BACKGROUND & AIMS:
:Saccharomyces cerevisiae cells contain three omega-class glutathione transferases with glutaredoxin activity (Gto1, Gto2, and Gto3), in addition to two glutathione transferases (Gtt1 and Gtt2) not classifiable into standard classes. Gto1 is located at the peroxisomes, where it is targeted through a PTS1-type sequence, whereas Gto2 and Gto3 are in the cytosol. Among the GTO genes, GTO2 shows the strongest induction of expression by agents such as diamide, 1-chloro-2,4-dinitrobenzene, tert-butyl hydroperoxide or cadmium, in a manner that is dependent on transcriptional factors Yap1 and/or Msn2/4. Diamide and 1-chloro-2,4-dinitrobenzene (causing depletion of reduced glutathione) also induce expression of GTO1 over basal levels. Phenotypic analyses with single and multiple mutants in the S. cerevisiae glutathione transferase genes show that, in the absence of Gto1 and the two Gtt proteins, cells display increased sensitivity to cadmium. A gto1-null mutant also shows growth defects on oleic acid-based medium, which is indicative of abnormal peroxisomal functions, and altered expression of genes related to sulfur amino acid metabolism. As a consequence, growth of the gto1 mutant is delayed in growth medium without lysine, serine, or threonine, and the mutant cells have low levels of reduced glutathione. The role of Gto1 at the S. cerevisiae peroxisomes could be related to the redox regulation of the Str3 cystathionine beta-lyase protein. This protein is also located at the peroxisomes in S. cerevisiae, where it is involved in transulfuration of cysteine into homocysteine, and requires a conserved cysteine residue for its biological activity.
背景与目标:
: 酿酒酵母细胞包含三种具有谷胱甘肽活性的omega类谷胱甘肽转移酶 (Gto1,Gto2和Gto3),此外还有两种无法归类为标准类的谷胱甘肽转移酶 (Gtt1和Gtt2)。Gto1位于过氧化物酶体,通过PTS1-type序列靶向,而Gto2和Gto3位于细胞质中。在GTO基因中,GTO2以依赖转录因子Yap1和/或Msn2的方式显示出最强的表达诱导作用,例如二酰胺,1-氯-2,4-二硝基苯,叔丁基过氧化氢或镉。/4。二酰胺和1-氯-2,4-二硝基苯 (导致还原型谷胱甘肽耗竭) 也诱导GTO1在基础水平上的表达。用酿酒酵母谷胱甘肽转移酶基因中的单个和多个突变体进行的表型分析表明,在不存在Gto1和两种Gtt蛋白的情况下,细胞对镉的敏感性增强。gto1-null突变体还在油酸基培养基上显示生长缺陷,这表明过氧化物酶体功能异常,以及与硫氨基酸代谢相关的基因表达改变。结果,在没有赖氨酸,丝氨酸或苏氨酸的生长培养基中,gto1突变体的生长被延迟,并且突变细胞的还原型谷胱甘肽水平较低。Gto1在酿酒酵母过氧化物酶体中的作用可能与Str3胱硫醚 β-裂解酶蛋白的氧化还原调节有关。该蛋白也位于酿酒酵母的过氧化物酶体中,参与将半胱氨酸转化为同型半胱氨酸,并且其生物学活性需要保守的半胱氨酸残基。