Mechanistic underpinnings of biological oxidative processes: Chemical, computational and genetic analysis of reactions between metalloproteins and redox signalling molecules

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Many chemical messengers trigger cells to respond to environmental changes, both inside and outside the cell. One important messenger is hydrogen peroxide, which has the power to be both toxic and beneficial to cells. For many years, our group studied enzymes called peroxidases that convert hydrogen peroxide to water. We extracted the peroxidases from cells and discovered that they possess many interesting properties, in particular cytochrome c peroxidase (CcP) from yeast. Nonetheless, we realized that we could not fully understand the biological function of these enzymes unless we examined them in their cellular environment. Thus, about six years ago we began investigating the role of CcP in yeast cells and most of the results we obtained so far were totally unpredicted. Importantly, we found that CcP protects cells not by directly decomposing hydrogen peroxide as expected but by sensing its presence and signalling to the cell to produce catalase, an enzyme that is a more efficient hydrogen peroxide scavenger. Now our aim is to unravel at the molecular level how CcP conveys this signal. We have the sophisticated tools to look inside live cells, we can detect how cells chemically modify CcP and other signalling proteins to alter their function or location, we can capture novel proteins that partner with CcP, and we can genetically manipulate yeast cells to remove, mutate or tag any protein of interest. In fact, we have already genetically altered yeast to produce a mutant CcP that does not function as a peroxidase in order to decouple CcP's peroxidase activity from its signalling roles. Yeast contains other enzymes that react with hydrogen peroxide and we will investigate at the molecular level their coordination with CcP in cell signalling and defense. Human cells possess similar signalling pathways as yeast so the knowledge gained will accelerate our understanding of the molecular mechanisms of hydrogen peroxide signalling in health and disease.