Abstract

Saccharomyces cerevisiae is a facultative anaerobic organism that grows well under both aerobic and hypoxic conditions in media containing abundant fermentable nutrients such as glucose. In order to deeply understand the physiological dependence of S. cerevisiae on aeration, we checked endoplasmic reticulum (ER)-stress status by monitoring the splicing of HAC1 mRNA, which is promoted by the ER stress-sensor protein, Ire1. HAC1-mRNA splicing that was caused by conventional ER-stressing agents, including low concentrations of dithiothreitol (DTT), was more potent in hypoxic cultures than in aerated cultures. Moreover, growth retardation was observed by adding low-dose DTT into hypoxic cultures of ire1Δ cells. Unexpectedly, aeration mitigated ER stress and DTT-induced impairment of ER oxidative protein folding even when mitochondrial respiration was halted by the ρo mutation. An ER-located protein Ero1 is known to directly consume molecular oxygen to initiate the ER protein oxidation cascade, which promotes oxidative protein folding of ER client proteins. Our further study using ero1-mutant strains suggested that, in addition to mitochondrial respiration, this Ero1-medaited reaction contributes to mitigation of ER stress by molecular oxygen. Taken together, here we demonstrate a scenario in which aeration acts beneficially on S. cerevisiae cells even under fermentative conditions.

Highlights

  • The endoplasmic reticulum (ER) is a flat or tubular-shaped membranous sac, which facilitates the folding and maturation of proteins that are subsequently transported to the cell surface or other organelles

  • At the beginning of this study, we examined how aerobic shaking of cultures affects the splicing of HAC1 mRNA, which represents ER-stressing status, in S. cerevisiae cells

  • The HAC1-mRNA splicing that was weakly induced by low-dose DTT, low-dose tunicamycin, or ethanol was boosted when cells were cultured under the static condition (Fig. 1)

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Summary

Introduction

The endoplasmic reticulum (ER) is a flat or tubular-shaped membranous sac, which facilitates the folding and maturation of proteins that are subsequently transported to the cell surface or other organelles. Protein folding in the ER frequently accompanies formation of the disulfide bond between two cysteine residues, and is called oxidative protein folding [1]. While protein disulfideisomerases (PDIs) directly promote the oxidative folding of ER client proteins, Ero mediates the oxidation of PDI [1, 2]. Ero initiates an ER oxidation cascade that contributes to the disulfide-bond formation and oxidative folding of ER client proteins. Proteins are subjected to the N-linked glycosylation in the ER. Dysfunction of the ER is tightly linked to accumulation of unfolded proteins in the ER, and is known as ER stress

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