6-Nitrotryptophan: A Specific Reaction Product Of Tryptophan Residue In Human Cu, Zn-Sod Treated With Peroxynitrite

Oxidative stress and the HIV-infected brain proteome

Human immunodeficiency virus (HIV) is capable of infiltrating the brain and infecting brain cells. In the years following HIV infection, patients show signs of various levels of neurocognitive problems termed HIV-associated neurocognitive disorders (HAND). Although the introduction of highly active antiretroviral therapy (HAART) has reduced the incidence of HIV-dementia, which is the most severe form of HAND, the milder forms have become more prevalent today due to the increased life expectancy of infected individuals. Pre-HAART era markers such as HIV RNA level, CD4+ count, TNF-α, MCP-1 and M-CSF are not able to clearly distinguish mild from advanced HAND. One promising approach for new biomarker discovery is the identification and quantitation of proteins that are post-translationally modified by oxidative and nitrosative species. The occurrence of oxidative and nitrosative stress in HIV-infected brain, both through the early direct and indirect effects of viral proteins and through the later effect on mitochondrial integrity during apoptosis, is well-established. This review will focus on how the reactive species are produced in the brain after HIV infection, the specific oxidative and nitrosative species that are involved in the post-translational modification of the brain proteome, and the methods that are currently used for the detection of such modified proteins. This review also provides an overview of related research pertaining to oxidative stress-related HAND using cerebrospinal fluid and human brain tissue.

Protein tyrosine nitration: selectivity, physicochemical and biological consequences, denitration, and proteomics methods for the identification of tyrosine-nitrated proteins

Protein tyrosine nitration (PTN) is a post-translational modification occurring under the action of a nitrating agent. Tyrosine is modified in the 3-position of the phenolic ring through the addition of a nitro group (NO2). In the present article, we review the main nitration reactions and elucidate why nitration is not a random chemical process. The particular physical and chemical properties of 3-nitrotyrosine (e.g., pKa, spectrophotometric properties, reduction to aminotyrosine) will be discussed, and the biological consequences of PTN (e.g., modification of enzymatic activity, sensitivity to proteolytic degradation, impact on protein phosphorylation, immunogenicity and implication in disease) will be reviewed. Recent data indicate the possibility of an in vivo denitration process, which will be discussed with respect to the different reaction mechanisms that have been proposed. The second part of this review article focuses on analytical methods to determine this post-translational modification in complex proteomes, which remains a major challenge.

Modification of tryptophan and tryptophan residues in proteins by reactive nitrogen species

Formation of 3-nitrotyrosine by the reaction between reactive nitrogen species (RNS) and tyrosine residues in proteins has been analyzed extensively and it is used widely as a biomarker of pathophysiological and physiological conditions mediated by RNS. In contrast, few studies on the nitration of tryptophan have been reported. This review provides an overview of the studies on tryptophan modifications by RNS and points out the possible importance of its modification in pathophysiological and physiological conditions. Free tryptophan can be modified to several nitrated products (1-, 4-, 5-, 6-, and 7-), 1-N-nitroso product, and several oxidized products by reaction with various RNS, depending on the conditions used. Among them, 1-N-nitrosotryptophan and 6-nitrotryptophan (6-NO(2)Trp) have been found as the abundant products in the reaction with peroxynitrite, and 6-NO(2)Trp has been the most abundant product in the reaction with the peroxidase/hydrogen peroxide/nitrite systems. 6-NO(2)Trp has also been observed as the most abundant nitrated product of the reactions between peroxynitrite or myeloperoxidase/hydrogen peroxide/nitrite and tryptophan residues both in human Cu,Zn-superoxide dismutase and in bovine serum albumin, as well as the reaction of peroxynitrite with myoglobin and hemoglobin. Several oxidized products have also been identified in the modified Cu,Zn-SOD. However, no 1-N-nitrosotryptophan and 1-N-nitrotryptophan has been observed in the proteins reacted with peroxynitrite or the myeloperoxidase/H(2)O(2)/nitrite system. The modification of tryptophan residues in proteins may occur at a more limited number of sites in vivo than that of tyrosine residues, since tryptophan residues are more buried inside proteins and exist less frequently in proteins, generally. However, surface-exposed tryptophan residues tend to participate in the interaction with the other molecules, therefore the modification of those tryptophans may result in modulation of the specific interaction of proteins and enzymes with other molecules.