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Title: Novosphingobium aromaticivorans uses a Nu-class glutathione S -transferase as a glutathione lyase in breaking the β-aryl ether bond of lignin

As a major component of plant cells walls, lignin is a potential renewable source of valuable chemicals. Several sphingomonad bacteria have been identified that can break the β-aryl ether bond connecting most phenylpropanoid units of the lignin heteropolymer. Here, we tested three sphingomonads predicted to be capable of breaking the β-aryl ether bond of the dimeric aromatic compound guaiacylglycerol-β-guaiacyl ether (GGE) and found that Novosphingobium aromaticivorans metabolizes GGE at one of the fastest rates thus far reported. After the ether bond of racemic GGE is broken by replacement with a thioether bond involving glutathione, the glutathione moiety must be removed from the resulting two stereoisomers of the phenylpropanoid conjugate β-glutathionyl-γ-hydroxypropiovanillone (GS-HPV). We found that the Nu-class glutathione-S-transferase NaGST Nu is the only enzyme needed to remove glutathione from both (R)- and (S)-GS-HPV in N. aromaticivorans. We solved the crystal structure of NaGST Nu and used molecular modeling to propose a mechanism for the glutathione lyase (deglutathionylation) reaction in which an enzyme-stabilized glutathione thiolate attacks the thioether bond of GS-HPV, and the reaction proceeds through an enzyme-stabilized enolate intermediate. Three residues implicated in the proposed mechanism (Thr 51, Tyr 166, and Tyr 224) were found to be critical for the lyasemore » reaction. We also found that Nu-class GSTs from Sphingobium sp. SYK-6 (which can also break the β-aryl ether bond) and Escherichia coli (which cannot break the β-aryl ether bond) can also cleave (R)- and (S)-GS-HPV, suggesting that glutathione lyase activity may be common throughout this widespread but largely uncharacterized class of glutathione-S-transferases.« less
Authors:
 [1] ;  [2] ;  [1] ;  [1] ;  [3] ;  [1] ;  [2] ;  [4] ;  [5] ;  [6] ;  [7] ;  [8]
  1. Univ. of Wisconsin, Madison, WI (United States). Wisconsin Energy Institute and Department of Energy Great Lakes Bioenergy Research Center
  2. Univ. of Wisconsin, Madison, WI (United States). Department of Energy Great Lakes Bioenergy Research Center and Department of Biochemistry
  3. Univ. of Wisconsin, Madison, WI (United States). Department of Chemistry and Genome Center of Wisconsin
  4. Univ. of Wisconsin, Madison, WI (United States). Department of Chemistry
  5. Univ. of Wisconsin, Madison, WI (United States). Wisconsin Energy Institute, Department of Energy Great Lakes Bioenergy Research Center and Department of Biochemistry
  6. Univ. of Wisconsin, Madison, WI (United States). Wisconsin Energy Institute, Department of Energy Great Lakes Bioenergy Research Center and Civil and Environmental Engineering
  7. Univ. of Wisconsin, Madison, WI (United States). Wisconsin Energy Institute, Department of Energy Great Lakes Bioenergy Research Center, Department of Chemistry, Genome Center of Wisconsin and Department of Biomolecular Chemistry
  8. Univ. of Wisconsin, Madison, WI (United States). Wisconsin Energy Institute, Department of Energy Great Lakes Bioenergy Research Center and Department of Bacteriology
Publication Date:
Grant/Contract Number:
SC0018409; FC02-07ER64494; AC02-06CH11357
Type:
Accepted Manuscript
Journal Name:
Journal of Biological Chemistry
Additional Journal Information:
Journal Volume: 293; Journal Issue: 14; Journal ID: ISSN 0021-9258
Publisher:
American Society for Biochemistry and Molecular Biology
Research Org:
Great Lakes Bioenergy Research Center, Madison, WI (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Contributing Orgs:
Advanced Photon Source at Argonne National Laboratory
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Glutathione-S-transferases; Nu-class; β-aryl ether; deglutathionylation; Novosphingobium aromaticivorans; bacterial metabolism; enzyme mechanism; enzyme structure; lignin degradation; Escherichia coli
OSTI Identifier:
1459440