ABSTRACT
The carbazole 1,9a-dioxygenase (CARDO) system of
Pseudomonas resinovorans
strain CA10 consists of terminal oxygenase (CarAa), ferredoxin (CarAc), and ferredoxin reductase (CarAd). Each component of CARDO was expressed in
Escherichia coli
strain BL21(DE3) as a native form (CarAa) or a His-tagged form (CarAc and CarAd) and was purified to apparent homogeneity. CarAa was found to be trimeric and to have one Rieske type [2Fe-2S] cluster and one mononuclear iron center in each monomer. Both His-tagged proteins were found to be monomeric and to contain the prosthetic groups predicted from the deduced amino acid sequence (His-tagged CarAd, one FAD and one [2Fe-2S] cluster per monomer protein; His-tagged CarAc, one Rieske type [2Fe-2S] cluster per monomer protein). Both NADH and NADPH were effective as electron donors for His-tagged CarAd. However, since the
k
cat
/
K
m
for NADH is 22.3-fold higher than that for NADPH in the 2,6-dichlorophenolindophenol reductase assay, NADH was supposed to be the physiological electron donor of CarAd. In the presence of NADH, His-tagged CarAc was reduced by His-tagged CarAd. Similarly, CarAa was reduced by His-tagged CarAc, His-tagged CarAd, and NADH. The three purified proteins could reconstitute the CARDO activity in vitro. In the reconstituted CARDO system, His-tagged CarAc seemed to be indispensable for electron transport, while His-tagged CarAd could be replaced by some unrelated reductases.
摘要
resinovorans 假单胞菌的咔唑 1,9a-二氧合酶(CARDO)系统
树脂假单胞菌
菌株 CA10 的咔唑 1,9a-二氧化酶(CARDO)系统由末端加氧酶(CarAa)、铁氧还原酶(CarAc)和铁氧还原酶(CarAd)组成。CARDO 的每个组分都在
大肠杆菌
菌株 BL21(DE3)中以原生形式(CarAa)或 His 标记形式(CarAc 和 CarAd)表达 CARDO,并纯化至明显均一。发现 CarAa 为三聚体,每个单体中有一个 Rieske 型 [2Fe-2S] 簇和一个单核铁中心。两种 His 标记的蛋白质均为单体,并含有推导出的氨基酸序列所预测的修复基团(His 标记的 CarAd,每个单体蛋白质含有一个 FAD 和一个 [2Fe-2S] 簇;His 标记的 CarAc,每个单体蛋白质含有一个 Rieske 型 [2Fe-2S] 簇)。对于 His 标记的 CarAd,NADH 和 NADPH 都是有效的电子供体。然而,由于
k
cat
/
K
m
在 2,6-二氯苯酚靛酚还原酶试验中,NADH 的 K m 是 NADPH 的 22.3 倍,因此 NADH 应该是 CarAd 的生理电子供体。在 NADH 存在的情况下,His 标记的 CarAc 被 His 标记的 CarAd 还原。同样,CarAa 也被 His 标记的 CarAc、His 标记的 CarAd 和 NADH 还原。这三种纯化蛋白可以在体外重组 CARDO 活性。在重组的 CARDO 系统中,His 标记的 CarAc 似乎是电子传递所不可或缺的,而 His 标记的 CarAd 则可以被一些不相关的还原酶所取代。