title: RNA binding by a novel helical fold of b2 protein from wuhan nodavirus mediates the suppression of RNA interference and promotes b2 dimerization.
abstract: Wuhan nodavirus (WhNV) is a newly identified member of the Nodaviridae family with a bipartite genome of positive-sense RNAs. A nonstructural protein encoded by subgenomic RNA3 of nodaviruses, B2, serves as a potent RNA silencing suppressor (RSS) by sequestering RNA duplexes. We have previously demonstrated that WhNV B2 blocks RNA silencing in cultured Drosophila cells. However, the molecular mechanism by which WhNV B2 functions remains unknown. Here, we successfully established an RNA silencing system in cells derived from Pieris rapae, a natural host of WhNV, by introducing into these cells double-stranded RNA (dsRNA)-expressing plasmids or chemically synthesized small interfering RNAs (siRNAs). Using this system, we revealed that the WhNV B2 protein inhibited Dicer-mediated dsRNA cleavage and the incorporation of siRNA into the RNA-induced silencing complex (RISC) by sequestering dsRNA and siRNA. Based on the modeled B2 3-dimensional structure, serial single alanine replacement mutations and N-terminal deletion analyses showed that the RNA-binding domain of B2 is formed by its helices α2 and α3, while helix α1 mediates B2 dimerization. Furthermore, positive feedback between RNA binding and B2 dimerization was uncovered by gel shift assay and far-Western blotting, revealing that B2 dimerization is required for its binding to RNA, whereas RNA binding to B2 in turn promotes its dimerization. All together, our findings uncovered a novel RNA-binding mode of WhNV B2 and provided evidence that the promotion effect of RNA binding on dimerization exists in a viral RSS protein.
authors: The State Key Laboratory of Life Sciences, College of Life Sciences, Wuhan, Hubei 430072, China.
authors: Nan
authors: N
authors: Qi
authors: Dawei
authors: D
authors: Cai
authors: Yang
authors: Y
authors: Qiu
authors: Jiazheng
authors: J
authors: Xie
authors: Zhaowei
authors: Z
authors: Wang
authors: Jie
authors: J
authors: Si
authors: Jiamin
authors: J
authors: Zhang
authors: Xi
authors: X
authors: Zhou
authors: Yuanyang
authors: Y
authors: Hu
mesh_terms: D000818:Animals; D002460:Cell Line; D024202:Electrophoretic Mobility Shift Assay; D007915:Lepidoptera / Q000821:virology; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D030381:Nodaviridae / Q000502:physiology*; D011485:Protein Binding; D011487:Protein Conformation; D055503:Protein Multimerization; D034622:RNA Interference; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D017384:Sequence Deletion; D017361:Viral Nonstructural Proteins / Q000235:genetics / Q000378:metabolism*; D014779:Virus Replication
chemical_list: D016601:RNA-Binding Proteins; D017361:Viral Nonstructural Proteins