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Sphingobacterium sp. T2 manganese superoxide dismutase catalyses the oxidative demethylation of polymeric lignin via generation of hydroxyl radical

DOI: 10.1021/acschembio.8b00557 DOI Help

Authors: Goran M. M. Rashid (University of Warwick) , Xiaoyang Zhang (University of Warwick) , Rachael C. Wilkinson (University of Warwick) , Vilmos Fulop (University of Warwick) , Betty Cottyn (CNRS, Université Paris-Saclay) , Stéphanie Baumberger (CNRS, Université Paris-Saclay) , Timothy D. H. Bugg (University of Warwick)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Acs Chemical Biology

State: Published (Approved)
Published: September 2018
Diamond Proposal Number(s): 14692

Abstract: Sphingobacterium sp. T2 contains two extracellular manganese superoxide dismutase enzymes which exhibit unprecedented activity for lignin oxidation, but via an unknown mechanism. Enzymatic treatment of lignin model compounds gave products whose structures were indicative of aryl-C oxidative cleavage and demethylation, as well as alkene dihydroxylation and alcohol oxidation. 18O labelling studies on the SpMnSOD-catalysed oxidation of lignin model compound guiaiacylglycerol--guaiacyl ether indicated that the oxygen atom inserted by the enzyme is derived from superoxide or peroxide. Analysis of an alkali lignin treated by SpMnSOD1 by quantitative 31P NMR spectroscopy demonstrated 20-40% increases in phenolic and aliphatic OH content, consistent with lignin demethylation and some internal oxidative cleavage reactions. Assay for hydroxyl radical generation using a fluorometric hydroxyphenylfluorescein assay revealed the release of approximately 1 molar equivalent of hydroxyl radical by SpMnSOD1. Four amino acid replacements in SpMnSOD1 were investigated, and A31H or Y27H site-directed mutant enzymes were found to show no lignin demethylation activity according to 31P NMR analysis. Structure determination of the A31H and Y27H mutant enzymes reveals the repositioning of an N-terminal protein loop, leading to widening of a solvent channel at the dimer interface, which would provide increased solvent access to the Mn centre for hydroxyl radical generation.

Journal Keywords: lignin depolymerisation; manganese superoxide dismutase; Sphingobacterium sp. T2;

Diamond Keywords: Bacteria; Enzymes

Subject Areas: Biology and Bio-materials, Chemistry

Instruments: I03-Macromolecular Crystallography

Added On: 01/10/2018 12:06

Discipline Tags:

Biochemistry Catalysis Chemistry Structural biology Life Sciences & Biotech

Technical Tags:

Diffraction Macromolecular Crystallography (MX)