title: Structural basis for viral 5'-PPP-RNA recognition by human IFIT proteins.
abstract: Interferon-induced proteins with tetratricopeptide repeats (IFITs) are innate immune effector molecules that are thought to confer antiviral defence through disruption of protein-protein interactions in the host translation-initiation machinery. However, it was recently discovered that IFITs can directly recognize viral RNA bearing a 5'-triphosphate group (PPP-RNA), which is a molecular signature that distinguishes it from host RNA. Here we report crystal structures of human IFIT5, its complex with PPP-RNAs, and an amino-terminal fragment of IFIT1. The structures reveal a new helical domain that houses a positively charged cavity designed to specifically engage only single-stranded PPP-RNA, thus distinguishing it from the canonical cytosolic sensor of double-stranded viral PPP-RNA, retinoic acid-inducible gene I (RIG-I, also known as DDX58). Mutational analysis, proteolysis and gel-shift assays reveal that PPP-RNA is bound in a non-sequence-specific manner and requires a 5'-overhang of approximately three nucleotides. Abrogation of PPP-RNA binding in IFIT1 and IFIT5 was found to cause a defect in the antiviral response by human embryonic kidney cells. These results demonstrate the mechanism by which IFIT proteins selectively recognize viral RNA, and lend insight into their downstream effector function.
authors: Department of Biochemistry, Groupe de Recherche Axé sur la Structure des Protéines, McGill University, Montreal, Quebec H3G 0B1, Canada.
authors: Yazan M
authors: YM
authors: Abbas
authors: Andreas
authors: A
authors: Pichlmair
authors: Maria W
authors: MW
authors: Górna
authors: Giulio
authors: G
authors: Superti-Furga
authors: Bhushan
authors: B
authors: Nagar
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D020816:Amino Acid Motifs; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D007113:Immunity, Innate / Q000276:immunology; D008958:Models, Molecular; D009363:Neoplasm Proteins / Q000737:chemistry* / Q000378:metabolism*; D010766:Phosphorylation; D011487:Protein Conformation; D012367:RNA, Viral / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D016601:RNA-Binding Proteins; D015203:Reproducibility of Results; D013379:Substrate Specificity
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; C484290:IFIT1 protein, human; C110985:IFIT5 protein, human; D009363:Neoplasm Proteins; D012367:RNA, Viral; D016601:RNA-Binding Proteins