|Portis Jr, Archie|
Submitted to: Plant Biology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 2/28/2005
Publication Date: 7/16/2005
Citation: Li, C., Salvucci, M.E., Portis Jr, A.R. 2005. Species specificity of rubisco activase is determined by two amino acids in its sensor 2 domain [abstract]. Plant Biology Annual Meeting. Paper No. 257. Available: http://abstracts.aspb.org/pb2005/public/P43/7154.html. Interpretive Summary: Rubisco (ribulose 1,5-bisphosphate carboxylase/oxygenase) activase is a chloroplast protein that facilitates the activation of Rubisco and maintains its activity by releasing various sugar phosphate inhibitors (e.g. RuBP) that tightly bind to it. The recognition of Rubisco by activase is specific within the family Solanaceae, in that Rubisco can only be effectively activated by activases from within this family, whereas Rubiscos and activases from a variety of non-solanaceous plants such as spinach and barley, and even an algae, Chlamydomonas, are capable of interacting with each other.
Technical Abstract: Rubisco activase belongs to a family of AAA+ proteins within which some members use a 'Sensor 2' domain for substrate recognition. To examine the role of this domain in activase, we constructed two chimeric activases by interchanging a region including Sensor 2 domain between spinach and tobacco activase. Spinach chimeric activase could activate neither spinach nor tobacco Rubisco very well. In contrast tobacco chimeric activase activated spinach Rubisco far better than tobacco Rubisco, similar to spinach activase. A point mutation (K311D) in tobacco chimeric activase abolished its preference to better activate spinach Rubisco. Mutation of this residue (D311K) in tobacco activase resulted in activation of both spinach and tobacco Rubisco. A double mutation in tobacco activase (D311K / L314V), shifted the activation preference toward spinach Rubisco. Corresponding mutations in cotton activase also confirmed the involvement of these two residues in substrate recognition. Activation by the tobacco activase mutants was also examined with Chlamydomonas Rubisco wild type, which prefers spinach activase, and mutants P89R and D94K which prefer tobacco activase. D311K tobacco activase activated wild-type and P89R Chlamydomonas Rubisco, but activation of D94K Rubisco was low. L314V tobacco activase only activated D94K Chlamydomonas Rubisco. Introduction of both mutations into tobacco activase allowed better activation of the wild-type Chlamydomonas Rubisco than either P89R or D94K, mimicking spinach activase. These results indicate a direct interaction between the N-terminus of Rubisco and the Sensor 2 domain of activase. The data also suggest that this interaction involves specific residue pairs, Rubisco-94 with activase-311 and Rubisco-89 with activase-314.