Journal Article

Inter-species variation in the oligomeric states of the higher plant Calvin cycle enzymes glyceraldehyde-3-phosphate dehydrogenase and phosphoribulokinase

Thomas P. Howard, Julie C. Lloyd and Christine A. Raines

in Journal of Experimental Botany

Published on behalf of Society for Experimental Biology

Volume 62, issue 11, pages 3799-3805
Published in print July 2011 | ISSN: 0022-0957
Published online April 2011 | e-ISSN: 1460-2431 | DOI: http://dx.doi.org/10.1093/jxb/err057

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In darkened leaves the Calvin cycle enzymes glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and phosphoribulokinase (PRK) form a regulatory multi-enzyme complex with the small chloroplast protein CP12. GAPDH also forms a high molecular weight regulatory mono-enzyme complex. Given that there are different reports as to the number and subunit composition of these complexes and that enzyme regulatory mechanisms are known to vary between species, it was reasoned that protein–protein interactions may also vary between species. Here, this variation is investigated. This study shows that two different tetramers of GAPDH (an A2B2 heterotetramer and an A4 homotetramer) have the capacity to form part of the PRK/GAPDH/CP12 complex. The role of the PRK/GAPDH/CP12 complex is not simply to regulate the ‘non-regulatory’ A4 GAPDH tetramer. This study also demonstrates that the abundance and nature of PRK/GAPDH/CP12 interactions are not equal in all species and that whilst NAD enhances complex formation in some species, this is not sufficient for complex formation in others. Furthermore, it is shown that the GAPDH mono-enzyme complex is more abundant as a 2(A2B2) complex, rather than the larger 4(A2B2) complex. This smaller complex is sensitive to cellular metabolites indicating that it is an important regulatory isoform of GAPDH. This comparative study has highlighted considerable heterogeneity in PRK and GAPDH protein interactions between closely related species and the possible underlying physiological basis for this is discussed.

Keywords: Blue native PAGE; Calvin cycle; CP12; glyceraldehyde-3-phosphate dehydrogenase (GAPDH); phosphoribulokinase (PRK); protein–protein interactions

Journal Article.  4347 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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