Factors determining the selectivity of protein tyrosine nitration

Tyrosine nitration is a covalent posttranslational protein modification der ived from the reaction of proteins with nitrating agents. Protein nitration appears to be a selective process since not all tyrosine residues in prote ins or all proteins are nitrated in vivo. To investigate factors that may d etermine the biological selectivity of protein tyrosine nitration, we devel oped an in vitro model consisting of three proteins with similar size but d ifferent three-dimensional structure and tyrosine content. Exposure of ribo nuclease A to putative in vivo nitrating agents revealed preferential nitra tion of tyrosine residue Y-115. Tyrosine residue Y-23 and to a lesser exten t residue Y-20 were preferentially ;nitrated in lysozyme, whereas tyrosine Y-102 was the only residue modified by nitration in phospholipase A(2). Tyr osine Y-115 was the residue modified by nitration after exposure of ribonuc lease A to different nitrating agents: chemically synthesized peroxynitrite , nitric oxide, and superoxide generated by SIN-1 or myeloperoxidase (MPO)/ H2O2 plus nitrite (NO2-) in the presence of bicarbonate/CO2. The nature of the nitrating agent determined in part the protein that would be predominan tly modified by nitration in a mixture of all three proteins. Ribonuclease A was preferentially nitrated upon exposure to MPO/H2O2/NO2-, whereas phosp holipase A(2) was the primary target for nitration upon exposure to peroxyn itrite. The data also suggest that the exposure of the aromatic ring to the surface of the protein, the location of the tyrosine on a loop structure, and its association with a neighboring negative charge are some of the fact ors determining the selectivity of tyrosine nitration In proteins. (C) 1999 Academic Press.