Small Oligomers of Ribulose-bisphosphate Carboxylase/Oxygenase (Rubisco) Activase Are Required for Biological Activity

Ribulose bisphosphate carboxylase/oxygenase (Rubisco), an abundant enzyme in chloroplasts, must be activated by CO2 in order for it to catalyze the carboxylation of ribulose bisphosphate. Rubisco activase, a nuclear encoded chloroplast protein was first identified as a biochemical lesion in the rca mutant of Arabidopsis (1) which lacked this enzyme. Study of Rubisco in this mutant (2) and transgenic tobacco plants with reduced Rubisco activase levels showed that Rubisco could not achieve and maintain an adequate level of activity, in vivo, without an activase. Rubisco activase promotes ‘activation’ of Rubisco by overcoming the deleterious effects of tight binding sugar phosphates and low chloroplast CO2 levels on catalysis and carbamylation (1).Rubisco activase has been detected in higher plants (3), in unicellular green algae (4,5) and in cyanobacteria (6). Though the presence of Rubisco in guard cell chlroplasts was a subject of controversy, several immunolight and immunoelectron microscopic studies have demonstrated the presence of Rubisco in guard cells (7).

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Atomic Resolution X-ray Structure of the Substrate Recognition Domain of Higher Plant Ribulose-bisphosphate Carboxylase/Oxygenase (Rubisco) Activase

Journal of Biological Chemistry ◽

10.1074/jbc.c111.289595 ◽

2011 ◽

Vol 286 (41) ◽

pp. 35683-35688 ◽

Cited By ~ 26

Author(s):

J. Nathan Henderson ◽

Agnieszka M. Kuriata ◽

Raimund Fromme ◽

Michael E. Salvucci ◽

Rebekka M. Wachter

Keyword(s):

Mechanical Energy ◽

Tight Binding ◽

Rubisco Activase ◽

Ribulose Bisphosphate Carboxylase ◽

Ribulose Bisphosphate ◽

Higher Plant ◽

Bisphosphate Carboxylase ◽

Aaa Atpase ◽

Ribulose Bisphosphate Carboxylase Oxygenase ◽

Species Specific

The rapid release of tight-binding inhibitors from dead-end ribulose-bisphosphate carboxylase/oxygenase (Rubisco) complexes requires the activity of Rubisco activase, an AAA+ ATPase that utilizes chemo-mechanical energy to catalyze the reactivation of Rubisco. Activase is thought to play a central role in coordinating the rate of CO2 fixation with the light reactions of photosynthesis. Here, we present a 1.9 Å crystal structure of the C-domain core of creosote activase. The fold consists of a canonical four-helix bundle, from which a paddle-like extension protrudes that entails a nine-turn helix lined by an irregularly structured peptide strand. The residues Lys-313 and Val-316 involved in the species-specific recognition of Rubisco are located near the tip of the paddle. An ionic bond between Lys-313 and Glu-309 appears to stabilize the glycine-rich end of the helix. Structural superpositions onto the distant homolog FtsH imply that the paddles extend away from the hexameric toroid in a fan-like fashion, such that the hydrophobic sides of each blade bearing Trp-302 are facing inward and the polar sides bearing Lys-313 and Val-316 are facing outward. Therefore, we speculate that upon binding, the activase paddles embrace the Rubisco cylinder by placing their hydrophobic patches near the partner protein. This model suggests that conformational adjustments at the remote end of the paddle may relate to selectivity in recognition, rather than specific ionic contacts involving Lys-313. Additionally, the superpositions predict that the catalytically critical Arg-293 does not interact with the bound nucleotide. Hypothetical ring-ring stacking and peptide threading models for Rubisco reactivation are briefly discussed.

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