Hydrogen peroxide (H2O2) plays important roles in cellular signaling, yet nonetheless is toxic at higher concentrations. Surprisingly, the mechanism(s) of cellular H2O2 toxicity remain poorly understood. Here, we reveal an important role for mitochondrial 1‐Cys peroxiredoxin from budding yeast, Prx1, in regulating H2O2‐induced cell death. We show that Prx1 efficiently transfers oxidative equivalents from H2O2 to the mitochondrial glutathione pool. Deletion of PRX1 abrogates glutathione oxidation and leads to a cytosolic adaptive response involving upregulation of the catalase, Ctt1. Both of these effects contribute to improved cell viability following an acute H2O2 challenge. By replacing PRX1 with natural and engineered peroxiredoxin variants, we could predictably induce widely differing matrix glutathione responses to H2O2. Therefore, we demonstrated a key role for matrix glutathione oxidation in driving H2O2‐induced cell death. Finally, we reveal that hyperoxidation of Prx1 serves as a switch‐off mechanism to limit oxidation of matrix glutathione at high H2O2 concentrations. This enables yeast cells to strike a fine balance between H2O2 removal and limitation of matrix glutathione oxidation.

Mitochondria shed their SPOTs Outer mitochondrial membrane (OMM) function is essential for cellular health. How mitochondria respond to naturally occurring OMM stress is unknown. Li et al . show that, upon infection with the human parasite Toxoplasma gondii , mitochondria shed large structures positive for OMM (SPOTs). SPOT formation required the parasite effector TgMAF1 and its interaction with the host mitochondrial receptor TOM70 and translocase SAM50. TOM70-dependent SPOT formation mediated a depletion of mitochondrial proteins and optimal parasite growth. SPOT-like structures also formed after OMM perturbations independently of infection. Thus, membrane remodeling is a feature of cellular responses to OMM stress that Toxoplasma hijacks during infection. —SMH

Background The mitochondrial intermembrane space (IMS) is home to proteins fulfilling numerous essential cellular processes, particularly in metabolism and mitochondrial function. All IMS proteins are nuclear encoded and synthesized in the cytosol and must therefore be correctly targeted and transported to the IMS, either through mitochondrial targeting sequences or conserved cysteines and the mitochondrial disulfide relay system. The mitochondrial oxidoreductase MIA40, which catalyzes disulfide formation in the IMS, is imported by the combined action of the protein AIFM1 and MIA40 itself. Here, we characterized the function of the conserved highly negatively charged C-terminal region of human MIA40. Results We demonstrate that the C-terminal region is critical during posttranslational mitochondrial import of MIA40, but is dispensable for MIA40 redox function in vitro and in intact cells. The C-terminal negatively charged region of MIA40 slowed import into mitochondria, which occurred with a half-time as slow as 90 min. During this time, the MIA40 precursor persisted in the cytosol in an unfolded state, and the C-terminal negatively charged region served in protecting MIA40 from proteasomal degradation. This stabilizing property of the MIA40 C-terminal region could also be conferred to a different mitochondrial precursor protein, COX19. Conclusions Our data suggest that the MIA40 precursor contains the stabilizing information to allow for postranslational import of sufficient amounts of MIA40 for full functionality of the essential disulfide relay. We thereby provide for the first time mechanistic insights into the determinants controlling cytosolic surveillance of IMS precursor proteins.

The mitochondrial intermembrane space protein AIFM1 has been reported to mediate the import of MIA40/CHCHD4, which forms the import receptor in the mitochondrial disulfide relay. Here, we demonstrate that AIFM1 and MIA40/CHCHD4 cooperate beyond this MIA40/CHCHD4 import. We show that AIFM1 and MIA40/CHCHD4 form a stable long‐lived complex in vitro, in different cell lines, and in tissues. In HEK293 cells lacking AIFM1, levels of MIA40 are unchanged, but the protein is present in the monomeric form. Monomeric MIA40 neither efficiently interacts with nor mediates the import of specific substrates. The import defect is especially severe for NDUFS5, a subunit of complex I of the respiratory chain. As a consequence, NDUFS5 accumulates in the cytosol and undergoes rapid proteasomal degradation. Lack of mitochondrial NDUFS5 in turn results in stalling of complex I assembly. Collectively, we demonstrate that AIFM1 serves two overlapping functions: importing MIA40/CHCHD4 and constituting an integral part of the disulfide relay that ensures efficient interaction of MIA40/CHCHD4 with specific substrates.

Hand hygiene for children is crucial to keep them healthy. The purpose of the study was to evaluate the effects of two educational initiatives on "handwashing effectiveness (HWE)." A randomized controlled trial was carried out during April/June 2016, and 96 primary school students were randomly assigned to Group I receiving education with fluorescent gel; Group II receiving interactive education or control group continuing its normal education. Evaluation was made by scoring the fluorescent areas on the hands with photographs. There were significant differences in handwashing scores between preprogram and postprogram for all areas in only Group II ( p < .05). HWE increased from 17.9% to 18.4% in Group I, from 15.4% to 37.7% in Group II, and from 35.5% to 35.8% in control group. Only concretization with fluorescent gel is not a sufficiently strong motivator for increasing HWE. New techniques should be integrated into the training programs for children.