GDP-Mannose 3′,5′-Epimerase Forms GDP-L-gulose, a Putative Intermediate for the de Novo Biosynthesis of Vitamin C in Plants

Wolucka, Beata A.; Montagu, Marc Van

doi:10.1074/jbc.m309135200

Cited by 346 publications

(356 citation statements)

References 51 publications

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“…Pallanca and Smirnoff (24) have reported that the rate of AsA biosynthesis from D-[U- 14 C]glucose decreased linearly with the increase in the pool size of AsA in embryonic pea seedlings. In fact, L-Gal dehydrogenase and GME, which are in the D-Man/L-Gal pathway, were inhibited by AsA (9,25). These results suggest that the AsA level in plant cells is regulated at several steps by a feedback control.…”

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confidence: 63%

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Arabidopsis Phosphomannose Isomerase 1, but Not Phosphomannose Isomerase 2, Is Essential for Ascorbic Acid Biosynthesis

Maruta

Yonemitsu

Yabuta

et al. 2008

Journal of Biological Chemistry

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We studied molecular and functional properties of Arabidopsis phosphomannose isomerase isoenzymes (PMI1 and PMI2) that catalyze reversible isomerization between D-fructose 6-phosphate and D-mannose 6-phosphate (Man-6P). The apparent K m and V max values for Man-6P of purified recombinant PMI1 were 41.3 ؎ 4.2 M and 1.89 mol/min/mg protein, respectively, whereas those of purified recombinant PMI2 were 372 ؎ 13 M and 22.5 mol/min/mg protein, respectively. Both PMI1 and PMI2 were inhibited by incubation with EDTA, Zn 2؉ , Cd 2؉ , and L-ascorbic acid (AsA). Arabidopsis PMI1 protein was constitutively expressed in both vegetative and reproductive organs under normal growth conditions, whereas the PMI2 protein was not expressed in any organs under light. The induction of PMI1 expression and an increase in the AsA level were observed in leaves under continuous light, whereas the induction of PMI2 expression and a decrease in the AsA level were observed under long term darkness. PMI1 showed a diurnal expression pattern in parallel with the total PMI activity and the total AsA content in leaves. Moreover, a reduction of PMI1 expression through RNA interference resulted in a substantial decrease in the total AsA content of leaves of knockdown PMI1 plants, whereas the complete inhibition of PMI2 expression did not affect the total AsA levels in leaves of knock-out PMI2 plants. Consequently, this study improves our understanding of the molecular and functional properties of Arabidopsis PMI isoenzymes and provides genetic evidence of the involvement of PMI1, but not PMI2, in the biosynthesis of AsA in Arabidopsis plants.

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confidence: 63%

“…On incubation with 1 mM AsA, the GME of Arabidopsis plants was inhibited 15% (9). Recently, we have reported that L-Gal dehydrogenase activity was inhibited reversibly by AsA in a linearcompetitive manner (K i value of 133 M) (25).…”

Section: Discussionmentioning

confidence: 98%

Arabidopsis Phosphomannose Isomerase 1, but Not Phosphomannose Isomerase 2, Is Essential for Ascorbic Acid Biosynthesis

Maruta

Yonemitsu

Yabuta

et al. 2008

Journal of Biological Chemistry

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“…13 and this study), we found that VTC5 displays a strong substrate preference for GDP-L-Gal and GDP-D-Glc over GDP-L-Fuc and GDP-D-Man and that UDP-DGlc, UDP-D-Gal, and ADP-D-Glc are not substrates at all. Furthermore, as for VTC2, VTC5 does not seem to phosphorolyze GDP-L-gulose, a compound formed, in addition to GDP-L-Gal, from GDP-D-Man by GDP-D-mannose 3Ј,5Ј-epimerase (25) in the reaction catalyzed upstream of GDP-L-Gal phosphorolysis in the Smirnoff-Wheeler pathway. Neither VTC2 nor VTC5 does, thus, seem to participate in the putative vitamin C synthesis pathway involving L-gulose and L-gulono-1,4-lactone formation, one of the alternative pathways that has been proposed for vitamin C synthesis in plants (25).…”

Section: Discussionmentioning

confidence: 93%

“…Furthermore, as for VTC2, VTC5 does not seem to phosphorolyze GDP-L-gulose, a compound formed, in addition to GDP-L-Gal, from GDP-D-Man by GDP-D-mannose 3Ј,5Ј-epimerase (25) in the reaction catalyzed upstream of GDP-L-Gal phosphorolysis in the Smirnoff-Wheeler pathway. Neither VTC2 nor VTC5 does, thus, seem to participate in the putative vitamin C synthesis pathway involving L-gulose and L-gulono-1,4-lactone formation, one of the alternative pathways that has been proposed for vitamin C synthesis in plants (25). Both VTC2 and VTC5 catalyze the phosphorolysis of GDP-L-Gal and GDP-D-Glc much more efficiently than the corresponding reverse reactions.…”

Section: Discussionmentioning

confidence: 99%

A Second GDP-l-galactose Phosphorylase in Arabidopsis en Route to Vitamin C

Linster¹,

Adler²,

Webb³

et al. 2008

Journal of Biological Chemistry

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The Arabidopsis thaliana VTC2 gene encodes an enzyme that catalyzes the conversion of GDP-L-galactose to L-galactose 1-phosphate in the first committed step of the SmirnoffWheeler pathway to plant vitamin C synthesis. Mutations in VTC2 had previously been found to lead to only partial vitamin C deficiency. Here we show that the Arabidopsis gene At5g55120 encodes an enzyme with high sequence identity to VTC2. Designated VTC5, this enzyme displays substrate specificity and enzymatic properties that are remarkably similar to those of VTC2, suggesting that it may be responsible for residual vitamin C synthesis in vtc2 mutants. The exact nature of the reaction catalyzed by VTC2/VTC5 is controversial because of reports that kiwifruit and Arabidopsis VTC2 utilize hexose 1-phosphates as phosphorolytic acceptor substrates. Using liquid chromatography-mass spectroscopy and a VTC2-H238N mutant, we provide evidence that the reaction proceeds through a covalent guanylylated histidine residue within the histidine triad motif. Moreover, we show that both the Arabidopsis VTC2 and VTC5 enzymes catalyze simple phosphorolysis of the guanylylated enzyme, forming GDP and L-galactose 1-phosphate from GDP-L-galactose and phosphate, with poor reactivity of hexose 1-phosphates as phosphorolytic acceptors. Indeed, the endogenous activities from Japanese mustard spinach, lemon, and spinach have the same substrate requirements. These results show that Arabidopsis VTC2 and VTC5 proteins and their homologs in other plants are enzymes that guanylylate a conserved active site His residue with GDP-L-galactose, forming L-galactose 1-phosphate for vitamin C synthesis, and regenerate the enzyme with phosphate to form GDP.Vitamin C (L-ascorbic acid) is the most abundant soluble antioxidant in plants, in which it plays crucial roles in protection against oxidative damage and is used as a cofactor for several enzymes. It is synthesized via reactions initially proposed by Wheeler et al. (1) that are distinct from those used in vitamin C biosynthesis in animals. Although the Smirnoff-Wheeler pathway, arising from GDP-D-mannose and involving L-galactose formation, might not be the only route to vitamin C biosynthesis in plants (alternative pathways arising from myo-inositol and methylgalacturonate or involving L-gulose formation have been proposed; for reviews, see Refs. 2 and 3), it is undoubtedly the pathway that has received the strongest biochemical and genetic support in recent years (4 -9).Of the four loci (VTC1-4) that have been found to be mutated in vitamin C-deficient Arabidopsis thaliana plants (10, 11), three are now known to encode enzymes involved in the Smirnoff-Wheeler pathway. VTC1 encodes GDP-mannose pyrophosphorylase (12), whereasVTC4 encodes L-Gal-1-P 3 phosphatase (8). In 2007 the VTC2 gene product was identified as the enzyme that produces L-Gal-1-P from GDP-L-galactose, which completed the characterization of the 10 enzymatic steps leading from D-glucose to L-ascorbic acid (13,14). VTC2 is a member of the D-galactose-1-phosphate ...

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“…The biosynthesis of AsA proceeds via L-Gal (Wheeler et al, 1998), although conclusive evidence for all steps has only relatively recently become available (Conklin et al, 2006;Laing et al, 2007). Alternative biosynthetic routes involving uronic acids (Davey et al, 1999;Agius et al, 2003), L-gulose (Wolucka and Van Montagu, 2003), or myoinositol (Lorence et al, 2004) have been proposed in several plant species, including apple Razavi et al, 2005; Fig. 1), but their physiological relevance and contribution to the AsA pool is still far from clear in most plant species, with the possible exception of strawberry (Fragaria 3 ananassa; Agius et al, 2003;Cruz-Rus et al, 2011;Zorrilla-Fontanesi et al, 2011).…”

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confidence: 99%

Allelic Variation in Paralogs of GDP-l-Galactose Phosphorylase Is a Major Determinant of Vitamin C Concentrations in Apple Fruit

et al. 2012

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To identify the genetic factors underlying the regulation of fruit vitamin C (L-ascorbic acid [AsA]) concentrations, quantitative trait loci (QTL) studies were carried out in an F1 progeny derived from a cross between the apple (Malus 3 domestica) cultivars Telamon and Braeburn over three years. QTL were identified for AsA, glutathione, total antioxidant activity in both flesh and skin tissues, and various quality traits, including flesh browning. Four regions on chromosomes 10, 11, 16, and 17 contained stable fruit AsA-QTL clusters. Mapping of AsA metabolic genes identified colocations between orthologs of GDP-L-galactose phosphorylase (GGP), dehydroascorbate reductase (DHAR), and nucleobase-ascorbate transporter within these QTL clusters. Of particular interest are the three paralogs of MdGGP, which all colocated within AsA-QTL clusters. Allelic variants of MdGGP1 and MdGGP3 derived from the cultivar Braeburn parent were also consistently associated with higher fruit total AsA concentrations both within the mapping population (up to 10-fold) and across a range of commercial apple germplasm (up to 6-fold). Striking differences in the expression of the cv Braeburn MdGGP1 allele between fruit from high-and low-AsA genotypes clearly indicate a key role for MdGGP1 in the regulation of fruit AsA concentrations, and this MdGGP allele-specific single-nucleotide polymorphism marker represents an excellent candidate for directed breeding for enhanced fruit AsA concentrations. Interestingly, colocations were also found between MdDHAR3-3 and a stable QTL for browning in the cv Telamon parent, highlighting links between the redox status of the AsA pool and susceptibility to flesh browning.

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GDP-Mannose 3′,5′-Epimerase Forms GDP-L-gulose, a Putative Intermediate for the de Novo Biosynthesis of Vitamin C in Plants

Cited by 346 publications

References 51 publications

Arabidopsis Phosphomannose Isomerase 1, but Not Phosphomannose Isomerase 2, Is Essential for Ascorbic Acid Biosynthesis

Arabidopsis Phosphomannose Isomerase 1, but Not Phosphomannose Isomerase 2, Is Essential for Ascorbic Acid Biosynthesis

A Second GDP-l-galactose Phosphorylase in Arabidopsis en Route to Vitamin C

Allelic Variation in Paralogs of GDP-l-Galactose Phosphorylase Is a Major Determinant of Vitamin C Concentrations in Apple Fruit

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