In addition to be involved in cell and tissue damage, oxidants are presently recognized to participate in signaling mechanisms. Part of the redox signaling responses occur through reversible modifications of cysteine residues in proteins. For instance, hydrogen peroxide reacts directly with specific cysteine thiols (-SH) in proteins to form sulfenic acid derivatives (-SOH) and these processes have been extensively studied in recent years. In contrast, nitric oxide does not react directly with protein thiols to produce nitrosothiol proteins (-SNO), a process known as S-nitrosation1. Nevertheless, a number of recent reports on the S-nitrosoproteome established the widespread occurrence of protein S-nitrosation in cells and tissues. Not surprisingly, protein S-nitrosation has been proposed to control a number of physiological processes, such as vascular homeostasis, autophagy and the innate immune response. Likewise, dysregulation of protein S-nitrosation has been associated with several diseases, including neurodegenerative disorders, various cancers, and diabetes. However, the mechanisms by which S-nitrosated proteins are produced in vivo remain debatable. Till recently, the mechanisms proposed involved either transnitrosation reactions of low molecular weight thiols, such as nitrosoglutathione and nitrosocysteine with thiol proteins, or redox reactions between thiols with metalloproteins and with nitric oxide metabolites, such as trioxide of dinitrogen and nitrogen dioxide. Although all these mechanisms may operate in vivo, each of them has, apparently, kinetic constrains that are difficult to reconcile with the physiological and pathological concentrations of nitric oxide metabolites and with the selectivity expected for signaling mechanisms. An attractive hypothesis worth to explore is the possibility of protein S-nitrosation occurring through catalysis by dinitrosyl iron complexes. These complexes have been long known in the literature because they are universally detectable by EPR in cells and tissues under conditions of nitric oxide overproduction. However, their chemical nature remains unknown and their biochemical properties have been little explored. In this context, it is our aim to investigate the kinetics and mechanisms of the S-nitrosation of peroxiredoxins (Prxs), and other thiol proteins by low and high molecular weight iron dinitrosyl complexes in comparison with low molecular weight nitrosothiols. Prxs are interesting targets to examine because they react rapidly with hydrogen peroxide and may provide a route for the crosstalk between reactive oxygen species and reactive nitrogen species. In addition, Prxs have been proposed to transnitrosate other thiol proteins. In parallel, we intend to design and test approaches to characterize the high molecular weight iron-dinitrosyl complexes detectable in cells and tissues overproducing nitric oxide.
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