Thioredoxin-dependent regulation of photosynthetic glyceraldehyde-3-phosphate dehydrogenase: autonomous vs. CP12-dependent mechanisms.

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Trost P, Fermani S, Marri L, Zaffagnini M, Falini G, Scagliarini S, Pupillo P, Sparla F

Thioredoxin-dependent regulation of photosynthetic glyceraldehyde-3-phosphate dehydrogenase: autonomous vs. CP12-dependent mechanisms.

Photosynth Res. 2006 Sep;89(2-3):263-75. Epub 2006 Sep 22.

PubMed ID

17031544 [ View in PubMed

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Abstract

Regulation of the Calvin-Benson cycle under varying light/dark conditions is a common property of oxygenic photosynthetic organisms and photosynthetic glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is one of the targets of this complex regulatory system. In cyanobacteria and most algae, photosynthetic GAPDH is a homotetramer of GapA subunits which do not contain regulatory domains. In these organisms, dark-inhibition of the Calvin-Benson cycle involves the formation of a kinetically inhibited supramolecular complex between GAPDH, the regulatory peptide CP12 and phosphoribulokinase. Conditions prevailing in the dark, i.e. oxidation of thioredoxins and low NADP(H)/NAD(H) ratio promote aggregation. Although this regulatory system has been inherited in higher plants, these phototrophs contain in addition a second type of GAPDH subunits (GapB) resulting from the fusion of GapA with the C-terminal half of CP12. Heterotetrameric A(2)B(2)-GAPDH constitutes the major photosynthetic GAPDH isoform of higher plants chloroplasts and coexists with CP12 and A(4)-GAPDH. GapB subunits of A(2)B(2)-GAPDH have inherited from CP12 a regulatory domain (CTE for C-terminal extension) which makes the enzyme sensitive to thioredoxins and pyridine nucleotides, resembling the GAPDH/CP12/PRK system. The two systems are similar in other respects: oxidizing conditions and low NADP(H)/NAD(H) ratios promote aggregation of A(2)B(2)-GAPDH into strongly inactivated A(8)B(8)-GAPDH hexadecamers, and both CP12 and CTE specifically affect the NADPH-dependent activity of GAPDH. The alternative, lower activity with NADH is always unaffected. Based on the crystal structure of spinach A(4)-GAPDH and the analysis of site-specific mutants, a model of the autonomous (CP12-independent) regulatory mechanism of A(2)B(2)-GAPDH is proposed. Both CP12 and CTE seem to regulate different photosynthetic GAPDH isoforms according to a common and ancient molecular mechanism.

DrugBank Data that Cites this Article

Drug Targets

Drug	Target	Kind	Organism	Pharmacological Action	Actions
NADH	Glyceraldehyde-3-phosphate dehydrogenase	Protein	Humans	Unknown	Not Available	Details