title: Crystal structure of Mil (Mth680): internal duplication and similarity between the Imp4/Brix domain and the anticodon-binding domain of class IIa aminoacyl-tRNA synthetases.
abstract: Proteins of the Imp4/Brix superfamily are involved in ribosomal RNA processing, an essential function in all cells. We report the first structure of an Imp4/Brix superfamily protein, the Mil (for Methanothermobacter thermautotrophicus Imp4-like) protein (gene product Mth680), from the archaeon M. thermautotrophicus. The amino- and carboxy-terminal halves of Mil show significant structural similarity to one another, suggesting an origin by means of an ancestral duplication. Both halves show the same fold as the anticodon-binding domain of class IIa aminoacyl-tRNA synthetases, with greater conservation seen in the N-terminal half. This structural similarity, together with the charge distribution in Mil, suggests that Imp4/Brix superfamily proteins could bind single-stranded segments of RNA along a concave surface formed by the N-terminal half of their beta-sheet and a central alpha-helix. The crystal structure of Mil is incompatible with the presence, in the Imp4/Brix domain, of a helix-turn-helix motif that was proposed to comprise the RNA-binding moiety of the Imp4/Brix proteins.
authors.affiliation: York Structural Biology Laboratory, Chemistry Department, University of York, York YO10 5YW, UK.
authors.forename: Chyan Leong
authors.initials: CL
authors.lastname: Ng
authors.forename: David
authors.initials: D
authors.lastname: Waterman
authors.forename: Eugene V
authors.initials: EV
authors.lastname: Koonin
authors.forename: Alfred A
authors.initials: AA
authors.lastname: Antson
authors.forename: Miguel
authors.initials: M
authors.lastname: Ortiz-Lombardía
mesh_terms: D000595:Amino Acid Sequence; D000604:Amino Acyl-tRNA Synthetases / Q000737:chemistry*; D019843:Archaeal Proteins / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D017013:Methanobacteriaceae / Q000737:chemistry* / Q000201:enzymology / Q000378:metabolism; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D012313:RNA / Q000378:metabolism
chemical_list: D019843:Archaeal Proteins; D012313:RNA; D000604:Amino Acyl-tRNA Synthetases