Expression of the Laccase Gene from a White Rot Fungus in Pichia pastoris Can Enhance the Resistance of This Yeast to H 2 O 2 -Mediated Oxidative Stress by Stimulating the Glutathione-Based Antioxidative System

Abstract

Laccase is a copper-containing polyphenol oxidase that has great potential in industrial and biotechnological applications. Previous research has suggested that fungal laccase may be involved in the defense against oxidative stress, but there is little direct evidence supporting this hypothesis, and the mechanism by which laccase protects cells from oxidative stress also remains unclear. Here, we report that the expression of the laccase gene from white rot fungus in Pichia pastoris can significantly enhance the resistance of yeast to H ₂ O ₂ -mediated oxidative stress. The expression of laccase in yeast was found to confer a strong ability to scavenge intracellular H ₂ O ₂ and to protect cells from lipid oxidative damage. The mechanism by which laccase gene expression increases resistance to oxidative stress was then investigated further. We found that laccase gene expression in Pichia pastoris could increase the level of glutathione-based antioxidative activity, including the intracellular glutathione levels and the enzymatic activity of glutathione peroxidase, glutathione reductase, and γ-glutamylcysteine synthetase. The transcription of the laccase gene in Pichia pastoris was found to be enhanced by the oxidative stress caused by exogenous H ₂ O ₂ . The stimulation of laccase gene expression in response to exogenous H ₂ O ₂ stress further contributed to the transcriptional induction of the genes involved in the glutathione-dependent antioxidative system, including PpYAP1 , PpGPX1 , PpPMP20 , PpGLR1 , and PpGSH1 . Taken together, these results suggest that the expression of the laccase gene in Pichia pastoris can enhance the resistance of yeast to H ₂ O ₂ -mediated oxidative stress by stimulating the glutathione-based antioxidative system to protect the cell from oxidative damage.