S-Nitrosylation Is Emerging as a Specific and Fundamental Posttranslational Protein Modification: Head-to-Head Comparison with O-Phosphorylation

Nitric oxide (NO) is a free-radical product of mammalian cell metabolism that plays diverse and important roles in the regulation of cell function. Biological actions of NO arise as a direct consequence of chemical reactions between NO or NO-derived species and protein targets. Reactions of NO with transition metals in target proteins have garnered the most attention to date as the principal mechanism of NO signaling; nonetheless, S-nitrosylation of protein Cys residues is rapidly moving to center stage in importance. In general, however, there has been a delay in adequate appreciation of the role of S-nitrosylation in biological signaling by NO. This lag is attributed to a poor understanding of the basis for selective targeting of NO to particular thiols, and methodological limitations in accurately quantifying this modification--recent breakthroughs in concepts and methods diminish these barriers. Here, we consider the wheres and whys of protein S-nitrosylation and its basis for specificity. Protein S-nitrosylation potentially represents a ubiquitous and fundamental mechanism for posttranslational control of protein activity on a par with that of O-phosphorylation.