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:
:酿酒酵母细胞除含有两种无法分类为标准类别的谷胱甘肽转移酶(Gtt1和Gtt2)外,还包含三种具有谷胱甘肽毒素活性的欧米茄类谷胱甘肽转移酶(Gto1,Gto2和Gto3)。 Gto1位于过氧化物酶体,通过PTS1型序列被靶向,而Gto2和Gto3在细胞质中。在GTO基因中,GTO2以最依赖转录因子Yap1和/或Msn2 /的方式显示出最强的诱导作用,例如二酰胺,1-氯-2,4-二硝基苯,叔丁基氢过氧化物或镉。 4,二酰胺和1-氯-2,4-二硝基苯(导致减少的还原型谷胱甘肽)也诱导GTO1表达超过基础水平。对酿酒酵母谷胱甘肽转移酶基因中单个和多个突变体的表型分析表明,在缺少Gto1和两个Gtt蛋白的情况下,细胞对镉的敏感性增加。 gto1-null突变体还在基于油酸的培养基上显示出生长缺陷,这表明过氧化物酶体功能异常,并且改变了与硫氨基酸代谢相关的基因的表达。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,并且该突变体细胞具有低水平的还原型谷胱甘肽。 Gto1在酿酒酵母过氧化物酶体中的作用可能与Str3胱硫醚β-裂合酶蛋白的氧化还原调节有关。该蛋白也位于酿酒酵母中的过氧化物酶体处,在其中它参与半胱氨酸转硫为高半胱氨酸,并且需要保守的半胱氨酸残基才能发挥其生物学活性。