ABSTRACT
Sphingobium
sp. strain SYK-6 is able to degrade various lignin-derived biaryls, including a phenylcoumaran-type compound, dehydrodiconiferyl alcohol (DCA). In SYK-6 cells, the alcohol group of the B-ring side chain of DCA is initially oxidized to the carboxyl group to generate 3-(2-(4-hydroxy-3-methoxyphenyl)-3-(hydroxymethyl)-7-methoxy-2,3-dihydrobenzofuran-5-yl) acrylic acid (DCA-C). Next, the alcohol group of the A-ring side chain of DCA-C is oxidized to the carboxyl group, and then the resulting metabolite is catabolized through vanillin and 5-formylferulate. In this study, the genes involved in the conversion of DCA-C were identified and characterized. The DCA-C oxidation activities in SYK-6 were enhanced in the presence of flavin adenine dinucleotide and an artificial electron acceptor and were induced ca. 1.6-fold when the cells were grown with DCA. Based on these observations, SLG_09480 (
phcC
) and SLG_09500 (
phcD
), encoding glucose-methanol-choline oxidoreductase family proteins, were presumed to encode DCA-C oxidases. Analyses of
phcC
and
phcD
mutants indicated that PhcC and PhcD are essential for the conversion of (+)-DCA-C and (−)-DCA-C, respectively. When
phcC
and
phcD
were expressed in SYK-6 and
Escherichia coli
, the gene products were mainly observed in their membrane fractions. The membrane fractions of
E. coli
that expressed
phcC
and
phcD
catalyzed the specific conversion of DCA-C into the corresponding carboxyl derivatives. In the oxidation of DCA-C, PhcC and PhcD effectively utilized ubiquinone derivatives as electron acceptors. Furthermore, the transcription of a putative cytochrome
c
gene was significantly induced in SYK-6 grown with DCA. The DCA-C oxidation catalyzed by membrane-associated PhcC and PhcD appears to be coupled to the respiratory chain.
摘要
Sphingobium
菌株 SYK-6 能够降解各种木质素衍生双芳基,包括一种苯基香豆素类化合物--脱氢双铁醇(DCA)。在 SYK-6 细胞中,DCA 的 B 环侧链上的醇基首先被氧化成羧基,生成 3-(2-(4-羟基-3-甲氧基苯基)-3-(羟甲基)-7-甲氧基-2,3-二氢苯并呋喃-5-基)丙烯酸(DCA-C)。接着,DCA-C 的 A 环侧链上的醇基会被氧化成羧基,然后产生的代谢物会通过香兰素和 5-甲酰阿魏酸酯进行分解。本研究确定了参与 DCA-C 转化的基因并对其进行了表征。在黄素腺嘌呤二核苷酸和人工电子受体存在的情况下,SYK-6 中的 DCA-C 氧化活性增强,当细胞与 DCA 一起生长时,DCA-C 氧化活性被诱导约 1.6 倍。基于这些观察结果,SLG_09480 (
phcC
) 和 SLG_09500 (
phcD
) 编码葡萄糖-甲醇-胆碱氧化还原酶家族蛋白,被推测编码 DCA-C 氧化酶。对
phcC
和
突变体
突变体的分析表明,PhcC 和 PhcD 分别对 (+)-DCA-C 和 (-)-DCA-C 的转化至关重要。当
phcC
和
phcD
在 SYK-6 和
大肠杆菌
中表达,其基因产物主要存在于它们的膜分馏物中。大肠杆菌
大肠杆菌
表达
phcC
和
phcD
催化了 DCA-C 向相应羧基衍生物的特定转化。在氧化 DCA-C 的过程中,PhcC 和 PhcD 有效地利用了泛醌衍生物作为电子受体。此外,一种假定的细胞色素
c
基因的转录。膜相关 PhcC 和 PhcD 催化的 DCA-C 氧化似乎与呼吸链相关联。