Expression of human A4V mutant Cu,Zn superoxide dismutase in Schizosaccharomyces pombe: investigations of its toxic properties.

Cu,Zn superoxide dismutase (SOD1) is an antioxidant enzyme that catalyzes the removal of superoxide radicals generated in various biological oxidations. Amyotrophic lateral sclerosis (ALS) is one of the most common neurodegenerative disorders, occurring in families (FALS) and sporadically (SALS). FALS and SALS are distinguishable genetically but not clinically. More than 100 point mutations in the human SOD 1 gene have been identified that cause FALS. In order to determine the effects of mutant SOD protein, we first cloned wild-type and A4V mutant human SOD1 into Schizosaccharomyces pombe. This study shows viabilities and some antioxidant properties including SOD, catalase, proteasomal activity, and protein carbonyl levels of transformants in SOD1 deleted strain (MN415); and its parental strain (JY741) at different stress conditions. There was no more oxidative damage in the human mutant SOD carrying the transformant strain compared with other strains. These results may help to explain whether ALS progresses as a consequence of cellular oxidative damage.

Intracellular scavenging activity of Trolox (6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid) in the fission yeast, Schizosaccharomyces pombe.

The ability of Trolox (6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid), a water-soluble vitamin E analogue, to prevent oxidative damages is well characterized, but the mechanisms underlying it remain unclear. The protective effect of Trolox pre-treatment on H(2)O(2)-induced toxicity might be attributed to the decreased cellular permeability to H(2)O(2) or in vitro scavenging activity of Trolox, induction of antioxidant enzymes or the direct scavenging activity of Trolox. The results obtained rule out the first and second possibilities and intracellular scavenging activity was found to be the mechanism whereby Trolox confers protection. This was confirmed by measuring protein oxidation (levels), and the observed decrease in proteasomal activity indicated that the decrease in protein carbonyls was due to Trolox scavenging activity rather than proteasome activation. In conclusion, the intracellular scavenging activity of Trolox is a key protective mechanism against H(2)O(2). These findings obtained in Schizosaccharomyces pombe, a good model organism for eukaryotic cells, can be used as standard protocols for investigating the antioxidant activity of pure or complex potential antioxidants.

The effect of superoxide dismutase deficiency on zinc toxicity in Schizosaccharomyces pombe.

Zinc is a metal which is a cofactor in many enzymes and a structural element in zinc finger motifs those are important in relation between DNA and regulator proteins. Little is known about uptake, distribution, toxicity and detoxification of zinc ions in cells. In this study, zinc toxicity and detoxification levels have been compared in wild type and Cu/Zn superoxide dismutase mutant (sod1Delta) cells of the fission yeast Schizosaccharomyces pombe. We evaluated the toxic levels of zinc, total zinc content, lipid peroxidation levels and catalase activities for both strains which were grown in medium containing different concentrations of zinc. sod1Delta mutant showed important growth retardation and has higher lipid peroxidation and catalase activities than wild type. Cu/Zn superoxide dismutase (SOD1) activity of wild type cells was markedly increased when they were treated with elevated levels of zinc. SOD1 mRNA level also significantly increased when the cells treated with higher concentrations of zinc. These results indicate that the mutant cells were more sensitive to zinc stress and seemed to have more oxidative intracellular environment than wild type cells. Our results support the idea that superoxide dismutase is an important factor for zinc detoxification in eukaryotes.

The 3' terminal sequence of the inosine monophosphate dehydrogenase gene encodes an active domain in the yeast Schizosaccharomyces pombe

The gua1 gene encoding inosine monophosphate dehydrogenase (IMPDH), which catalyses the first step in de novo biosynthesis of guanosine monophosphate (GMP), was cloned in the yeast Schizosaccharomyces pombe by functional complementation of a gua1ura4-D18 mutant strain from a S. pombe DNA genomic library. Complementation analysis revealed a 1.2 kb fragment which segregation analysis confirmed did not code for a suppressor gene. Only 446 nucleotides of the gua1 gene encoding the IMPDH C-terminal residues were found within this 1.2 kb sequence (GenBank, AJ293460). The comparison of this wild-type fragment with the same fragment from the gua1ura4-D18 mutant revealed that there was a point mutation at position 1261 (guanine -> adenine) from the 5' end, corresponding to the amino acid residue 421 (glycine -> serine) of the enzyme. Dot and Northern analyses showed that the gua1 gene was expressed in transformants as well as in the wild-type and the gua1ura4-D18 mutant, but enzyme activity was only detected in wild-type and transformant cells. It seems likely that a 446 bp fragment from the 3' end of the gua1 gene abolished the point mutation in the mutant strain, suggesting that this fragment participates in the sequences encoding the active domain of IMPDH in S. pombe.