Structural characterisation of Spinach Ribulose-1,5-Bisphosphate carboxylase/oxygenase activase isoforms reveals hexameric assemblies with increased thermal stability

Most plants contain two isoforms of Rubisco activase, a chloroplast protein that maintains the activity of Rubisco during photosynthesis. The longer (α-) Rubisco activase 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 characterised the arrangement of the different spinach (Spinacia oleracea) isoforms in solution, and show how the presence of nucleotides changes the oligomeric state. While the shorter (β-) isoform from both tobacco (Nicotiana tabacum) and spinach tend to form a range of oligomers in solution, the size of which which are relatively unaffected by the addition of nucleotide, the spinach α-isoform assembles as a hexamer in the presence of adenosine-5'-(3-thiotriphosphate) (ATPγS). These hexamers have significantly higher heat stability, and may play a role in optimising photosynthesis in 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 ATP hydrolysis, suggesting that a propensity for hexamer formation may not necessarily be correlated with activity. Mod...
Source: BJ Energy - Category: Biochemistry Authors: Tags: BJ Plant Source Type: research