title: Three-dimensional solution structures of the chromodomains of cpSRP43.
abstract: Chloroplasts contain a unique signal recognition particle (cpSRP). Unlike the cytoplasmic forms, the cpSRP lacks RNA but contains a conserved 54-kDa GTPase and a novel 43-kDa subunit (cpSRP43). Recently, three functionally distinct chromodomains (CDs) have been identified in cpSRP43. In the present study, we report the three-dimensional solution structures of the three CDs (CD1, CD2, and CD3) using a variety of triple resonance NMR experiments. The structure of CD1 consists of a triple-stranded beta-sheet segment. The C-terminal helical segment typically found in the nuclear chromodomains is absent in CD1. The secondary structural elements in CD2 and CD3 include a triple-stranded antiparallel beta-sheet and a C-terminal helix. Interestingly, the orientation of the C-terminal helix is significantly different in the structures of CD2 and CD3. Critical comparison of the structures of the chromodomains of cpSRP43 with those found in nuclear chromodomain proteins revealed that the diverse protein-protein interactions mediated by the CDs appear to stem from the differences that exist in the surface charge potentials of each CD. Results of isothermal titration calorimetry experiments confirmed that only CD2 is involved in binding to cpSRP54. The negatively charged C-terminal helix in CD2 possibly plays a crucial role in the cpSRP54-cpSRP43 interaction.
authors.affiliation: Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701, USA.
authors.forename: Vaithiyalingam
authors.initials: V
authors.lastname: Sivaraja
authors.forename: Thallapuranam Krishnaswamy Suresh
authors.initials: TK
authors.lastname: Kumar
authors.forename: Philominathan Sagaya Theresa
authors.initials: PS
authors.lastname: Leena
authors.forename: An-ni
authors.initials: AN
authors.lastname: Chang
authors.forename: Chitturi
authors.initials: C
authors.lastname: Vidya
authors.forename: Robyn L
authors.initials: RL
authors.lastname: Goforth
authors.forename: Dakshinamurthy
authors.initials: D
authors.lastname: Rajalingam
authors.forename: Kannan
authors.initials: K
authors.lastname: Arvind
authors.forename: Jiang-Liang
authors.initials: JL
authors.lastname: Ye
authors.forename: Jonathan
authors.initials: J
authors.lastname: Chou
authors.forename: Ralph
authors.initials: R
authors.lastname: Henry
authors.forename: Chin
authors.initials: C
authors.lastname: Yu
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001665:Binding Sites; D002151:Calorimetry; D060365:Chloroplast Proteins; D002736:Chloroplasts / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D045342:Light-Harvesting Protein Complexes; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D045322:Photosynthetic Reaction Center Complex Proteins; D010940:Plant Proteins; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012313:RNA / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D018271:Signal Recognition Particle / Q000737:chemistry / Q000502:physiology*
chemical_list: D060365:Chloroplast Proteins; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D010940:Plant Proteins; D018271:Signal Recognition Particle; D012313:RNA