Nojiri Hideaki
Biotechnology Research Center, The University of Tokyo, Tokyo, Japan.
Biosci Biotechnol Biochem. 2012;76(1):1-18. doi: 10.1271/bbb.110620. Epub 2012 Jan 7.
Carbazole degradation by several bacterial strains, including Pseudomonas resinovorans CA10, has been investigated over the last two decades. As the initial reaction in degradation pathways, carbazole is commonly oxygenated at angular (C9a) and adjacent (C1) carbons as two hydroxyl groups in a cis configuration. This type of dioxygenation is termed "angular dioxygenation," and is catalyzed by carbazole 1,9a-dioxygenase (CARDO), consisting of terminal oxygenase, ferredoxin, and ferredoxin reductase components. The crystal structures of all components and the electron transfer complex between terminal oxygenase and ferredoxin indicate substrate recognition mechanisms suitable for angular dioxygenation and specific electron transfer among the three components. In contrast, the carbazole degradative car operon of CA10 is located on IncP-7 conjugative plasmid pCAR1. Together with conventional molecular genetic and biochemical investigations, recent genome sequencing and RNA mapping studies have clarified that transcriptional cross-regulation via nucleoid-associated proteins is established between pCAR1 and the host chromosome.
在过去二十年中，人们对包括树脂糖假单胞菌CA10在内的几种细菌菌株降解咔唑的情况进行了研究。作为降解途径中的初始反应，咔唑通常在角位（C9a）和相邻（C1）碳原子上被氧化为两个呈顺式构型的羟基。这种双加氧反应类型被称为“角位双加氧反应”，由咔唑1,9a - 双加氧酶（CARDO）催化，该酶由末端加氧酶、铁氧化还原蛋白和铁氧化还原蛋白还原酶组分组成。所有组分的晶体结构以及末端加氧酶与铁氧化还原蛋白之间的电子传递复合物表明了适合角位双加氧反应的底物识别机制以及这三个组分之间特定的电子传递。相比之下，CA10的咔唑降解操纵子car位于IncP - 7接合质粒pCAR1上。结合传统的分子遗传学和生化研究，最近的基因组测序和RNA图谱研究已经阐明，通过类核相关蛋白建立了pCAR1与宿主染色体之间的转录交叉调控。
