Biomedical subjects

Shingo Izawa

Publications and source records attributed to Shingo Izawa.

21 records · Page 2Linked to original sources

PubMed2004

Identification of thermostable glyoxalase I in the fission yeast Schizosaccharomyces pombe.

Glyoxalase I is a ubiquitous enzyme that detoxifies methylglyoxal, which is derived from glycolysis but inhibits the growth of cells from microorganisms to mammals. Here, the structural gene for glyoxalase I ( glo1(+)) from the fission yeast Schizosaccharomyces pombe was identified. Disruption of glo1(+) enhanced susceptibility to methylglyoxal, while expression of glo1(+) in a Delta glo1 mutant of Saccharomyces cerevisiae restored tolerance to this aldehyde. The glo1(+) gene product was purified. The glyoxalase I of S. pombe was a monomeric enzyme with a molecular weight of 34000 and the k(cat)/ K(m) value for methylglyoxal was 4.3 x 10(7) M(-1) x min(-1). Treatment of purified enzyme with EDTA in imidazole buffer completely abolished enzyme activity, whereas the EDTA-treated enzyme was reactivated by several divalent metal ions, such as Zn(2+), Co(2+), Ni(2+) and Mn(2+). The glyoxalase I of S. pombe exhibited fairly high thermal stability, and almost 100% activity was retained after incubating the enzyme at 60 degrees C for 4 h.

Base Sequence↗

PubMed2004

Deficiency in the glycerol channel Fps1p confers increased freeze tolerance to yeast cells: application of the fps1delta mutant to frozen dough technology.

Intracellular glycerol content affects the freeze-thaw stress tolerance of Saccharomyces cerevisiae. We have recently reported that intracellular-glycerol-enriched cells cultured in glycerol medium acquire tolerance to freeze stress and retain high leavening ability even in dough after frozen storage [Izawa et al. (2004) Appl Microbiol Biotechnol http://dx.doi.org/10.1007/s00253-004-1624-4]. A deletion mutant of the FPS1 gene, which encodes a glycerol channel, accumulates glycerol inside the cell without an exogenous supply of glycerol into the medium. We found that the fps1delta cells acquired tolerance to freeze stress and retained high leavening ability in dough after frozen storage for 7 days. These results suggest that the fps1delta mutant is a useful strain for developing better frozen-dough with a commercial advantage.

Bread↗

PubMed2004

Activity of the Yap1 transcription factor in Saccharomyces cerevisiae is modulated by methylglyoxal, a metabolite derived from glycolysis.

Methylglyoxal (MG) is synthesized during glycolysis, although it inhibits cell growth in all types of organisms. Hence, it has long been asked why such a toxic metabolite is synthesized in vivo. Glyoxalase I is a major enzyme detoxifying MG. Here we show that the Yap1 transcription factor, which is critical for the oxidative-stress response in Saccharomyces cerevisiae, is constitutively concentrated in the nucleus and activates the expression of its target genes in a glyoxalase I-deficient mutant. Yap1 contains six cysteine residues in two cysteine-rich domains (CRDs), i.e., three cysteine residues clustering near the N terminus (n-CRD) and the remaining three cysteine residues near the C terminus (c-CRD). We reveal that any of the three cysteine residues in the c-CRD is sufficient for MG to allow Yap1 to translocate into the nucleus and to activate the expression of its target gene. A Yap1 mutant possessing only one cysteine residue in the c-CRD but no cysteine in the n-CRD and deletion of the basic leucine zipper domain can concentrate in the nucleus with MG treatment. However, substitution of all the cysteine residues in Yap1 abolishes the ability of this transcription factor to concentrate in the nucleus following MG treatment. The redox status of Yap1 is substantially unchanged, and protein(s) interaction with Yap1 through disulfide bond is hardly detected in cells treated with MG. Collectively, neither intermolecular nor intramolecular disulfide bond formation seems to be involved in Yap1 activation by MG. Moreover, we show that nucleocytoplasmic localization of Yap1 closely correlates with growth phase and intracellular MG level. We propose a novel regulatory pathway underlying Yap1 activation by a natural metabolite in the cell.

Gene Expression Regulation, Fungal↗