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Title: Rubisco activase requires residues in the large subunit N terminus to remodel inhibited plant Rubisco
Authors: Ng, Jediael
Guo, Zhijun
Mueller-Cajar, Oliver
Keywords: Science::Biological sciences
Issue Date: 2020
Source: Ng, J., Guo, Z. & Mueller-Cajar, O. (2020). Rubisco activase requires residues in the large subunit N terminus to remodel inhibited plant Rubisco. Journal of Biological Chemistry, 295(48), 16427-16435.
Project: MOE2016-T2-2-088 
Journal: Journal of Biological Chemistry 
Abstract: The photosynthetic CO2 fixing enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) forms dead-end inhibited complexes while binding multiple sugar phosphates, including its substrate ribulose 1,5-bisphosphate. Rubisco can be rescued from this inhibited form by molecular chaperones belonging to the ATPases associated with diverse cellular activities (AAA+ proteins) termed Rubisco activases (Rcas). The mechanism of green-type Rca found in higher plants has proved elusive, in part because until recently higher-plant Rubiscos could not be expressed recombinantly. Identifying the interaction sites between Rubisco and Rca is critical to formulate mechanistic hypotheses. Toward that end here we purify and characterize a suite of 33 Arabidopsis Rubisco mutants for their ability to be activated by Rca. Mutation of 17 surface-exposed large subunit residues did not yield variants that were perturbed in their interaction with Rca. In contrast, we find that Rca activity is highly sensitive to truncations and mutations in the conserved N terminus of the Rubisco large subunit. Large subunits lacking residues 1-4 are functional Rubiscos but cannot be activated. Both T5A and T7A substitutions result in functional carboxylases that are poorly activated by Rca, indicating the side chains of these residues form a critical interaction with the chaperone. Many other AAA+ proteins function by threading macromolecules through a central pore of a disc-shaped hexamer. Our results are consistent with a model in which Rca transiently threads the Rubisco large subunit N terminus through the axial pore of the AAA+ hexamer.
ISSN: 0021-9258
DOI: 10.1074/jbc.RA120.015759
Schools: School of Biological Sciences 
Rights: © 2020 Ng et al. Published under exclusive license by The American Society for Biochemistry and Molecular Biology, Inc. This is an Open Access article under the CC BY license.
Fulltext Permission: open
Fulltext Availability: With Fulltext
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