6GSC

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

Summary for 6GSC

• Entry DOI: 10.2210/pdb6gsc/pdb
• Descriptor: Superoxide dismutase, MANGANESE (II) ION, ... (4 entities in total)
• Functional Keywords: oxidoreductase, lignin valorisation, lignin oxidation, manganese keywds 2 superoxide dismutase, sphingobacterium
• Biological source: Sphingobacterium spiritivorum; More
• Total number of polymer chains: 2
• Total formula weight: 46056.18

Authors

Rashid, G.M.M.,Zhang, X.,Wilkinson, R.C.,Fulop, V.,Cottyn, B.,Baumberger, S.,Bugg, T.D.H. (deposition date: 2018-06-13, release date: 2018-10-03, Last modification date: 2024-01-17)

Primary citation

Rashid, G.M.M.,Zhang, X.,Wilkinson, R.C.,Fulop, V.,Cottyn, B.,Baumberger, S.,Bugg, T.D.H.
Sphingobacterium sp. T2 Manganese Superoxide Dismutase Catalyzes the Oxidative Demethylation of Polymeric Lignin via Generation of Hydroxyl Radical.
ACS Chem. Biol., 13:2920-2929, 2018

PubMed 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-Cα oxidative cleavage and demethylation, as well as alkene dihydroxylation and alcohol oxidation. O labeling studies on the SpMnSOD-catalyzed oxidation of lignin model compound guiaiacylglycerol-β-guaiacyl ether indicated that the an oxygen atom inserted by the enzyme is derived from superoxide or peroxide. Analysis of an alkali lignin treated by SpMnSOD1 by quantitative P 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 4.1 molar equivalents 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 P 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 center for hydroxyl radical generation.

PubMed: 30247873
DOI: 10.1021/acschembio.8b00557

Experimental method

X-RAY DIFFRACTION (1.32 Å)