ADARs) are editing enzymes that convert adenosine to inosine in duplex RNA, a modification reaction with wide-ranging consequences in RNA function. Understanding of the ADAR reaction mechanism, the origin of editing-site selectivity, and the effect of mutations is limited by the lack of high-resolution structural data for complexes of ADARs bound to substrate RNAs. Here we describe four crystal structures of the human ADAR2 deaminase domain bound to RNA duplexes bearing a mimic of the deamination reaction intermediate. These structures, together with structure-guided mutagenesis and RNA-modification experiments, explain the basis of the ADAR deaminase domain's dsRNA specificity, its base-flipping mechanism, and its nearest-neighbor preferences. In addition, we identified an ADAR2-specific RNA-binding loop near the enzyme active site, thus rationalizing differences in selectivity observed between different ADARs. Finally, our results provide a structural framework for understanding the effects of ADAR mutations associated with human disease.</p>