title: Identification of the active sites in the methyltransferases of a transcribing dsRNA virus.
abstract: Many double-stranded RNA (dsRNA) viruses are capable of transcribing and capping RNA within a stable icosahedral viral capsid. The turret of turreted dsRNA viruses belonging to the family Reoviridae is formed by five copies of the turret protein, which contains domains with both 7-N-methyltransferase and 2'-O-methyltransferase activities, and serves to catalyze the methylation reactions during RNA capping. Cypovirus of the family Reoviridae provides a good model system for studying the methylation reactions in dsRNA viruses. Here, we present the structure of a transcribing cypovirus to a resolution of ~3.8Å by cryo-electron microscopy. The binding sites for both S-adenosyl-L-methionine and RNA in the two methyltransferases of the turret were identified. Structural analysis of the turret in complex with RNA revealed a pathway through which the RNA molecule reaches the active sites of the two methyltransferases before it is released into the cytoplasm. The pathway shows that RNA capping reactions occur in the active sites of different turret protein monomers, suggesting that RNA capping requires concerted efforts by at least three turret protein monomers. Thus, the turret structure provides novel insights into the precise mechanisms of RNA methylation.
authors.affiliation: College of Physics and Information Science, Hunan Normal University, 36 Lushan Road, Changsha, Hunan 410081, China.
authors.forename: Bin
authors.initials: B
authors.lastname: Zhu
authors.affiliation: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, China; University of the Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Chongwen
authors.initials: C
authors.lastname: Yang
authors.affiliation: College of Physics and Information Science, Hunan Normal University, 36 Lushan Road, Changsha, Hunan 410081, China. Electronic address: hrliu@hunnu.edu.cn.
authors.forename: Hongrong
authors.initials: H
authors.lastname: Liu
authors.affiliation: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, China. Electronic address: lingpengcheng@moon.ibp.ac.cn.
authors.forename: Lingpeng
authors.initials: L
authors.lastname: Cheng
authors.affiliation: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, China; University of the Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Feng
authors.initials: F
authors.lastname: Song
authors.affiliation: College of Physics and Information Science, Hunan Normal University, 36 Lushan Road, Changsha, Hunan 410081, China.
authors.forename: Songjun
authors.initials: S
authors.lastname: Zeng
authors.affiliation: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, China.
authors.forename: Xiaojun
authors.initials: X
authors.lastname: Huang
authors.affiliation: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, China.
authors.forename: Gang
authors.initials: G
authors.lastname: Ji
authors.affiliation: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, China.
authors.forename: Ping
authors.initials: P
authors.lastname: Zhu
mesh_terms: D020134:Catalytic Domain / Q000235:genetics; D008780:Methyltransferases / Q000737:chemistry* / Q000235:genetics; D008958:Models, Molecular; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D012330:RNA, Double-Stranded / Q000235:genetics*; D012367:RNA, Viral / Q000235:genetics*; D012087:Reoviridae / Q000201:enzymology* / Q000235:genetics; D014158:Transcription, Genetic; D054334:Viral Regulatory and Accessory Proteins / Q000737:chemistry* / Q000235:genetics
chemical_list: D012330:RNA, Double-Stranded; D012367:RNA, Viral; D054334:Viral Regulatory and Accessory Proteins; D008780:Methyltransferases
keywords: RNA capping; RNA methyltransferase; Reoviridae; dsRNA virus