title: Characterization of a trifunctional mimivirus mRNA capping enzyme and crystal structure of the RNA triphosphatase domain.
abstract: The RNA triphosphatase (RTPase) components of the mRNA capping apparatus are a bellwether of eukaryal taxonomy. Fungal and protozoal RTPases belong to the triphosphate tunnel metalloenzyme (TTM) family, exemplified by yeast Cet1. Several large DNA viruses encode metal-dependent RTPases unrelated to the cysteinyl-phosphatase RTPases of their metazoan host organisms. The origins of DNA virus RTPases are unclear because they are structurally uncharacterized. Mimivirus, a giant virus of amoeba, resembles poxviruses in having a trifunctional capping enzyme composed of a metal-dependent RTPase module fused to guanylyltransferase (GTase) and guanine-N7 methyltransferase domains. The crystal structure of mimivirus RTPase reveals a minimized tunnel fold and an active site strikingly similar to that of Cet1. Unlike homodimeric fungal RTPases, mimivirus RTPase is a monomer. The mimivirus TTM-type RTPase-GTase fusion resembles the capping enzymes of amoebae, providing evidence that the ancestral large DNA virus acquired its capping enzyme from a unicellular host.
authors.affiliation: Molecular Biology Program, Sloan-Kettering Institute, New York, NY 10021, USA.
authors.forename: Delphine
authors.initials: D
authors.lastname: Benarroch
authors.forename: Paul
authors.initials: P
authors.lastname: Smith
authors.forename: Stewart
authors.initials: S
authors.lastname: Shuman
mesh_terms: D017766:Acid Anhydride Hydrolases / Q000737:chemistry* / Q000235:genetics; D000595:Amino Acid Sequence; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004267:DNA Viruses / Q000201:enzymology*; D008780:Methyltransferases / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D009713:Nucleotidyltransferases / Q000737:chemistry* / Q000235:genetics; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D014764:Viral Proteins / Q000737:chemistry* / Q000235:genetics; D000098556:mRNA Guanylyltransferases
chemical_list: D014764:Viral Proteins; D008780:Methyltransferases; D009713:Nucleotidyltransferases; D000098556:mRNA Guanylyltransferases; D017766:Acid Anhydride Hydrolases; C023090:RNA triphosphatase