title: Structure and function of the AAA+ protein CbbX, a red-type Rubisco activase.
abstract: Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) catalyses the fixation of atmospheric CO(2) in photosynthesis, but tends to form inactive complexes with its substrate ribulose 1,5-bisphosphate (RuBP). In plants, Rubisco is reactivated by the AAA(+) (ATPases associated with various cellular activities) protein Rubisco activase (Rca), but no such protein is known for the Rubisco of red algae. Here we identify the protein CbbX as an activase of red-type Rubisco. The 3.0-Å crystal structure of unassembled CbbX from Rhodobacter sphaeroides revealed an AAA(+) protein architecture. Electron microscopy and biochemical analysis showed that ATP and RuBP must bind to convert CbbX into functionally active, hexameric rings. The CbbX ATPase is strongly stimulated by RuBP and Rubisco. Mutational analysis suggests that CbbX functions by transiently pulling the carboxy-terminal peptide of the Rubisco large subunit into the hexamer pore, resulting in the release of the inhibitory RuBP. Understanding Rubisco activation may facilitate efforts to improve CO(2) uptake and biomass production by photosynthetic organisms.
authors: Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany.
authors: Oliver
authors: O
authors: Mueller-Cajar
authors: Mathias
authors: M
authors: Stotz
authors: Petra
authors: P
authors: Wendler
authors: F Ulrich
authors: FU
authors: Hartl
authors: Andreas
authors: A
authors: Bracher
authors: Manajit
authors: M
authors: Hayer-Hartl
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000494:Allosteric Regulation / Q000187:drug effects; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D002245:Carbon Dioxide / Q000378:metabolism; D018360:Crystallography, X-Ray; D004789:Enzyme Activation / Q000187:drug effects; D008958:Models, Molecular; D055503:Protein Multimerization / Q000187:drug effects; D020836:Protein Structure, Quaternary / Q000187:drug effects; D012242:Rhodobacter sphaeroides / Q000201:enzymology*; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism*; D012274:Ribulosephosphates / Q000378:metabolism / Q000494:pharmacology; D013329:Structure-Activity Relationship
chemical_list: D001426:Bacterial Proteins; C104044:CbbX protein, Rhodobacter sphaeroides; D012274:Ribulosephosphates; D002245:Carbon Dioxide; C001933:ribulose-1,5 diphosphate; D000255:Adenosine Triphosphate; D012273:Ribulose-Bisphosphate Carboxylase