Most plants contain two isoforms of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activase (Rca), a chloroplast protein that maintains the activity of Rubisco during photosynthesis. The longer (α-) Rca isoform has previously been shown to regulate the activity of Rubisco in response to both the ADP:ATP ratio and redox potential via thioredoxin-f. We have characterized the arrangement of the different spinach (Spinacia oleracea) isoforms in solution, and show how the presence of nucleotides changes the oligomeric state. Although the shorter (β-) isoform from both tobacco (Nicotiana tabacum) and spinach tend to form a range of oligomers in solution, the size of which are relatively unaffected by the addition of nucleotide, the spinach α-isoform assembles as a hexamer in the presence of adenosine 5′-[γ-thio]triphosphate (ATPγS). These hexamers have significantly higher heat stability, and may play a role in optimizing photosynthesis at higher temperatures. Hexamers were also observed for mixtures of the two isoforms, suggesting that the α-isoform can act as a structural scaffold for hexamer formation by the β-isoform. Additionally, it is shown that a variant of the tobacco β-isoform acts in a similar fashion to the α-isoform of spinach, forming thermally stable hexamers in the presence of ATPγS. Both isoforms had similar rates of ATP hydrolysis, suggesting that a propensity for hexamer formation may not necessarily be correlated with activity. Modelling of the hexameric structures suggests that although the N-terminus of Rca forms a highly dynamic, extended structure, the C-terminus is located adjacent to the intersubunit interface.
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Research Article|
December 05 2014
Characterization of spinach ribulose-1,5-bisphosphate carboxylase/oxygenase activase isoforms reveals hexameric assemblies with increased thermal stability
Jeremy R. Keown;
Jeremy R. Keown
*Biomolecular Interactions Centre and School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch 8020, New Zealand
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Frederick Grant Pearce
Frederick Grant Pearce
1
*Biomolecular Interactions Centre and School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch 8020, New Zealand
1To whom correspondence should be addressed (email grant.pearce@canterbury.ac.nz).
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Publisher: Portland Press Ltd
Received:
June 03 2014
Revision Received:
September 16 2014
Accepted:
September 23 2014
Accepted Manuscript online:
September 23 2014
Online ISSN: 1470-8728
Print ISSN: 0264-6021
© The Authors Journal compilation © 2014 Biochemical Society
2014
Biochem J (2014) 464 (3): 413–423.
Article history
Received:
June 03 2014
Revision Received:
September 16 2014
Accepted:
September 23 2014
Accepted Manuscript online:
September 23 2014
Citation
Jeremy R. Keown, Frederick Grant Pearce; Characterization of spinach ribulose-1,5-bisphosphate carboxylase/oxygenase activase isoforms reveals hexameric assemblies with increased thermal stability. Biochem J 15 December 2014; 464 (3): 413–423. doi: https://doi.org/10.1042/BJ20140676
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