Dataset Information

Enantioselective induction of a glutathione-S-transferase, a glutathione transporter and an ABC transporter in maize by Metolachlor and its (S)-isomer.

ABSTRACT: The metabolism of chiral herbicides in plants remains poorly understood. Glutathione conjugation reactions are one of the principal mechanisms that plants utilize to detoxify xenobiotics. The induction by rac- and S-metolachlor of the expression of three genes, ZmGST27, ZmGT1 and ZmMRP1, encoding respectively a glutathione-S-transferase, a glutathione transporter and an ATP-binding cassette (ABC) transporter was studied in maize. The results demonstrate that the inducing effect of rac- and S-metolachlor on the expression of ZmGST27 and ZmGT1 is comparable. However, the inducing effect of rac-metolachlor on ZmMRP1 expression is more pronounced than that of S-metolachlor. Furthermore, vanadate, an ABC transporter inhibitor, could greatly reduce the difference in herbicidal activity between rac- and S-metolachlor. These results suggest that the ABC transporters may preferentially transport conjugates of rac-metolachlor, leading to a faster metabolism of the latter. Through comparing the expression of ZmGST27, ZmMRP1 and ZmGT1 after treatment by rac- and S-metolachlor, we provide novel insights into the metabolic processes of chiral herbicides in plants.

SUBMITTER: Pang S

PROVIDER: S-EPMC3483294 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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Publications

Enantioselective induction of a glutathione-S-transferase, a glutathione transporter and an ABC transporter in maize by Metolachlor and its (S)-isomer.

Pang Sen S Ran Zhaojin Z Liu Zhiqian Z Song Xiaoyu X Duan Liusheng L Li Xuefeng X Wang Chengju C

PloS one 20121029 10

The metabolism of chiral herbicides in plants remains poorly understood. Glutathione conjugation reactions are one of the principal mechanisms that plants utilize to detoxify xenobiotics. The induction by rac- and S-metolachlor of the expression of three genes, ZmGST27, ZmGT1 and ZmMRP1, encoding respectively a glutathione-S-transferase, a glutathione transporter and an ATP-binding cassette (ABC) transporter was studied in maize. The results demonstrate that the inducing effect of rac- and S-met ...[more]

PMID: 23144728

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Project description:The isoenzyme glutathione S-transferase (GST) I from maize (Zea mays) was cloned and expressed in Escherichia coli, and its catalytic mechanism was investigated by site-directed mutagenesis and dynamic studies. The results showed that the enzyme promotes proton dissociation from the GSH thiol and creates a thiolate anion with high nucleophilic reactivity by lowering the pK(a) of the thiol from 8.7 to 6.2. Steady-state kinetics fit well to a rapid equilibrium, random sequential Bi Bi mechanism, with intrasubunit modulation between the GSH binding site (G-site) and the electrophile binding site (H-site). The rate-limiting step of the reaction is viscosity-dependent, and thermodynamic data suggest that product release is rate-limiting. Five residues of GST I (Ser(11), His(40), Lys(41), Gln(53) and Ser(67)), which are located in the G-site, were individually replaced with alanine and their structural and functional roles in the 1-chloro-2,4-dinitrobenzene (CDNB) conjugation reaction were investigated. On the basis of steady-state kinetics, difference spectroscopy and limited proteolysis studies it is concluded that these residues: (1) contribute to the affinity of the G-site for GSH, as they are involved in side-chain interaction with GSH; (2) influence GSH thiol ionization, and thus its reactivity; (3) participate in k(cat) regulation by affecting the rate-limiting step of the reaction; and (4) in the cases of His(40), Lys(41) and Gln(53) play an important role in the structural integrity of, and probably in the flexibility of, the highly mobile short 3(10)-helical segment of alpha-helix 2 (residues 35-46), as shown by limited proteolysis experiments. These structural perturbations are probably transmitted to the H-site through changes in Phe(35) conformation. This accounts for the modulation of K(CDNB)(m) by His(40), Lys(41) and Gln(53), and also for the intrasubunit communication between the G- and H-sites. Computer simulations using CONCOORD were applied to maize GST I monomer and dimer structures, each with bound lactoylglutathione, and the results were analysed by the essential dynamics technique. Differences in dynamics were found between the monomer and the dimer simulations showing the importance of using the whole structure in dynamic analysis. The results obtained confirm that the short 3(10)-helical segment of alpha-helix 2 (residues 35-46) undergoes the most significant structural rearrangements. These rearrangements are discussed in terms of enzyme catalytic mechanism.

Dataset Information

Enantioselective induction of a glutathione-S-transferase, a glutathione transporter and an ABC transporter in maize by Metolachlor and its (S)-isomer.

Publications

Enantioselective induction of a glutathione-S-transferase, a glutathione transporter and an ABC transporter in maize by Metolachlor and its (S)-isomer.

Similar Datasets

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