Biological redox chemistry underlying nitric oxide and hydrogen peroxide signaling

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We are investigating how small, redox-active molecules such as hydrogen peroxide (H2O2) and nitric oxide (NO) interact with metalloproteins and other biomolecules to control the functioning of cells. Excess H2O2 can harm cells and cause programmed cell death (apoptosis) involving the heme protein, cytochrome c. We are interested in the detailed chemical processes that trigger this event since an ability to control apoptosis is highly desirable in the treatment of stroke and cancer. Under normal conditions, cellular H2O2 levels are tightly controlled. Because of its ease of genetic manipulation, we are using baker's yeast in our search for new molecular mechanisms of H2O2 sensing and signaling. Our focus is the heme enzyme, cytochrome c peroxidase (CCP), which can detoxifiy H2O2 by catalyzing its reduction to H2O. We are investigating genetically modified yeast strains that produce CCP mutants or no CCP at all. We also study purified CCP and its mutants in vitro to better understand its mode of action in vivo. The goal of this work is to obtain chemical insight into how organisms respond rapidly to redox challenges that occur in an oxygen rich environment. Oxidative stress is a major contributing factor in aging and in age-related diseases.Nitric oxide (NO) influences key biological functions such as blood flow, neuronal signaling and the immune response. We would like to understand how NO chemically modifies proteins and hormones, which can have profound effects on their mode of action. For example, reversible S-nitrosation of protein thiols is a major form of cell signaling, and research in our laboratory focuses on metal-catalyzed processes that promote NO-transfer between thiols. We are also probing the chemical reactions of the one-electron reduction product of NO, nitroxyl (HNO). The proposed studies will increase our knowledge of the bioinorganic chemistry of NO, which is critical in understanding the molecular underpinnings of cardiovascular disease and neurodegeneration.