title: The structure of a nucleolytic ribozyme that employs a catalytic metal ion.
abstract: The TS ribozyme (originally called "twister sister") is a catalytic RNA. We present a crystal structure of the ribozyme in a pre-reactive conformation. Two co-axial helical stacks are organized by a three-way junction and two tertiary contacts. Five divalent metal ions are directly coordinated to RNA ligands, making important contributions to the RNA architecture. The scissile phosphate lies in a quasihelical loop region that is organized by a network of hydrogen bonding. A divalent metal ion is directly bound to the nucleobase 5' to the scissile phosphate, with an inner-sphere water molecule positioned to interact with the O2' nucleophile. The rate of ribozyme cleavage correlated in a log-linear manner with divalent metal ion pKa, consistent with proton transfer in the transition state, and we propose that the bound metal ion is a likely general base for the cleavage reaction. Our data indicate that the TS ribozyme functions predominantly as a metalloenzyme.
authors.affiliation: Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee, UK.
authors.forename: Yijin
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee, UK.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Wilson
authors.affiliation: Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee, UK.
authors.forename: David M J
authors.initials: DMJ
authors.lastname: Lilley
mesh_terms: D055162:Biocatalysis; D007477:Ions / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism*; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D016337:RNA, Catalytic / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D007477:Ions; D016337:RNA, Catalytic; D008274:Magnesium