S-glutathionylation of fructose-1,6-bisphosphate aldolase confers nitrosative stress tolerance on yeast cells via a metabolic switch

Nitric oxide as a signaling molecule exerts cytotoxicity known as nitrosative stress at its excess concentrations. In the yeast Saccharomyces cerevisiae, the cellular responses to nitrosative stress and their molecular mechanisms are not fully understood. Here, focusing on the posttranslational modifications that are associated with nitrosative stress response, we show that nitrosative stress increased the protein S-glutathionylation level in yeast cells. Our proteomic and immunochemical analyses demonstrated that the fructose-1,6-bisphosphate aldolase Fba1 underwent S-glutathionylation at Cys112 in response to nitrosative stress. The enzyme assay using a recombinant Fba1 demonstrated that S-glutathionylation at Cys112 inhibited the Fba1 activity. Moreover, we revealed that the cytosolic glutaredoxin Grx1 reduced S-glutathionylation of Fba1 and then recovered its activity. The intracellular contents of fructose-1,6-bisphosphate and 6-phosphogluconate, which are a substrate of Fba1 and an intermediate of the pentose phosphate pathway (PPP), respectively, were increased in response to nitrosative stress, suggesting that the metabolic flow was switched from glycolysis to PPP. The cellular level of NADPH, which is produced in PPP and functions as a reducing force for nitric oxide detoxifying enzymes, was also elevated under nitrosative stress conditions, but this increase was canceled by the amino acid substitution of Cys112 to Ser in Fba1. Furthermore, the viability of yeast cells expressing Cys112Ser-Fba1 was significantly lower than that of the wild-type cells under nitrosative stress conditions. These results indicate that the inhibition of Fba1 by its S-glutathionylation changes metabolism from glycolysis to PPP to increase NADPH production, leading to nitrosative stress tolerance in yeast cells.