Journal Article

Redox modulation of Rubisco conformation and activity through its cysteine residues

Joaquín Moreno, María Jesús García-Murria and Julia Marín-Navarro

in Journal of Experimental Botany

Published on behalf of Society for Experimental Biology

Volume 59, issue 7, pages 1605-1614
Published in print May 2008 | ISSN: 0022-0957
Published online January 2008 | e-ISSN: 1460-2431 | DOI: http://dx.doi.org/10.1093/jxb/erm310
Redox modulation of Rubisco conformation and activity through its cysteine residues

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Treatment of purified Rubisco with agents that specifically oxidize cysteine-thiol groups causes catalytic inactivation and increased proteolytic sensitivity of the enzyme. It has been suggested that these redox properties may sustain a mechanism of regulating Rubisco activity and turnover during senescence or stress. Current research efforts are addressing the structural basis of the redox modulation of Rubisco and the identification of critical cysteines. Redox shifts result in Rubisco conformational changes as revealed by the alteration of its proteolytic fragmentation pattern upon oxidation. In particular, the augmented susceptibility of Rubisco to proteases is due to increased exposure of a small loop (between Ser61 and Thr68) when oxidized. Progressive oxidation of Rubisco cysteines using disulphide/thiol mixtures at different ratios have shown that inactivation occurs under milder oxidative conditions than proteolytic sensitization, suggesting the involvement of different critical cysteines. Site-directed mutagenesis of conserved cysteines in the Chlamydomonas reinhardtii Rubisco identified Cys449 and Cys459 among those involved in oxidative inactivation, and Cys172 and Cys192 as the specific target for arsenite. The physiological importance of Rubisco redox regulation is supported by the in vivo response of the cysteine mutants to stress conditions. Substitution of Cys172 caused a pronounced delay in stress-induced Rubisco degradation, while the replacement of the functionally redundant Cys449-Cys459 pair resulted in an enhanced catabolism with a faster high-molecular weight polymerization and translocation to membranes. These results suggest that several cysteines contribute to a sequence of conformational changes that trigger the different stages of Rubisco catabolism under increasing oxidative conditions.

Keywords: Chlamydomonas reinhardtii; chloroplast; critical cysteines; oxidative inactivation; proteolytic enhancement; redox control; Rubisco catabolism; senescence; site-directed mutants; thiol-disulphide exchange

Journal Article.  5997 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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