The Keith Peters Building
Achieving Redox Signalling specificity through Spatiotemporal and Chemical approaches
Redox signalling is a form of signal transduction that starts with the production of hydrogen peroxide and proceeds through the reversible oxidation of cysteine-thiol side-chains of proteins. It is clear that redox signalling leads only to oxidation of very specific proteins, but this is in apparent conflict with the chemical simplicity of H2O2. Furthermore, most cysteines found to play a role in redox signalling have a relatively low reactivity to H2O2 compared to the catalytic cysteines in dedicated H2O2 scavenging enzymes. It is therefore not surprising that understanding how specificity and reactivity of Cysteine oxidation is being achieved in redox signalling is arguably the biggest question in the field. Recent studies have described cases in which Peroxiredoxins, dedicated H2O2 scavengers, after oxidation can partake in a redox relay reaction to oxidise cysteines in a client protein. We have undertaken extensive quantitative mass-spectrometry studies that suggest that 1) Peroxiredoxin mediated redox relay is a wide-spread phenomenon, 2) Each of the five human 2-Cys peroxiredoxins have a preferred set of targets for the redox relay reaction and 3) redox relay can take place by two distinct molecular mechanisms that could aid in the cellular response to different levels of H2O2.
Another layer of specificity in redox signalling that has been proposed is through spatiotemproral control of H2O2 production by for instance mitochondria, but good model systems to study this have been lacking. Cell polarization requires the dynamic regulation of signaling cascades in both time and space, making it an attractive model to study localized, subcellular (redox)signalling. We take advantage of this and use the C. elegans early embryo, one of the most-studied systems for cell polarization, to analyze the spatiotemporal regulation of redox signaling. We find that, coinciding with polarization, a subgroup of mitochondria relocates to the cell membrane at the site of symmetry breaking. After this, mitochondria become highly motile and localize closely to the posterior cortex of the embryo. An ultrasensitive H2O2 -specific sensor that we optimized for live imaging in C. elegans shows that mitochondrial relocation to the cell membrane is accompanied by a striking increase in cortical H2O2 –levels. Furthermore, mitochondrial H2O2 directly influences polarization, since compounds that alter mitochondrial H2O2 -production affect symmetry breaking and maximal polarization. Our observations show that redox signalling can indeed be initiated by the local production of H2O2, and that cell polarization is regulated by redox signalling.
Collectively these data suggest that redox signalling specificity can be regulated both by differences in the chemical properties of peroxiredoxin-mediated redox-relay targets and by spatiotemporal control of H2O2 production.