Wolucka Beata A, Communi David
Laboratory of Mycobacterial Biochemistry, Pasteur Institute of Brussels, Institute of Public Health, Belgium.
FEBS J. 2006 Oct;273(19):4435-45. doi: 10.1111/j.1742-4658.2006.05443.x. Epub 2006 Sep 5.
The last step of the biosynthesis of L-ascorbic acid (vitamin C) in plants and animals is catalyzed by L-gulono-1,4-lactone oxidoreductases, which use both L-gulono-1,4-lactone and L-galactono-1,4-lactone as substrates. L-gulono-1,4-lactone oxidase is missing in scurvy-prone, vitamin C-deficient animals, such as humans and guinea pigs, which are also highly susceptible to tuberculosis. A blast search using the rat L-gulono-1,4-lactone oxidase sequence revealed the presence of closely related orthologs in a limited number of bacterial species, including several pathogens of human lungs, such as Mycobacterium tuberculosis, Pseudomonas aeruginosa, Burkholderia cepacia and Bacillus anthracis. The genome of M. tuberculosis, the etiologic agent of tuberculosis, encodes a protein (Rv1771) that shows 32% identity with the rat L-gulono-1,4-lactone oxidase protein. The Rv1771 gene was cloned and expressed in Escherichia coli, and the corresponding protein was affinity-purified and characterized. The FAD-binding motif-containing Rv1771 protein is a metalloenzyme that oxidizes L-gulono-1,4-lactone (Km 5.5 mm) but not L-galactono-1,4-lactone. The enzyme has a dehydrogenase activity and can use both cytochrome c (Km 4.7 microm) and phenazine methosulfate as exogenous electron acceptors. Molecular oxygen does not serve as a substrate for the Rv1771 protein. Dehydrogenase activity was measured in cellular extracts of a Mycobacterium bovis BCG strain. In conclusion, M. tuberculosis produces a novel, highly specific L-gulono-1,4-lactone dehydrogenase (Rv1771) and has the capacity to synthesize vitamin C.
植物和动物体内L-抗坏血酸（维生素C）生物合成的最后一步由L-古洛糖酸-1,4-内酯氧化还原酶催化，该酶以L-古洛糖酸-1,4-内酯和L-半乳糖酸-1,4-内酯作为底物。在易患坏血病、缺乏维生素C的动物（如人类和豚鼠）中，L-古洛糖酸-1,4-内酯氧化酶缺失，这些动物也极易感染结核病。使用大鼠L-古洛糖酸-1,4-内酯氧化酶序列进行的Blast搜索显示，在有限数量的细菌物种中存在密切相关的直系同源物，包括几种人类肺部病原体，如结核分枝杆菌、铜绿假单胞菌、洋葱伯克霍尔德菌和炭疽芽孢杆菌。结核病的病原体结核分枝杆菌的基因组编码一种与大鼠L-古洛糖酸-1,4-内酯氧化酶蛋白具有32%同一性的蛋白质（Rv1771）。Rv1771基因被克隆并在大肠杆菌中表达，相应的蛋白质经过亲和纯化和表征。含有FAD结合基序的Rv1771蛋白是一种金属酶，可氧化L-古洛糖酸-1,4-内酯（Km为5.5 mM），但不能氧化L-半乳糖酸-1,4-内酯。该酶具有脱氢酶活性，可使用细胞色素c（Km为4.7 μM）和吩嗪硫酸甲酯作为外源电子受体。分子氧不是Rv1771蛋白的底物。在卡介苗结核分枝杆菌菌株的细胞提取物中测量了脱氢酶活性。总之，结核分枝杆菌产生一种新型、高度特异性的L-古洛糖酸-1,4-内酯脱氢酶（Rv1771），并具有合成维生素C的能力。
