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

Abstract

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 (Thr⁵¹, Tyr¹⁶⁶, and Tyr²²⁴) were found to be critical for the lyase reaction. We also found thatmore » 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:

Kontur, Wayne S.; Bingman, Craig A.; Olmsted, Charles N.; Wassarman, Douglas R.; Ulbrich, Arne; Gall, Daniel L.; Smith, Robert W.; Yusko, Larissa M.; Fox, Brian G.; Noguera, Daniel R.; Coon, Joshua J.; Donohue, Timothy J.

Publication Date:

Sun Apr 01 00:00:00 EDT 2018

Research Org.:

Great Lakes Bioenergy Research Center (GLBRC), Madison, WI (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER)

Contributing Org.:

Advanced Photon Source at Argonne National Laboratory

OSTI Identifier:

1772667

Alternate Identifier(s):

OSTI ID: 1459440

Grant/Contract Number:  

DOE Office of Science BER DE-FC02–07ER64494; DOE Office of Science BER DE-SC0018409; SC0018409; FC02-07ER64494; AC02-06CH11357

Resource Type:

Published Article

Journal Name:

Journal of Biological Chemistry

Additional Journal Information:

Journal Name: Journal of Biological Chemistry Journal Volume: 293 Journal Issue: 14; Journal ID: ISSN 0021-9258

Publisher:

Elsevier

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