title: Crystal structures of the Arabidopsis thaliana organellar RNA editing factors MORF1 and MORF9.
abstract: In flowering plant plastids and mitochondria, multiple organellar RNA editing factor (MORF/RIP) proteins are required at most sites for efficient C to U RNA editing catalyzed by the RNA editosome. MORF proteins harbor a conserved stretch of residues (MORF-box), form homo- and heteromers and interact with selected PPR (pentatricopeptide repeat) proteins, which recognize each editing site. The molecular function of the MORF-box remains elusive since it shares no sequence similarity with known domains. We determined structures of the A. thaliana mitochondrial MORF1 and chloroplast MORF9 MORF-boxes which both adopt a novel globular fold (MORF domain). Our structures state a paradigmatic model for MORF domains and their specific dimerization via a hydrophobic interface. We cross-validate the interface by yeast two-hybrid studies and pulldown assays employing structure-based mutants. We find a structural similarity of the MORF domain to an N-terminal ferredoxin-like domain (NFLD), which confers RNA substrate positioning in bacterial 4-thio-uracil tRNA synthetases, implying direct RNA contacts of MORF proteins during RNA editing. With the MORF1 and MORF9 structures we elucidate a yet unknown fold, corroborate MORF interaction studies, validate the mechanism of MORF multimerization by structure-based mutants and pave the way towards a complete structural characterization of the plant RNA editosome.
authors.affiliation: Molekulare Botanik, Universität Ulm, 89069 Ulm, Germany.
authors.forename: Sascha
authors.initials: S
authors.lastname: Haag
authors.affiliation: Institut für Chemie und Biochemie, Strukturbiochemie, Freie Universität Berlin, Takustrasse 6, 14195 Berlin, Germany.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Schindler
authors.affiliation: Universität Greifswald, Institut für Biochemie, Molekulare Strukturbiologie, Felix-Hausdorff-Str. 4, 17487 Greifswald, Germany.
authors.forename: Leona
authors.initials: L
authors.lastname: Berndt
authors.affiliation: Molekulare Botanik, Universität Ulm, 89069 Ulm, Germany.
authors.forename: Axel
authors.initials: A
authors.lastname: Brennicke
authors.affiliation: Molekulare Botanik, Universität Ulm, 89069 Ulm, Germany.
authors.forename: Mizuki
authors.initials: M
authors.lastname: Takenaka
authors.affiliation: Institut für Chemie und Biochemie, Strukturbiochemie, Freie Universität Berlin, Takustrasse 6, 14195 Berlin, Germany.
authors.forename: Gert
authors.initials: G
authors.lastname: Weber
mesh_terms: D017360:Arabidopsis / Q000737:chemistry* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000235:genetics; D002736:Chloroplasts / Q000737:chemistry; D018360:Crystallography, X-Ray; D008928:Mitochondria / Q000737:chemistry; D008969:Molecular Sequence Data; D000072417:Protein Domains / Q000235:genetics*; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D017393:RNA Editing / Q000235:genetics; D000067776:RNA Recognition Motif Proteins / Q000737:chemistry* / Q000235:genetics; D016601:RNA-Binding Proteins / Q000737:chemistry*
chemical_list: D029681:Arabidopsis Proteins; C000622450:MORF1 protein, Arabidopsis; C000622451:MORF9 protein, Arabidopsis; D000067776:RNA Recognition Motif Proteins; D016601:RNA-Binding Proteins