Snitrosation

Snitrosation, or S-nitrosation, is a chemical modification in which a nitroso group (-NO) is added to a thiol (-SH) to form an S-nitrosothiol (RS-NO). This modification can occur on low-molecular-weight thiols and on cysteine residues within proteins, and it is a key mechanism of redox-based signaling in biology.

The reaction often involves nitrosating agents such as the nitrosonium ion (NO+), which can be generated from nitrite (NO2−) under acidic conditions or via metal-catalyzed processes. S-nitrosation can happen by direct nitrosylation of a thiolate (RS−) or through transnitrosation, where the nitroso group is transferred from one S-nitrosothiol to another thiol. The process is reversible; cellular reductants such as glutathione and thioredoxin can cleave the S−NO bond, restoring the thiol.

Biological significance lies in its role as a post-translational modification that modulates protein function, activity, localization, and interactions. S-nitrosation participates in the regulation of vascular tone, immune responses, and various signaling pathways, and it can influence enzyme activity and cytoskeletal dynamics. The balance between physiological signaling and nitrosative stress is influenced by cellular redox state, nitrosating agent availability, and the abundance of target thiols.

Detection and study of S-nitrosation are challenging due to the lability of S−NO bonds. Common approaches include indirect chemiluminescence assays for NO, the biotin-switch technique, fluorescence-based probes, and mass spectrometry to identify S-nitrosated residues. The term can be used interchangeably with S-nitrosylation in many contexts.