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Tzafestas K, Ahmad L, Dani MP, Grogan G, Rylott EL, Bruce NC. Structure-Guided Mechanisms Behind the Metabolism of 2,4,6-Trinitrotoluene by Glutathione Transferases U25 and U24 That Lead to Alternate Product Distribution. Front Plant Sci 2018; 9:1846. [PMID: 30631331 PMCID: PMC6315187 DOI: 10.3389/fpls.2018.01846] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/14/2018] [Accepted: 11/28/2018] [Indexed: 06/09/2023]
Abstract
The explosive xenobiotic 2,4,6-trinitrotoluene (TNT) is a major worldwide environmental pollutant and its persistence in the environment presents health and environmental concerns. The chemical structure of TNT dictates that biological detoxification pathways follow predominantly reductive transformation of the nitro groups, and as a result, TNT is notoriously recalcitrant to mineralization in the environment. Plant-based technologies to remediate this toxic pollutant rely on a solid understanding of the biochemical detoxification pathways involved. Toward this, two Arabidopsis Tau class glutathione transferases, GSTU24 and GSTU25, have been identified that catalyze the formation of three TNT-glutathionylated conjugates. These two GSTs share 79% identity yet only GSTU25 catalyzes the substitution of a nitro group for sulfur to form 2-glutathionyl-4,6-dinitrotoluene. The production of this compound is of interest because substitution of a nitro group could lead to destabilization of the aromatic ring, enabling subsequent biodegradation. To identify target amino acids within GSTU25 that might be involved in the formation of 2-glutathionyl-4,6-dinitrotoluene, the structure for GSTU25 was determined, in complex with oxidized glutathione, and used to inform site-directed mutagenesis studies. Replacement of five amino acids in GSTU24 established a conjugate profile and activity similar to that found in GSTU25. These findings contribute to the development of plant-based remediation strategies for the detoxification of TNT in the environment.
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Affiliation(s)
- Kyriakos Tzafestas
- Centre for Novel Agricultural Products, Department of Biology, University of York, York, United Kingdom
| | - Laziana Ahmad
- Centre for Novel Agricultural Products, Department of Biology, University of York, York, United Kingdom
- York Structural Biology Laboratory, Department of Chemistry, University of York, York, United Kingdom
| | - M. Paulina Dani
- Centre for Novel Agricultural Products, Department of Biology, University of York, York, United Kingdom
| | - Gideon Grogan
- York Structural Biology Laboratory, Department of Chemistry, University of York, York, United Kingdom
| | - Elizabeth L. Rylott
- Centre for Novel Agricultural Products, Department of Biology, University of York, York, United Kingdom
| | - Neil C. Bruce
- Centre for Novel Agricultural Products, Department of Biology, University of York, York, United Kingdom
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Tzafestas K, Razalan MM, Gyulev I, Mazari AMA, Mannervik B, Rylott EL, Bruce NC. Expression of a Drosophila glutathione transferase in Arabidopsis confers the ability to detoxify the environmental pollutant, and explosive, 2,4,6-trinitrotoluene. New Phytol 2017; 214:294-303. [PMID: 27924627 DOI: 10.1111/nph.14326] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2016] [Accepted: 10/09/2016] [Indexed: 06/06/2023]
Abstract
The explosive 2,4,6-trinitrotoluene (TNT) is a significant, global environmental pollutant that is both toxic and recalcitrant to degradation. Given the sheer scale and inaccessible nature of contaminated areas, phytoremediation may be a viable clean-up approach. Here, we have characterized a Drosophila melanogaster glutathione transferase (DmGSTE6) which has activity towards TNT. Recombinantly expressed, purified DmGSTE6 produces predominantly 2-glutathionyl-4,6-dinitrotoluene, and has a 2.5-fold higher Maximal Velocity (Vmax ), and five-fold lower Michaelis Constant (Km ) than previously characterized TNT-active Arabidopsis thaliana (Arabidopsis) GSTs. Expression of DmGSTE6 in Arabidopsis conferred enhanced resistance to TNT, and increased the ability to remove TNT from contaminated soil relative to wild-type plants. Arabidopsis lines overexpressing TNT-active GSTs AtGST-U24 and AtGST-U25 were compromised in biomass production when grown in the absence of TNT. This yield drag was not observed in the DmGSTE6-expressing Arabidopsis lines. We hypothesize that increased levels of endogenous TNT-active GSTs catalyse excessive glutathionylation of endogenous substrates, depleting glutathione pools, an activity that DmGST may lack. In conclusion, DmGSTE6 has activity towards TNT, producing a compound with potential for further biodegradation. Selecting or manipulating plants to confer DmGSTE6-like activity could contribute towards development of phytoremediation strategies to clean up TNT from polluted military sites.
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Affiliation(s)
- Kyriakos Tzafestas
- Centre for Novel Agricultural Products, Department of Biology, University of York, York, YO10 5DD, UK
| | - Maria M Razalan
- Centre for Novel Agricultural Products, Department of Biology, University of York, York, YO10 5DD, UK
| | - Ivan Gyulev
- Centre for Novel Agricultural Products, Department of Biology, University of York, York, YO10 5DD, UK
| | - Aslam M A Mazari
- Department of Neurochemistry, Stockholm University, S-106 91, Stockholm, Sweden
| | - Bengt Mannervik
- Department of Neurochemistry, Stockholm University, S-106 91, Stockholm, Sweden
| | - Elizabeth L Rylott
- Centre for Novel Agricultural Products, Department of Biology, University of York, York, YO10 5DD, UK
| | - Neil C Bruce
- Centre for Novel Agricultural Products, Department of Biology, University of York, York, YO10 5DD, UK
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Rylott EL, Gunning V, Tzafestas K, Sparrow H, Johnston EJ, Brentnall AS, Potts JR, Bruce NC. Phytodetoxification of the environmental pollutant and explosive 2,4,6-trinitrotoluene. Plant Signal Behav 2015; 10:e977714. [PMID: 25654165 PMCID: PMC5154393 DOI: 10.4161/15592324.2014.977714] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Our recent study highlights the role of 2 glutathione transferases (GSTs) in the detoxification of the environmental pollutant, 2,4,6-trinitrotoluene (TNT) in Arabidopsis thaliana. TNT is toxic and highly resistant to biodegradation in the environment, raising both health and environmental concerns. Two GSTs, GST-U24 and GST-U25, are upregulated in response to TNT treatment, and expressed predominantly in the root tissues; the site of TNT location following uptake. Plants overexpressing GST-U24 and GST-U25 exhibited significantly enhanced ability to withstand and detoxify TNT, and remove TNT from contaminated soil. Analysis of the catalytic activities of these 2 enzymes revealed that they form 3 TNT-glutathionyl products. Of particular interest is 2-glutathionyl-4,6-dinitrotoluene as this represents a potentially favorable step toward subsequent degradation and mineralization of TNT. We demonstrate how GSTs fit into what is already known about pathways for TNT detoxification, and discuss the short and longer-term fate of TNT conjugates in planta.
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Affiliation(s)
- Elizabeth L Rylott
- Centre for Novel Agricultural Products;
Department of Biology; University of York; York,
UK
- Correspondence to: Elizabeth L Rylott;
| | - Vanda Gunning
- Centre for Novel Agricultural Products;
Department of Biology; University of York; York,
UK
| | - Kyriakos Tzafestas
- Centre for Novel Agricultural Products;
Department of Biology; University of York; York,
UK
| | - Helen Sparrow
- Centre for Novel Agricultural Products;
Department of Biology; University of York; York,
UK
| | - Emily J Johnston
- Centre for Novel Agricultural Products;
Department of Biology; University of York; York,
UK
| | | | | | - Neil C Bruce
- Centre for Novel Agricultural Products;
Department of Biology; University of York; York,
UK
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Gunning V, Tzafestas K, Sparrow H, Johnston EJ, Brentnall AS, Potts JR, Rylott EL, Bruce NC. Arabidopsis Glutathione Transferases U24 and U25 Exhibit a Range of Detoxification Activities with the Environmental Pollutant and Explosive, 2,4,6-Trinitrotoluene. Plant Physiol 2014; 165:854-865. [PMID: 24733884 PMCID: PMC4044842 DOI: 10.1104/pp.114.237180] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
The explosive 2,4,6-trinitrotoluene (TNT) is a major worldwide military pollutant. The presence of this toxic and highly persistent pollutant, particularly at military sites and former manufacturing facilities, presents various health and environmental concerns. Due to the chemically resistant structure of TNT, it has proven to be highly recalcitrant to biodegradation in the environment. Here, we demonstrate the importance of two glutathione transferases (GSTs), GST-U24 and GST-U25, from Arabidopsis (Arabidopsis thaliana) that are specifically up-regulated in response to TNT exposure. To assess the role of GST-U24 and GST-U25, we purified and characterized recombinant forms of both enzymes and demonstrated the formation of three TNT glutathionyl products. Importantly, GST-U25 catalyzed the denitration of TNT to form 2-glutathionyl-4,6-dinitrotoluene, a product that is likely to be more amenable to subsequent biodegradation in the environment. Despite the presence of this biochemical detoxification pathway in plants, physiological concentrations of GST-U24 and GST-U25 result in only a limited innate ability to cope with the levels of TNT found at contaminated sites. We demonstrate that Arabidopsis plants overexpressing GST-U24 and GST-U25 exhibit significantly enhanced ability to withstand and detoxify TNT, properties that could be applied for in planta detoxification of TNT in the field. The overexpressing lines removed significantly more TNT from soil and exhibited a corresponding reduction in glutathione levels when compared with wild-type plants. However, in the absence of TNT, overexpression of these GSTs reduces root and shoot biomass, and although glutathione levels are not affected, this effect has implications for xenobiotic detoxification.
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Affiliation(s)
- Vanda Gunning
- Centre for Novel Agricultural Products (V.G., K.T., H.S., E.J.J., E.L.R., N.C.B.) and Department of Biology (A.S.B., J.R.P.), University of York, York YO10 5DD, United Kingdom
| | - Kyriakos Tzafestas
- Centre for Novel Agricultural Products (V.G., K.T., H.S., E.J.J., E.L.R., N.C.B.) and Department of Biology (A.S.B., J.R.P.), University of York, York YO10 5DD, United Kingdom
| | - Helen Sparrow
- Centre for Novel Agricultural Products (V.G., K.T., H.S., E.J.J., E.L.R., N.C.B.) and Department of Biology (A.S.B., J.R.P.), University of York, York YO10 5DD, United Kingdom
| | - Emily J Johnston
- Centre for Novel Agricultural Products (V.G., K.T., H.S., E.J.J., E.L.R., N.C.B.) and Department of Biology (A.S.B., J.R.P.), University of York, York YO10 5DD, United Kingdom
| | - Andrew S Brentnall
- Centre for Novel Agricultural Products (V.G., K.T., H.S., E.J.J., E.L.R., N.C.B.) and Department of Biology (A.S.B., J.R.P.), University of York, York YO10 5DD, United Kingdom
| | - Jennifer R Potts
- Centre for Novel Agricultural Products (V.G., K.T., H.S., E.J.J., E.L.R., N.C.B.) and Department of Biology (A.S.B., J.R.P.), University of York, York YO10 5DD, United Kingdom
| | - Elizabeth L Rylott
- Centre for Novel Agricultural Products (V.G., K.T., H.S., E.J.J., E.L.R., N.C.B.) and Department of Biology (A.S.B., J.R.P.), University of York, York YO10 5DD, United Kingdom
| | - Neil C Bruce
- Centre for Novel Agricultural Products (V.G., K.T., H.S., E.J.J., E.L.R., N.C.B.) and Department of Biology (A.S.B., J.R.P.), University of York, York YO10 5DD, United Kingdom
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