title: Degradation of Diphenyl Ether in Sphingobium phenoxybenzoativorans SC_3 Is Initiated by a Novel Ring Cleavage Dioxygenase.
abstract: Sphingobium phenoxybenzoativoransSC_3 degrades and utilizes diphenyl ether (DE) or 2-carboxy-DE as its sole carbon and energy source. In this study, we report the degradation of DE and 2-carboxy-DE initiated by a novel ring cleavage angular dioxygenase (diphenyl ether dioxygenase [Dpe]) in the strain. Dpe functions at the angular carbon and its adjacent carbon (C-1a, C-2) of a benzene ring in DE (or the 2-carboxybenzene ring in 2-carboxy-DE) and cleaves the C-1a-C-2 bond (decarboxylation occurs simultaneously for 2-carboxy-DE), yielding 2,4-hexadienal phenyl ester, which is subsequently hydrolyzed to muconic acid semialdehyde and phenol. Dpe is a type IV Rieske non-heme iron oxygenase (RHO) and consists of three components: a hetero-oligomer oxygenase, a [2Fe-2S]-type ferredoxin, and a glutathione reductase (GR)-type reductase. Genetic analyses revealed thatdpeA1A2plays an essential role in the degradation and utilization of DE and 2-carboxy-DE inS. phenoxybenzoativoransSC_3. Enzymatic study showed that transformation of 1 molecule of DE needs two molecules of oxygen and two molecules of NADH, supporting the assumption that the cleavage of DE catalyzed by Dpe is a continuous two-step dioxygenation process: DE is dioxygenated at C-1a and C-2 to form a hemiacetal-like intermediate, which is further deoxygenated, resulting in the cleavage of the C-1a-C-2 bond to form one molecule of 2,4-hexadienal phenyl ester and two molecules of H2O. This study extends our knowledge of the mode and mechanism of ring cleavage of aromatic compounds.IMPORTANCEBenzene ring cleavage, catalyzed by dioxygenase, is the key and speed-limiting step in the aerobic degradation of aromatic compounds. As previously reported, in the ring cleavage of DEs, the benzene ring needs to be first dihydroxylated at a lateral position and subsequently dehydrogenated and opened through extradiol cleavage. This process requires three enzymes (two dioxygenases and one dehydrogenase). In this study, we identified a novel angular dioxygenase (Dpe) inS. phenoxybenzoativoransSC_3. Under Dpe-mediated catalysis, the benzene ring of DE is dioxygenated at the angular position (C-1a, C-2), resulting in the cleavage of the C-1a-C-2 bond to generate a novel product, 2,4-hexadienal phenyl ester. This process needs only one angular dioxygenase, Dpe. Thus, the ring cleavage catalyzed by Dpe represents a novel mechanism of benzene ring cleavage.
authors.affiliation: Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu, China.|The Institute of Agricultural Resources and Environment, Jiangsu Academy of Agricultural Sciences, Nanjing, Jiangsu, China.
authors.forename: Shu
authors.initials: S
authors.lastname: Cai
authors.affiliation: The College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, Jiangsu, China.
authors.forename: Li-Wei
authors.initials: LW
authors.lastname: Chen
authors.affiliation: The Institute of Agricultural Resources and Environment, Jiangsu Academy of Agricultural Sciences, Nanjing, Jiangsu, China.
authors.forename: Yu-Chun
authors.initials: YC
authors.lastname: Ai
authors.affiliation: Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu, China.
authors.forename: Ji-Guo
authors.initials: JG
authors.lastname: Qiu
authors.affiliation: College of Basic Medical Science, Jiujiang University, Jiujiang, Jiangxi, China.
authors.forename: Cheng-Hong
authors.initials: CH
authors.lastname: Wang
authors.affiliation: Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu, China.
authors.forename: Chao
authors.initials: C
authors.lastname: Shi
authors.affiliation: Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu, China hejian@njau.edu.cn ctm@njau.edu.cn.
authors.forename: Jian
authors.initials: J
authors.lastname: He
authors.affiliation: The College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, Jiangsu, China hejian@njau.edu.cn ctm@njau.edu.cn.
authors.forename: Tian-Ming
authors.initials: TM
authors.lastname: Cai
mesh_terms: D020561:Alphaproteobacteria / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D055162:Biocatalysis; D001673:Biodegradation, Environmental; D049308:Dioxygenases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015394:Molecular Structure; D010647:Phenyl Ethers / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D010647:Phenyl Ethers; C031538:phenyl ether; D049308:Dioxygenases
keywords: 2-carboxydiphenyl ether; Dpe; Sphingobium; angular dioxygenase; diphenyl ether