Expression of Ovotransferrin Enhances Tolerance of Yeast Cells toward Oxidative Stress

Recently, we found that ovotransferrin (OTf) undergoes distinct self-cleavage in a redox-dependent process and exhibited in vitro superoxide dismutase (SOD)-like activity. In this study, we explore that the expression of OTf confers high tolerance to oxidative stress in yeast cells. The OTf gene was cloned into the vector pPICZB and was successfully expressed in methylotrophic yeast, Pichia pastoris KM71H. There was no growth difference between the non-transformed strain and recombinant strains harboring a mock vector (pPICZB) or the OTf gene carrying a vector (OTf-pPICZB). Intracellularly expressed OTf was found to undergo self cleavage, producing a major fragment of 15 kDa, which corresponded to the disulfide kringle domain of the N-terminal lobe. The yeast OTf transformants exhibited strong tolerance to oxidative stress induced by either hydrogen peroxide (H2O2) or diethyl maleate (DEM). Further, OTf transformants showed higher intracellular reducing capacity and enhanced cytosolic reductase activity. This study is the first to describe the ability of OTf to confer in vivo antioxidative stress function within a complicated milieu of eukaryotic cells and provide novel insights for the potential of the OTf gene for molecular breeding of industrial yeast strains with high tolerance to oxidative stress.