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Publication Abstract from PubMed

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 beta-aryl ether bond connecting most phenylpropanoid units of the lignin heteropolymer. Here, we tested three sphingomonads predicted to be capable of breaking the beta-aryl ether bond of the dimeric aromatic compound guaiacylglycerol-beta-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 beta-glutathionyl-gamma-hydroxypropiovanillone (GS-HPV). We found that the Nu-class glutathione-S-transferase NaGSTNu is the only enzyme needed to remove glutathione from both (R)- and (S)-GS-HPV in N. aromaticivorans We solved the crystal structure of NaGSTNu 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 that Nu-class GSTs from Sphingobium sp. SYK-6 (which can also break the beta-aryl ether bond) and Escherichia coli (which cannot break the beta-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.

Novosphingobium aromaticivorans uses a Nu-class glutathione-S-transferase as a glutathione lyase in breaking the beta-aryl ether bond of lignin.,Kontur WS, Bingman CA, Olmsted CN, Wassarman DR, Ulbrich A, Gall DL, Smith RW, Yusko LM, Fox BG, Noguera DR, Coon JJ, Donohue TJ J Biol Chem. 2018 Feb 15. pii: RA117.001268. doi: 10.1074/jbc.RA117.001268. PMID:29449375^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.