Catalytic Mechanism of Aryl-Ether Bond Cleavage in Lignin by LigF and LigG [electronic resource]

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Ngôn ngữ: eng

Ký hiệu phân loại: 666.9 Masonry adhesives

Thông tin xuất bản: Washington, D.C. : Oak Ridge, Tenn. : United States. Dept. of Energy. Office of Energy Efficiency and Renewable Energy ; Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2019

Mô tả vật lý: Size: p. 10142-10151 : , digital, PDF file.

Bộ sưu tập: Metadata

ID: 264190

 Given the abundance of lignin in nature, multiple enzyme systems have been discovered to cleave the ?-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 ?-aryl ether catabolic pathway of <
 em>
 Sphingomonas sp.<
 /em>
  SYK-6, namely, LigF, a ?-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 S<
 sub>
 N<
 /sub>
 2-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 ?-aryl ether cleavage pathway and reveals key structural features underpinning the ligninolytic activity detected in several sphingomonad GSTs.
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