Protein nitrotryptophan: Formation, significance and identification

Reactive nitrogen species are formed during a variety of disease states and have been shown to modify several amino acids on proteins. To date, the majority of research in this area has focused on the nitration of tyrosine residues to form 3-nitrotyrosine. However, emerging evidence suggests that another modification, nitration of tryptophan residues, to form nitrotryptophan (NO2-Trp), may also play a significant role in the biology of nitrosative stress. This review takes an in-depth look at NO2-Trp, presenting the current research about its formation, prevalence and biological significance, as well as the methods used to identify NO2-Trp-modified proteins. Although more research is needed to understand the full biological role of NO2-Trp, the data presented herein suggest a contribution to nitrosative stress-induced cell dysregulation and perhaps even in physiological cell processes.

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► Emerging evidence demonstrates that nitration of tryptophan residues occurs in proteins.
► Newly developed methods are enhancing our ability to detect these modifications both in vitro and in vivo.
► We review the current literature on the formation, significance, and identification of protein nitrotryptophan.