Schmitz, H. | bioRxiv Science

bioRxiv2022

p66Shc is an apoptotic rheostat whose targeted ROS inhibition improves MI outcomes

p66Shc is an oxidoreductase that responds to cell stress by translocating to mitochondria, where p66Shc produces pro-apoptotic reactive oxygen species (ROS). This study identifies ROS-active p66Shc as a monomer that produces superoxide anion independent of metal ions, inhibits cytochrome c peroxidase, and is regulated by environmental condition-induced structural changes. p66Shc anti-apoptotic functions, including: cytochrome c reduction, increased electron transport chain activity, and caspase cascade inhibition were also discovered. This study also demonstrates that p66Shc is a stress-dependent rheostat of apoptosis, regulated by p66Shc-mortalin complexes. These complexes decrease pro-apoptotic ROS production, without blocking p66Shc-mediated cytochrome c reduction. However, stress disrupts p66Shc-mortalin interactions, promoting apoptosis. Tipping p66Shcs apoptotic balance toward anti-apoptotic functions by genetic knockdown or p66Shc-selective ROS inhibition decreased pro-apoptotic effects and improved outcomes in zebrafish myocardial infarction models, representing a potential new myocardial infarction treatment with promising results.

biochemistry↗

bioRxiv2020

Single molecule dynamics at a bacterial replication fork after nutritional downshift

Replication forks must respond to changes in nutrient conditions, especially in bacterial cells. By investigating the single molecule dynamics of replicative helicase DnaC, DNA primase DnaG, and of lagging strand polymerase DnaE in the model bacterium Bacillus subtilis in response to transient replication blocks due to DNA damage, to inhibition of the replicative polymerase, or to downshift of serine availability, we show that proteins react differentially to the stress conditions. DnaG appears to be recruited to the forks by a diffusion and capture mechanism, becomes more statically associated after arrest of polymerase PolC, but binds much less often after fork blocks due to DNA damage or to nutritional downshift. These results indicate that binding of the alarmone ppGpp due to the stringent response prevents DnaG from binding to forks rather than blocking bound primase. Dissimilar behaviour of DnaG and of DnaE suggest that both proteins are recruited independently to the forks, rather than jointly. Turnover of all three proteins was increased during replication block after nutritional downshift, different from the situation due to DNA damage or polymerase inhibition, showing high plasticity of forks in response to different stress conditions. Forks persisted during all stress conditions, apparently ensuring rapid return to replication extension.

cell biology↗