- View final version: Identification of interactions between abscisic acid and ribulose-1,5-bisphosphate carboxylase/oxygenase (PDF, 1 MB)
|DOI||Resolve DOI: https://doi.org/10.1371/journal.pone.0133033|
|Author||Search for: Galka, Marek M.1; Search for: Rajagopalan, Nandhakishore (Kishore)1; Search for: Buhrow, Leann M.1; Search for: Nelson, Kenneth (Ken)1; Search for: Switala, Jacek; Search for: Cutler, Adrian J.1; Search for: Palmer, David R. J.; Search for: Loewen, Peter C.; Search for: Abrams, Suzanne R (Sue)1; Search for: Loewen, Michele C.1|
- National Research Council of Canada. Aquatic and Crop Resource Development
|Subject||abscisic acid; hormone binding protein; oxygenase; ribulose 1,5 bisphosphate oxygenase; ribulosebisphosphate carboxylase; unclassified drug; vegetable protein; binding affinity; catalysis; comparative study; computer model; electron; enzyme activation; enzyme active site; enzyme activity; enzyme inhibition; enzyme structure; enzyme substrate; isothermal titration calorimetry; molecular docking; protein protein interaction; spinach; structure analysis; validation study|
Abscisic acid ((+)-ABA) is a phytohormone involved in the modulation of developmental processes and stress responses in plants. A chemical proteomics approach using an ABA mimetic probe was combined with in vitro assays, isothermal titration calorimetry (ITC), xray crystallography and in silico modelling to identify putative (+)-ABA binding-proteins in crude extracts of Arabidopsis thaliana. Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) was identified as a putative ABA-binding protein. Radiolabelled-binding assays yielded a Kd of 47 nM for (+)-ABA binding to spinach Rubisco, which was validated by ITC, and found to be similar to reported and experimentally derived values for the native ribulose- 1,5-bisphosphate (RuBP) substrate. Functionally, (+)-ABA caused only weak inhibition of Rubisco catalytic activity (Ki of 2.1 mM), but more potent inhibition of Rubisco activation (Ki of ~ 130 μM). Comparative structural analysis of Rubisco in the presence of (+)-ABA with RuBP in the active site revealed only a putative low occupancy (+)-ABA binding site on the surface of the large subunit at a location distal from the active site. However, subtle distortions in electron density in the binding pocket and in silico docking support the possibility of a higher affinity (+)-ABA binding site in the RuBP binding pocket. Overall we conclude that (+)-ABA interacts with Rubisco. While the low occupancy (+)-ABA binding site and weak non-competitive inhibition of catalysis may not be relevant, the high affinity site may allow ABA to act as a negative effector of Rubisco activation.
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