α-Glucan, water dikinase (GWD): A plastidic enzyme with redox-regulated and coordinated catalytic activity and binding affinity

Mikkelsen, René; Mutenda, Kudzai E.; Mant, Alexandra; Schürmann, Peter; Blennow, Andreas

doi:10.1073/pnas.0406674102

Cited by 129 publications

(123 citation statements)

References 43 publications

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“…First, enzymes shown to be regulated by Trx reside in the organelle, namely, ADP-glucose pyrophosphorylase (18), NADP-glucose 6-phosphate dehydrogenase (19,20), and ␣-glucan, water dikinase (21). Second, analyses of the constituent proteins (proteome) of amyloplasts have revealed the presence of a number of other enzymes that, in chloroplasts, are linked to Trx (refs.…”

Section: Resultsmentioning

confidence: 99%

A complete ferredoxin/thioredoxin system regulates fundamental processes in amyloplasts

Balmer

Vensel

Cai

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

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161

137

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A growing number of processes throughout biology are regulated by redox via thiol-disulfide exchange. This mechanism is particularly widespread in plants, where almost 200 proteins have been linked to thioredoxin (Trx), a widely distributed small regulatory disulfide protein. The current study extends regulation by Trx to amyloplasts, organelles prevalent in heterotrophic plant tissues that, among other biosynthetic activities, catalyze the synthesis and storage of copious amounts of starch. Using proteomics and immunological methods, we identified the components of the ferredoxin͞Trx system (ferredoxin, ferredoxin-Trx reductase, and Trx), originally described for chloroplasts, in amyloplasts isolated from wheat starchy endosperm. Ferredoxin is reduced not by light, as in chloroplasts, but by metabolically generated NADPH via ferredoxin-NADP reductase. However, once reduced, ferredoxin appears to act as established for chloroplasts, i.e., via ferredoxinTrx reductase and a Trx (m-type). A proteomics approach in combination with affinity chromatography and a fluorescent thiol probe led to the identification of 42 potential Trx target proteins, 13 not previously recognized, including a major membrane transporter (Brittle-1 or ADP-glucose transporter). The proteins function in a range of processes in addition to starch metabolism: biosynthesis of lipids, amino acids, and nucleotides; protein folding; and several miscellaneous reactions. The results suggest a mechanism whereby light is initially recognized as a thiol signal in chloroplasts, then as a sugar during transit to the sink, where it is converted again to a thiol signal. In this way, amyloplast reactions in the grain can be coordinated with photosynthesis taking place in leaves.redox regulation ͉ target proteins ͉ ferredoxin-thioredoxin reductase O ur understanding of the function of the regulatory disulfide protein thioredoxin (Trx) has increased dramatically in the past few years, with the advent of new methodologies. Recent approaches make it possible to identify proteins linked to Trx by combining proteomics with affinity chromatography (1) or thiol probes (2-4). These capabilities have defined an extended role of Trx in chloroplasts (1, 5) and helped elucidate its function in other plant systems: mitochondria (6), seeds (2,3,7,8), and seedlings (4, 9). Currently almost 200 proteins appear to be linked to Trx in plants (10). One major organelle that has been neglected, however, is the amyloplast, a plastid of heterotrophic tissues that performs a wide range of biosynthetic reactions, including the synthesis and storage of abundant quantities of starch.To help fill this gap, we have applied proteomic and immunological approaches to investigate the occurrence and function of Trx in amyloplasts. We now report evidence that amyloplasts isolated from wheat starchy endosperm resemble chloroplasts in containing a complete ferredoxin͞Trx system composed of ferredoxin, ferredoxin-Trx reductase (FTR), and Trx (m-type). Application of affinity chromatography and fl...

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Section: Resultsmentioning

confidence: 99%

A complete ferredoxin/thioredoxin system regulates fundamental processes in amyloplasts

Balmer

Vensel

Cai

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

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161

137

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“…The diurnal accumulation of starch thus seems to incorporate three regulatory elements: protein phosphorylation, redox, and pH. Redox is known to regulate other enzymes functional in starch metabolism, e.g., thioredoxin controls the activity of ADP-glucose pyrophosphorylase (18,19), the activity and binding of ␣-glucan, water dikinase (SEX1) to starch granules (20), and possibly the activity of ␤-amylase (21). However, to our knowledge, this is the first case in which redox has been linked to an enzyme involved with protein phosphorylation for the regulation of starch metabolism.…”

Section: Dsp4 Is a Major Phosphatase Associated With The Starch Granulementioning

confidence: 99%

A redox-regulated chloroplast protein phosphatase binds to starch diurnally and functions in its accumulation

Sokolov

Domı́nguez-Solı́s

Allary

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

108

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Starch is the ultimate storage molecule formed in the photosynthetic fixation of carbon dioxide by chloroplasts. Starch accumulates during the day and is degraded at night to intermediates that are exported to heterotrophic organs. The mechanism by which diurnal cycles control the transitory biosynthesis and degradation of chloroplast starch has long remained a mystery. We now report evidence that a dual-specificity protein phosphatase, DSP4, binds to starch granules during the day and dissociates at night. Disruption of the DSP4 gene resulted in a dramatic increase in the level of starch in mutant Arabidopsis plants. Moreover, although composition was apparently unchanged, the morphology of the starch granule was significantly altered compared to the wild type counterpart. Two regulatory factors linked to light (i.e., pH and redox status) changed both the activity and the starch-binding capacity of DSP4. The results further revealed that DSP4 represents a major fraction of granule-bound phosphatase activity during the day but not at night. Our study suggests that DSP4 acts as a bridge between light-induced redox changes and protein phosphorylation in the regulation of starch accumulation.redox regulation ͉ starch metabolism ͉ starch-binding phosphatase A s the ultimate storage form of photosynthetically fixed carbon, starch plays a central role in plants. During the day, chloroplasts convert carbon dioxide into soluble sugars that, with the collective action of starch synthases and branching enzymes, are converted to a mixture of linear and branched glucans (amylose and amylopectin) that determine the properties of the starch (1). At night, the starch granules are degraded by a combination of enzymes (2). The degradation products are transported out of the chloroplast and further exported to heterotrophic tissues in the form of sucrose (in most plants), thereby providing a carbon source for growth and energy. In this way, starch built up during the day and degraded at night meets the energy needs of the plant. The extent of starch synthesis and degradation in the chloroplast is tightly regulated by the lightdark cycle and by a number of environmental factors. However, little is known about the molecular mechanisms underlying the regulation of starch accumulation.Protein phosphorylation and dephosphorylation represents a ubiquitous mechanism for regulating cellular processes (3), including the enzymes of glycogen breakdown and synthesis. Furthermore, the protein kinases and phosphatases constituting the signaling pathways regulating these latter processes are now textbook material. By contrast, information on the regulation of starch metabolism by protein phosphorylation is scant.In an earlier effort to identify protein phosphatases in Arabidopsis that could dephosphorylate phosphotyrosine, we isolated both tyrosine-specific (4) and dual-specificity protein phosphatases (DSPs) (ref. 5 and L.N.S. and S.L., unpublished data) that may participate in a number of physiological and developmental processes (3). Several...

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“…15) Other GWDs also play an essential role in plastidial starch turn over in leaves as well as in potato tubers. 14,31,32) The debranching enzyme barley limit dextrinase. Barley limit dextrinase (LD), the key enzyme in α limit dextrin debranching and with high activity also on the linear polysaccharide pullulan, 18 21) has a major role in starch mobilization during seed germination and is possibly also involved in starch biosynthesis by trimming of intermediate branched α glucan structures.…”

mentioning

confidence: 99%

New Insight into Structure/Function Relationships in Plant .ALPHA.-Amylase Family GH13 Members

Seo¹,

Andersen²,

Nielsen³

et al. 2010

J. Appl. Glycosci.

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α-Glucan, water dikinase (GWD): A plastidic enzyme with redox-regulated and coordinated catalytic activity and binding affinity

Cited by 129 publications

References 43 publications

A complete ferredoxin/thioredoxin system regulates fundamental processes in amyloplasts

A complete ferredoxin/thioredoxin system regulates fundamental processes in amyloplasts

A redox-regulated chloroplast protein phosphatase binds to starch diurnally and functions in its accumulation

New Insight into Structure/Function Relationships in Plant .ALPHA.-Amylase Family GH13 Members

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