The role of the large subunit in redox regulation of the rice endosperm ADP‐glucose pyrophosphorylase. (30th September 2014)

• Record Type: Journal Article
• Authors: Tuncel, Aytug; Cakir, Bilal; Hwang, Seon‐Kap; Okita, Thomas W.
• Is Part Of: FEBS journal. Volume 281:Number 21(2014)
• Page Start: 4951
• Page End: 4963
• Publication Date: 2014-09-30
• Subjects: ADP‐glucose pyrophosphorylase -- allosteric regulation -- redox control -- rice endosperm -- starch; Biochemistry -- Periodicals; Molecular biology -- Periodicals; Pathology, Molecular -- Periodicals; 572
• DOI: 10.1111/febs.13041
• Languages: English
• ISSNs: 1742-464X

Abstract

Abstract : The starch regulatory enzyme ADP‐glucose pyrophosphorylase is activated by 3‐phosphoglyceric acid (3‐PGA) and inhibited by inorganic phosphate (Pi ). The activity of the plastid‐localized enzyme is also subject to fine regulation by redox control in response to changing light and sugar levels. The less active oxidized form of the enzyme contains an inter‐subunit disulfide bond formed between the pair of small subunit's Cys12 residues of the heterotetrameric enzyme. Although this cysteine residue is not conserved in the small subunits of cereal endosperm cytosolic AGPases, biochemical studies of the major rice endosperm enzyme indicate that the cytosolic isoform, like the plastidial enzymes, is subject to redox control. Kinetic analysis revealed that the reduced forms of the partially purified native and purified recombinant AGPases have 6‐ and 3.4‐fold, respectively, more affinity to 3‐PGA, rendering the enzymes more active at lower 3‐PGA concentration than the non‐reduced enzyme. Truncation of the large subunit by removal of N‐terminal peptide resulted in a decrease in 3‐PGA affinity and loss of redox response of the enzyme. Site‐directed mutagenesis of the conserved cysteine residues at the N‐terminal of the large subunit showed that C47 and C58, but not C12, are essential for proper redox response of the enzyme. Overall, our results show that the major rice endosperm AGPase activity is controlled by a combination of allosteric regulation and redox control, the latter through modification of the large subunit instead of the small subunit as evident in the plastid‐localized enzyme. Abstract : The major cytosolic isoform of the rice endosperm ADP‐glucose pyrophosphorylase is subject to redox regulation which occurs, unlike the leaf enzyme, through the large subunit of the heterotetrameric enzyme. The reduced forms of the native and recombinant enzymes have 3.4‐ to 6‐fold, more affinity to activator 3‐PGA. C47 and C58 residues of the large subunit are involved in redox control.