title: Small oligomers of ribulose-bisphosphate carboxylase/oxygenase (Rubisco) activase are required for biological activity.
abstract: Ribulose-bisphosphate carboxylase/oxygenase (Rubisco) activase uses the energy from ATP hydrolysis to remove tight binding inhibitors from Rubisco, thus playing a key role in regulating photosynthesis in plants. Although several structures have recently added much needed structural information for different Rubisco activase enzymes, the arrangement of these subunits in solution remains unclear. In this study, we use a variety of techniques to show that Rubisco activase forms a wide range of structures in solution, ranging from monomers to much higher order species, and that the distribution of these species is highly dependent on protein concentration. The data support a model in which Rubisco activase forms an open spiraling structure rather than a closed hexameric structure. At protein concentrations of 1 μM, corresponding to the maximal activity of the enzyme, Rubisco activase has an oligomeric state of 2-4 subunits. We propose a model in which Rubisco activase requires at least 1 neighboring subunit for hydrolysis of ATP.
authors.affiliation: Biomolecular Interactions Centre and School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand.
authors.forename: Jeremy R
authors.initials: JR
authors.lastname: Keown
authors.forename: Michael D W
authors.initials: MD
authors.lastname: Griffin
authors.forename: Haydyn D T
authors.initials: HD
authors.lastname: Mertens
authors.forename: F Grant
authors.initials: FG
authors.lastname: Pearce
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D004789:Enzyme Activation; D006868:Hydrolysis; D008958:Models, Molecular; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D053838:Scattering, Small Angle; D012996:Solutions / Q000737:chemistry; D014026:Nicotiana / Q000201:enzymology / Q000235:genetics; D014961:X-Ray Diffraction
chemical_list: D010940:Plant Proteins; D021122:Protein Subunits; D012996:Solutions; C054765:rca protein, plant; D000255:Adenosine Triphosphate
keywords: AAA+ Protein; Analytical Ultracentrifugation; Protein Assembly; Protein Complexes; Protein Structure; Rubisco Activase; X-ray Scattering