title: Activation of interspecies-hybrid Rubisco enzymes to assess different models for the Rubisco-Rubisco activase interaction.
abstract: Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is prone to inactivation from non-productive binding of sugar-phosphates. Reactivation of Rubisco requires conformational remodeling by a specific chaperone, Rubisco activase. Rubisco activase from tobacco and other plants in the family Solanaceae is an inefficient activator of Rubisco from non-Solanaceae plants and from the green alga Chlamydomonas reinhardtii. To determine if the Rubisco small subunit plays a role in the interaction with Rubisco activase, a hybrid Rubisco (SSNT) composed of tobacco small subunits and Chlamydomonas large subunits was constructed. The SSNT hybrid, like other hybrid Rubiscos containing plant small subunits, supported photoautotrophic growth in Chlamydomonas, but growth in air was much slower than for cells containing wild-type Rubisco. The kinetic properties of the SSNT hybrid Rubisco were similar to the wild-type enzyme, indicating that the poor growth in air was probably caused by disruption of pyrenoid formation and the consequent impairment of the CO2concentrating mechanism. Recombinant Rubisco activase from Arabidopsis activated the SSNT hybrid Rubisco and hybrid Rubiscos containing spinach and Arabidopsis small subunits at rates similar to the rates with wild-type Rubisco. However, none of the hybrid Rubiscos was activated by tobacco Rubisco activase. That replacement of Chlamydomonas small subunits with plant small subunits does not affect the species-specific interaction between Rubisco and Rubisco activase suggests that the association is not dominated by the small subunits that surround the Rubisco central solvent channel. Therefore, the geometry of a side-on binding mode is more consistent with the data than a top-on or ring-stacking binding mode.
authors.affiliation: Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ, 85287, USA.
authors.forename: Rebekka M
authors.initials: RM
authors.lastname: Wachter
authors.forename: Michael E
authors.initials: ME
authors.lastname: Salvucci
authors.forename: A Elizabete
authors.initials: AE
authors.lastname: Carmo-Silva
authors.forename: Csengele
authors.initials: C
authors.lastname: Barta
authors.forename: Todor
authors.initials: T
authors.lastname: Genkov
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Spreitzer
mesh_terms: D000595:Amino Acid Sequence; D016825:Chlamydomonas reinhardtii / Q000201:enzymology*; D004789:Enzyme Activation; D007700:Kinetics; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000378:metabolism*; D011485:Protein Binding; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism*; D012273:Ribulose-Bisphosphate Carboxylase / Q000737:chemistry / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D014026:Nicotiana / Q000201:enzymology*
chemical_list: D010940:Plant Proteins; D021122:Protein Subunits; D011994:Recombinant Proteins; C054765:rca protein, plant; D012273:Ribulose-Bisphosphate Carboxylase