Catalytic Mechanism of Aryl-Ether Bond Cleavage in Lignin by LigF and LigG
[2];
[3];
[4]
- National Renewable Energy Lab. (NREL), Golden, CO (United States). National Bioenergy Center; Univ. of Campinas (UNICAMP), Sao Paulo (Brazil). Inst. of Chemistry and Center for Computing in Engineering and Sciences
- National Renewable Energy Lab. (NREL), Golden, CO (United States). Biosciences Center
- Univ. of Campinas (UNICAMP), Sao Paulo (Brazil). Inst. of Chemistry and Center for Computing in Engineering and Sciences
- National Renewable Energy Lab. (NREL), Golden, CO (United States). National Bioenergy Center
Given the abundance of lignin in nature, multiple enzyme systems have been discovered to cleave the β-O-4 bonds, the most prevalent intermonomer linkage. In particular, stereospecific cleavage of lignin oligomers by glutathione S-transferases (GSTs) has been reported in several sphingomonads. Here in this paper, we apply quantum mechanics/molecular mechanics simulations to study the mechanism of two glutathione-dependent enzymes in the β-aryl ether catabolic pathway of Sphingomonas sp. SYK-6, namely, LigF, a β-etherase, and LigG, a lyase. For LigF, the free-energy landscape supports a SN2 reaction mechanism, with the monoaromatic leaving group being promptly neutralized upon release. Specific interactions with conserved residues are responsible for stereoselectivity and for activation of the cofactor as a nucleophile. A glutathione conjugate is also released by LigF and serves the substrate of LigG, undergoing a SN2-like reaction, in which Cys15 acts as the nucleophile, to yield the second monoaromatic product. The simulations suggest that the electron-donating substituent at the para-position found in lignin-derived aromatics and the interaction with Tyr217 are essential for reactivity in LigG. Overall, this work deepens the understanding of the stereospecific enzymatic mechanisms in the β-aryl ether cleavage pathway and reveals key structural features underpinning the ligninolytic activity detected in several sphingomonad GSTs.
- Research Organization:
- National Renewable Energy Lab. (NREL), Golden, CO (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), Sustainable Transportation Office. Bioenergy Technologies Office; USDOE Office of Science (SC), Biological and Environmental Research (BER); São Paulo Research Foundation (FAPESP)
- Grant/Contract Number:
- AC36-08GO28308; 2016/04775-5; 2013/08293-7; AC05-00OR22725
- OSTI ID:
- 1578254
- Alternate ID(s):
- OSTI ID: 1607161
- Report Number(s):
- NREL/JA-2700-75435
- Journal Information:
- Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry, Vol. 123, Issue 48; ISSN 1520-6106
- Publisher:
- American Chemical SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
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