title: Structural changes associated with the acute thermal instability of Rubisco activase.
abstract: Inhibition of photosynthesis by heat has been linked to the instability of the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) chaperone, Rubisco activase. Examination of the recombinant enzyme showed that ADP and ATP protected against inactivation, whereas Mg(2+) promoted inactivation. Heating caused aggregation of Rubisco activase characterized by disruption of secondary structure content and formation of insoluble protein. In contrast, incubation at room temperature without nucleotide caused the active approximately 660 kDa protein to form a soluble, but inactive aggregate of > 2 x 10(6) Da. Circular dichroism (CD) spectroscopy and fluorescence established that structural perturbations in the aggregate did not reduce alpha-helical content significantly. Differences in the thermal stability between wild type and mutant Rubisco activase were observed for the recombinant proteins and when the proteins were expressed in transgenic Arabidopsis. That the sensitivity of these plants to heat differs indicates that the thermal instability of Rubisco activase is a main determinant of the temperature-sensitivity of photosynthesis.
authors.affiliation: US Department of Agriculture-Agricultural Research Service, Arid-Land Agricultural Research Center, Maricopa, AZ 85139, USA. csengele.barta@ars.usda.gov
authors.forename: Csengele
authors.initials: C
authors.lastname: Barta
authors.forename: Alison M
authors.initials: AM
authors.lastname: Dunkle
authors.forename: Rebekka M
authors.initials: RM
authors.lastname: Wachter
authors.forename: Michael E
authors.initials: ME
authors.lastname: Salvucci
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002942:Circular Dichroism; D004789:Enzyme Activation / Q000187:drug effects; D004795:Enzyme Stability / Q000187:drug effects; D006358:Hot Temperature; D008274:Magnesium / Q000494:pharmacology; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010788:Photosynthesis; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D011489:Protein Denaturation; D055503:Protein Multimerization / Q000187:drug effects; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism; D013816:Thermodynamics
chemical_list: D029681:Arabidopsis Proteins; D050505:Mutant Proteins; D010940:Plant Proteins; D011994:Recombinant Proteins; C054765:rca protein, plant; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D012273:Ribulose-Bisphosphate Carboxylase; D008274:Magnesium