Phytochelatin synthase catalyzes key step in turnover of glutathione conjugates

Beck, Andreas; Lendzian, Klaus J.; Oven, Matjaž; Christmann, Alexander; Grill, Erwin

doi:10.1016/s0031-9422(02)00565-4

Cited by 62 publications

(75 citation statements)

References 20 publications

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“…This would require that GSH is first converted to phytochelatins by phytochelatin synthase before GGC removes the N-terminal g-glutamyl group to make 5OP. Recently, the cytosolic hydrolysis of GSH conjugates to g-EC conjugates by phytochelatin synthase was reported (Beck et al, 2003;Blum et al, 2007). Since phytochelatin synthase requires a heavy metal, this does not seem likely to be important in our in vitro GGC assay.…”

Section: Discussionmentioning

confidence: 96%

Aγ-Glutamyl Transpeptidase-Independent Pathway of Glutathione Catabolism to Glutamate via 5-Oxoproline in Arabidopsis

et al. 2008

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The degradation pathway of glutathione (GSH) in plants is not well understood. In mammals, GSH is predominantly metabolized through the g-glutamyl cycle, where GSH is degraded by the sequential reaction of g-glutamyl transpeptidase (GGT), g-glutamyl cyclotransferase, and 5-oxoprolinase to yield glutamate (Glu) and dipeptides that are subject to peptidase action. In this study, we examined if GSH is degraded through the same pathway in Arabidopsis (Arabidopsis thaliana) as occurs in mammals. In Arabidopsis, the oxoprolinase knockout mutants (oxp1-1 and oxp1-2) accumulate more 5-oxoproline (5OP) and less Glu than wild-type plants, suggesting substantial metabolite flux though 5OP and that 5OP is a major contributor to Glu steady-state levels. In the ggt1-1/ggt4-1/oxp1-1 triple mutant with no GGT activity in any organs except young siliques, the 5OP concentration in leaves was not different from that in oxp1-1, suggesting that GGTs are not major contributors to 5OP production in Arabidopsis. 5OP formation strongly tracked the level of GSH in Arabidopsis plants, suggesting that GSH is the precursor of 5OP in a GGT-independent reaction. Kinetics analysis suggests that g-glutamyl cyclotransferase is the major source of GSH degradation and 5OP formation in Arabidopsis. This discovery led us to propose a new pathway for GSH turnover in plants where GSH is converted to 5OP and then to Glu by the combined action of g-glutamyl cyclotransferase and 5-oxoprolinase in the cytoplasm.

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Section: Discussionmentioning

confidence: 96%

Aγ-Glutamyl Transpeptidase-Independent Pathway of Glutathione Catabolism to Glutamate via 5-Oxoproline in Arabidopsis

et al. 2008

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“…One mode is that the initial step is the removal of the Glu residue from the N terminus catalyzed by g-glutamyl transpeptidases, for example, GGTs in Arabidopsis (Ohkama-Ohtsu et al, 2007a, 2007b. The other mode is that the initial step is the removal of the Gly residue from the C terminus catalyzed by PCS, for example, PCSs in Arabidopsis (Beck et al, 2003). Both MKK9-and B. cinerea-induced camalexin …”

Section: Both Mkk9 Activation and B Cinerea Infection Led To Accumulmentioning

confidence: 99%

Glutathione-Indole-3-Acetonitrile Is Required for Camalexin Biosynthesis in Arabidopsis thaliana

et al. 2011

The Plant Cell

116

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Camalexin, a major phytoalexin in Arabidopsis thaliana, consists of an indole ring and a thiazole ring. The indole ring is produced from Trp, which is converted to indole-3-acetonitrile (IAN) by CYP79B2/CYP79B3 and CYP71A13. Conversion of Cys(IAN) to dihydrocamalexic acid and subsequently to camalexin is catalyzed by CYP71B15. Recent studies proposed that Cys derivative, not Cys itself, is the precursor of the thiazole ring that conjugates with IAN. The nature of the Cys derivative and how it conjugates to IAN and subsequently forms Cys(IAN) remain obscure. We found that protein accumulation of multiple glutathione S-transferases (GSTs), elevation of GST activity, and consumption of glutathione (GSH) coincided with camalexin production. GSTF6 overexpression increased and GSTF6-knockout reduced camalexin production. Arabidopsis GSTF6 expressed in yeast cells catalyzed GSH(IAN) formation. GSH(IAN), (IAN)CysGly, and gGluCys(IAN) were determined to be intermediates within the camalexin biosynthetic pathway. Inhibitor treatments and mutant analyses revealed the involvement of g-glutamyl transpeptidases (GGTs) and phytochelatin synthase (PCS) in the catabolism of GSH(IAN). The expression of GSTF6, GGT1, GGT2, and PCS1 was coordinately upregulated during camalexin biosynthesis. These results suggest that GSH is the Cys derivative used during camalexin biosynthesis, that the conjugation of GSH with IAN is catalyzed by GSTF6, and that GGTs and PCS are involved in camalexin biosynthesis.

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“…One possibility, other than PC synthesis per se, is that the bacterial enzymes serve to cleave glutathione S-conjugates (GS-conjugates). Knowing that GS-conjugate cleavage is a major auxiliary capability of eukaryotic PC synthases (Beck et al, 2003;Vatamaniuk et al, 2004) and that glutathione S-transferases (GSTs) and/or their homologs are represented in the genomes of all of the bacteria possessing PC synthase homologs hints at the possibility that bacterial PC synthase homologs participate in GS-conjugate degradation. Pathways for the processing of bacterial GS-conjugates entailing the same deglycylation reaction as that catalyzed by eukaryotic PC synthases (Beck et al, 2003;Vatamaniuk et al, 2004) and proposed to function in the detoxification of GS-conjugable xenobiotics in plants (Beck et al, 2003) might be envisaged.…”

Section: Pc Synthase Is a Cys Transpeptidasementioning

confidence: 99%