Sumner Edward R, Shanmuganathan Anupama, Sideri Theodora C, Willetts Sylvia A, Houghton John E, Avery Simon V
School of Biology, Institute of Genetics, University of Nottingham, University Park, Nottingham NG7 2RD, UK.
Department of Biology, Georgia State University, University Plaza, Atlanta, GA 30303, USA.
Microbiology (Reading). 2005 Jun;151(Pt 6):1939-1948. doi: 10.1099/mic.0.27945-0.
Oxidative damage in microbial cells occurs during exposure to the toxic metal chromium, but it is not certain whether such oxidation accounts for the toxicity of Cr. Here, a Saccharomyces cerevisiae sod1Delta mutant (defective for the Cu,Zn-superoxide dismutase) was found to be hypersensitive to Cr(VI) toxicity under aerobic conditions, but this phenotype was suppressed under anaerobic conditions. Studies with cells expressing a Sod1p variant (Sod1(H46C)) showed that the superoxide dismutase activity rather than the metal-binding function of Sod1p was required for Cr resistance. To help identify the macromolecular target(s) of Cr-dependent oxidative damage, cells deficient for the reduction of phospholipid hydroperoxides (gpx3Delta and gpx1Delta/gpx2Delta/gpx3Delta) and for the repair of DNA oxidation (ogg1Delta and rad30Delta/ogg1Delta) were tested, but were found not to be Cr-sensitive. In contrast, S. cerevisiae msraDelta (mxr1Delta) and msrbDelta (ycl033cDelta) mutants defective for peptide methionine sulfoxide reductase (MSR) activity exhibited a Cr sensitivity phenotype, and cells overexpressing these enzymes were Cr-resistant. Overexpression of MSRs also suppressed the Cr sensitivity of sod1Delta cells. The inference that protein oxidation is a primary mechanism of Cr toxicity was corroborated by an observed approximately 20-fold increase in the cellular levels of protein carbonyls within 30 min of Cr exposure. Carbonylation was not distributed evenly among the expressed proteins of the cells; certain glycolytic enzymes and heat-shock proteins were specifically targeted by Cr-dependent oxidative damage. This study establishes an oxidative mode of Cr toxicity in S. cerevisiae, which primarily involves oxidative damage to cellular proteins.
微生物细胞在接触有毒金属铬的过程中会发生氧化损伤，但这种氧化是否是铬毒性的原因尚不确定。在此，发现酿酒酵母sod1Δ突变体（铜锌超氧化物歧化酶缺陷）在有氧条件下对Cr(VI)毒性高度敏感，但在厌氧条件下该表型受到抑制。对表达Sod1p变体（Sod1(H46C)）的细胞的研究表明，抗铬需要超氧化物歧化酶活性而非Sod1p的金属结合功能。为了帮助确定铬依赖性氧化损伤的大分子靶点，测试了缺乏磷脂氢过氧化物还原能力（gpx3Δ和gpx1Δ/gpx2Δ/gpx3Δ）以及DNA氧化修复能力（ogg1Δ和rad30Δ/ogg1Δ）的细胞，但发现它们对铬不敏感。相反，缺乏肽甲硫氨酸亚砜还原酶（MSR）活性的酿酒酵母msraΔ（mxr1Δ）和msrbΔ（ycl033cΔ）突变体表现出铬敏感表型，而过表达这些酶的细胞具有抗铬性。MSR的过表达也抑制了sod1Δ细胞的铬敏感性。在接触铬30分钟内，细胞内蛋白质羰基水平观察到约20倍的增加，这证实了蛋白质氧化是铬毒性的主要机制这一推断。羰基化在细胞表达的蛋白质中分布不均；某些糖酵解酶和热休克蛋白是铬依赖性氧化损伤的特异性靶点。本研究确立了酿酒酵母中铬毒性的氧化模式，其主要涉及对细胞蛋白质的氧化损伤。
