SUBSTRATE RECOGNITION IN MULTIDRUG RESISTANCE

在大肠杆菌中，临床耐药质粒R773携带 砷抗性(Ars)操纵子，产生对砷酸盐的抗性， 亚砷酸盐、亚硫酸盐和亚碲酸盐。操纵子编码一个系统，用于 将生物能量转化为有毒物质的解毒 含氧阴离子亚砷酸盐(As+3)和锑(Sb+3)的三磷酸腺苷挤压 阴离子。因为操纵子也会抵抗无关的 含氧阴离子砷(As+5)和碲酸盐(Te+4)，Ars体系是真实的 多药耐药。这个操纵子产生的机制 对多种无关化合物的抗性构成了这一现象的基础 求婚。 对砷和碲酸盐的抗性除了需要arsC基因之外 氧离子泵的基因。ArsC蛋白是第一个被发现的 一类新的还原酶的成员。这种新型的酶能催化还原 含氧阴离子，扩大了对砷酸盐和亚碲酸盐的抗性范围 通过将这些含氧阴离子转化为泵浦底物。这种酶用来 谷胱甘肽作为还原剂的来源，并被假定为直接 连接到氧阴离子泵。因此，这个系统是细菌的类似物 高等生物中谷胱甘肽-S-转移酶结合系统的研究 为人类和人类的抵抗机制提供了良好的模型系统 动物。这个项目的总体目标是首先，阐明 ArsC蛋白的酶机制，第二，它的作用 抗性中的蛋白质。

In Escherichia coli the clinical resistance plasmid R773 carries the arsenical resistance (ars) operon, which produces resistance to arsenate, arsenite, antimonite and tellurite. The operon encodes a system for the transduction of biological energy into the detoxification of toxic oxyanions arsenite (As+3), and antimonite (Sb+3) by ATP-driven extrusion of the anions. Since the operon also gives resistance to the unrelated oxyanions arsenate (As+5) and tellurite (Te+4), the Ars system is a true multidrug resistance. The mechanism by which this operon can produce resistance to multiple unrelated compounds forms the basis for this proposal. Resistance to arsenate and tellurite requires the arsC gene in addition to the genes for the oxyanion pump. The ArsC protein is the first identified member of a new class of reductases. This novel enzyme catalyzes reduction of oxyanions, extending the range of resistance to arsenate and tellurite by transforming those oxyanions into pump substrates. The enzyme uses glutathione as the source of reductant and is postulated to the directly coupled to the oxyanion pump. Thus this system is the bacterial analog of the glutathione S-transferase conjugation system in higher organisms and provides and excellent model system for resistance mechanisms in humans and animals. The overall goal of this project is first, elucidation of the enzymatic mechanism of the ArsC protein, and second, the role of this protein in resistance.