Reckenfelderbäumer N, Lüdemann H, Schmidt H, Steverding D, Krauth-Siegel R L
Biochemie-Zentrum Heidelberg, Universität Heidelberg, 69120 Heidelberg, Germany.
J Biol Chem. 2000 Mar 17;275(11):7547-52. doi: 10.1074/jbc.275.11.7547.
Trypanosomes and Leishmania, the causative agents of several tropical diseases, lack the glutathione/glutathione reductase system but have trypanothione/trypanothione reductase instead. The uniqueness of this thiol metabolism and the failure to detect thioredoxin reductases in these parasites have led to the suggestion that these protozoa lack a thioredoxin system. As presented here, this is not the case. A gene encoding thioredoxin has been cloned from Trypanosoma brucei, the causative agent of African sleeping sickness. The single copy gene, which encodes a protein of 107 amino acid residues, is expressed in all developmental stages of the parasite. The deduced protein sequence is 56% identical with a putative thioredoxin revealed by the genome project of Leishmania major. The relationship to other thioredoxins is low. T. brucei thioredoxin is unusual in having a calculated pI value of 8.5. The gene has been overexpressed in Escherichia coli. The recombinant protein is a substrate of human thioredoxin reductase with a K(m) value of 6 microM but is not reduced by trypanothione reductase. T. brucei thioredoxin catalyzes the reduction of insulin by dithioerythritol, and functions as an electron donor for T. brucei ribonucleotide reductase. The parasite protein is the first classical thioredoxin of the order Kinetoplastida characterized so far.
锥虫和利什曼原虫是几种热带疾病的病原体，它们缺乏谷胱甘肽/谷胱甘肽还原酶系统，但具有锥虫硫醇/锥虫硫醇还原酶。这种硫醇代谢的独特性以及在这些寄生虫中未能检测到硫氧还蛋白还原酶，导致有人提出这些原生动物缺乏硫氧还蛋白系统。但如本文所述，情况并非如此。已经从非洲昏睡病的病原体布氏锥虫中克隆出了一个编码硫氧还蛋白的基因。这个单拷贝基因编码一个由107个氨基酸残基组成的蛋白质，在寄生虫的所有发育阶段都有表达。推导的蛋白质序列与大利什曼原虫基因组计划揭示的一个假定硫氧还蛋白有56%的同一性。与其他硫氧还蛋白的关系较低。布氏锥虫硫氧还蛋白的一个不寻常之处在于其计算出的pI值为8.5。该基因已在大肠杆菌中过表达。重组蛋白是人类硫氧还蛋白还原酶的底物，K(m)值为6微摩尔，但不能被锥虫硫醇还原酶还原。布氏锥虫硫氧还蛋白催化二硫赤藓糖醇对胰岛素的还原，并作为布氏锥虫核糖核苷酸还原酶的电子供体。该寄生虫蛋白是迄今所鉴定的动质体目第一个经典硫氧还蛋白。
