Identification of Manganese Superoxide Dismutase from Sphingobacterium sp. T2 as a Novel Bacterial Enzyme for Lignin Oxidation

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• 作者：Goran M. M. Rashid ; Charles R. Taylor ; Yangqingxue Liu ; Xiaoyang Zhang ; Dean Rea ; Vilmos F眉l枚p ; Timothy D. H. Bugg
• 刊名：ACS Chemical Biology
• 出版年：2015
• 出版时间：October 16, 2015
• 年：2015
• 卷：10
• 期：10
• 页码：2286-2294
• 全文大小：521K
• ISSN：1554-8937

文摘

The valorization of aromatic heteropolymer lignin is an important unsolved problem in the development of a biomass-based biorefinery, for which novel high-activity biocatalysts are needed. Sequencing of the genomic DNA of lignin-degrading bacterial strain Sphingobacterium sp. T2 revealed no matches to known lignin-degrading genes. Proteomic matches for two manganese superoxide dismutase proteins were found in partially purified extracellular fractions. Recombinant MnSOD1 and MnSOD2 were both found to show high activity for oxidation of Organosolv and Kraft lignin, and lignin model compounds, generating multiple oxidation products. Structure determination revealed that the products result from aryl鈥揅_伪 and C_伪鈥揅_尾 bond oxidative cleavage and O-demethylation. The crystal structure of MnSOD1 was determined to 1.35 脜 resolution, revealing a typical MnSOD homodimer harboring a five-coordinate trigonal bipyramidal Mn(II) center ligated by three His, one Asp, and a water/hydroxide in each active site. We propose that the lignin oxidation reactivity of these enzymes is due to the production of a hydroxyl radical, a highly reactive oxidant. This is the first demonstration that MnSOD is a microbial lignin-oxidizing enzyme.