Stereochemical Features of Glutathione-dependent Enzymes in the Sphingobium sp. Strain SYK-6 β-Aryl Etherase Pathway
- University of Wisconsin, Madison, WI (United States)
Glutathione-dependent enzymes play important protective, repair, or metabolic roles in cells. In particular, enzymes in the glutathione S-transferase (GST) superfamily function in stress responses, defense systems, or xenobiotic detoxification. Here, we identify novel features of bacterial GSTs that cleave -aryl ether bonds typically found in plant lignin. Our data reveal several original features of the reaction cycle of these GSTs, including stereospecific substrate recognition and stereoselective formation of -S-thioether linkages. Products of recombinant GSTs (LigE, LigP, and LigF) are -S-glutathionyl--ketothioethers that are degraded by a -S-thioetherase (LigG). All three Lig GSTs produced the ketone product (-S-glutathionyl- -veratrylethanone) from an achiral side chain-truncated model substrate (-guaiacyl--veratrylethanone). However, when -etherase assays were conducted with a racemic model substrate, -guaiacyl--veratrylglycerone, LigE- or LigP-catalyzed reactions yielded only one of two potential product (-Sglutathionyl--veratrylglycerone) epimers, whereas the other diastereomer (differing in configuration at the -position (i.e. its-epimer)) was produced only in the LigF-catalyzed reaction. Thus, -etherase catalysis causes stereochemical inversion of the chiral center, converting a (R)-substrate to a (S)-product (LigE and LigP), and a (S)-substrate to a (R)-product (LigF). Further, LigG catalyzed glutathione-dependent -S-thioether cleavage with-S-glutathionyl--veratrylethanone and with(R)- configured -S-glutathionyl--veratrylglycerone but exhibited no or significantly reduced -S-thioether-cleaving activity with the (S)-epimer, demonstrating that LigG is a stereospecific -thioetherase. We therefore propose that multiple Lig enzymes are needed in this -aryl etherase pathway in order to cleave the racemic -ether linkages that are present in the backbone of the lignin polymer.
- Research Organization:
- Univ. of Wisconsin, Madison, WI (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- Grant/Contract Number:
- FC02-07ER64494
- OSTI ID:
- 1904221
- Journal Information:
- Journal of Biological Chemistry, Vol. 289, Issue 12; ISSN 0021-9258
- Publisher:
- American Society for Biochemistry and Molecular BiologyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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