title: Insights into eukaryotic Rubisco assembly - crystal structures of RbcX chaperones from Arabidopsis thaliana.
abstract: BACKGROUND
  Chloroplasts were formed by uptake of cyanobacteria into eukaryotic cells ca. 1.6 billion years ago. During evolution most of the cyanobacterial genes were transferred from the chloroplast to the nuclear genome. The rbcX gene, encoding an assembly chaperone required for Rubisco biosynthesis in cyanobacteria, was duplicated. Here we demonstrate that homologous eukaryotic chaperones (AtRbcX1 and AtRbcX2) demonstrate different affinities for the C-terminus of Rubisco large subunit and determine their crystal structures.
  
  
  METHODS
  Three-dimensional structures of AtRbcX1 and AtRbcX2 were resolved by the molecular replacement method. Equilibrium binding constants of the C-terminal RbcL peptide by AtRbcX proteins were determined by spectrofluorimetric titration. The binding mode of RbcX-RbcL was predicted using molecular dynamic simulation.
  
  
  RESULTS
  We provide crystal structures of both chaperones from Arabidopsis thaliana providing the first structural insight into Rubisco assembly chaperones form higher plants. Despite the low sequence homology of eukaryotic and cyanobacterial Rubisco chaperones the eukaryotic counterparts exhibit surprisingly high similarity of the overall fold to previously determined prokaryotic structures. Modeling studies demonstrate that the overall mode of the binding of RbcL peptide is conserved among these proteins. As such, the evolution of RbcX chaperones is another example of maintaining conserved structural features despite significant drift in the primary amino acid sequence.
  
  
  CONCLUSIONS
  The presented results are the approach to elucidate the role of RbcX proteins in Rubisco assembly in higher plants.
authors.affiliation: Laboratory of Biophysics, Faculty of Biotechnology, University of Wroclaw, Przybyszewskiego 63/77, 51-148 Wroclaw, Poland.
authors.forename: Piotr
authors.initials: P
authors.lastname: Kolesinski
authors.forename: Przemyslaw
authors.initials: P
authors.lastname: Golik
authors.forename: Przemyslaw
authors.initials: P
authors.lastname: Grudnik
authors.forename: Janusz
authors.initials: J
authors.lastname: Piechota
authors.forename: Michał
authors.initials: M
authors.lastname: Markiewicz
authors.forename: Miroslaw
authors.initials: M
authors.lastname: Tarnawski
authors.forename: Grzegorz
authors.initials: G
authors.lastname: Dubin
authors.forename: Andrzej
authors.initials: A
authors.lastname: Szczepaniak
mesh_terms: D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins / Q000737:chemistry*; D060365:Chloroplast Proteins / Q000737:chemistry*; D003460:Crystallization; D018832:Molecular Chaperones / Q000737:chemistry*; D008969:Molecular Sequence Data; D011487:Protein Conformation; D055503:Protein Multimerization; D055550:Protein Stability; D012273:Ribulose-Bisphosphate Carboxylase / Q000737:chemistry*
chemical_list: D029681:Arabidopsis Proteins; D060365:Chloroplast Proteins; D018832:Molecular Chaperones; C568500:RbcX1 protein, Arabidopsis; C568501:RbcX2 protein, Arabidopsis; D012273:Ribulose-Bisphosphate Carboxylase