Coexistence of two different O demethylation systems in lignin metabolism by Sphingomonas paucimobilis SYK-6: cloning and sequencing of the lignin biphenyl-specific O-demethylase (LigX) gene
| Autor: | Eiji Masai, Motoo Higashi, Sachiko Kubota, Tomonori Sonoki, Yoshihiro Katayama, Takahiro Obi |
|---|---|
| Rok vydání: | 2000 |
| Předmět: |
Oxygenase
Sphingomonas paucimobilis Oxidoreductases O-Demethylating Cytochrome Genetics and Molecular Biology Applied Microbiology and Biotechnology Lignin Sphingomonas chemistry.chemical_compound Bacterial Proteins Escherichia coli Cloning Molecular Phylogeny Demethylation chemistry.chemical_classification Ecology biology Monooxygenase biology.organism_classification Recombinant Proteins Metabolic pathway Kinetics Enzyme chemistry Biochemistry Models Chemical biology.protein Dimerization Food Science Biotechnology |
| Zdroj: | Applied and environmental microbiology. 66(5) |
| ISSN: | 0099-2240 |
| Popis: | Lignin is the most abundant aromatic compound in the biosphere. The degradation of lignin is a significant step in the global carbon cycle. Some bacterial strains are capable of degrading aromatic compounds. With rare exceptions, they do not open the aromatic ring unless two hydroxyl groups have been introduced in cis into the benzene nucleus. For example, the phenylmethylether bond exists in natural aromatic compounds such as lignin; its cleavage is essential to prepare the substrate of enzyme for lignin metabolism in the biosphere. Some studies have investigated the cleavage of this phenylmethylether bond by an oxygenase reaction or by the tetrahydrofolate (THF)-dependent methyltransferase reaction system (2, 5–9, 11, 17, 28, 36, 37, 39, 40). In the former reaction, monooxygenases with two- or three-component enzyme systems catalyzed methylether cleavage; these enzyme systems contained terminal enzymes such as iron-sulfur proteins and cytochrome P450-like enzymes (6–9), and they required NADH or NADPH to carry out O demethylation via electron transport. Some reports showed that in the THF-dependent methyltransferase reaction system, ATP and dl-THF are essential for O demethylation reactions (5, 17, 37). However, successful molecular cloning of the O demethylation system genes has been described in a few reports. In the oxygenase reaction system, vanillate demethylase genes such as vanA and vanB of Pseudomonas sp. strains ATCC 19151 (7) and HR199 (36), whose products catalyzed vanillate O demethylation, have been described. vanA and vanB encode the subunits of the vanillate O demethylase (class I type oxygenase). In the THF-dependent methyltransferase reaction, we previously reported that ligH of Sphingomonas paucimobilis SYK-6 was essential to THF-dependent O demethylation of vanillate and syringate (28). And Kaufmann et al. succeeded in the molecular cloning of odmA, which is involved in the THF-dependent methyltransferase reaction of vanillate in Acetobacterium dehalogenans (18). S. paucimobilis SYK-6, a bacterium that can grow on 5,5′-dehydrodivanillic acid (2,2′-dihydroxy-3,3′-dimethoxy-5,5′-dicarboxybiphenyl) (DDVA) as a sole carbon source, was isolated from pulp-bleaching wastewater in Japan. This bacterium can also grow on several dimeric model compounds of lignin. The metabolic pathway of DDVA and other dimeric model compounds of lignin in this bacterium has been reported previously (15, 28). We have identified several genes related to this pathway (21–25, 28, 30, 31, 34, 35). It has O demethylation systems that work on three kinds of substrates, DDVA, syringate, and vanillate, in the metabolic pathway (15, 28). The O demethylation of syringate and vanillate in SYK-6 was carried out by the THF-dependent enzyme system containing ligH, but this system had no activity on DDVA (28). These results pose important questions. How does DDVA O demethylation proceed in the metabolism of lignin model compounds by S. paucimobilis SYK-6? Is the enzyme system of DDVA O demethylation of the THF-dependent methyltransferase type or the oxygenative demethylation type? In this study, we investigated DDVA O demethylation in SYK-6. This is the first report of an O demethylase acting on biphenyl type lignin. We first showed that two different demethylation systems exist in S. paucimobilis SYK-6: one is a DDVA-specific oxygenative O-demethylase, and the other is a syringate- and vanillate-specific O-demethylase of the THF-dependent methyltransferase type. |
| Databáze: | OpenAIRE |
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