Sguanylation

Sguanylation is a post-translational modification in which a guanine-derived moiety covalently attaches to a cysteine thiol within a protein, forming an S-guanylated cysteine. It is considered a redox-related modification that can arise under nitrosative and oxidative stress when reactive nitrogen species and nucleotide-derived electrophiles are present. Sguanylation is distinct from S-glutathionylation, which involves glutathione as the modifying group; in Sguanylation, the modifying moiety is guanine-containing.

The modification has been observed in both prokaryotic and eukaryotic systems and can influence protein function by altering the redox state, steric properties, or reactivity of cysteine residues. In some contexts, S-guanylation may act as a reversible switch that protects protein thiols from irreversible overoxidation, whereas in others it can inactivate enzymes or modify activity.

Mechanistically, S-guanylation is thought to occur through reaction of thiolate cysteines with guanine-derived electrophiles generated during cellular stress. The exact pathways and enzymes responsible for addition and removal are not fully resolved; evidence supports both non-enzymatic and enzymatic routes depending on context.

Detection and study typically rely on mass spectrometry-based proteomics and biochemical assays that identify guanine-containing adducts on cysteine residues. The biological significance of Sguanylation is an active area of redox biology, with ongoing research into its reversibility, regulation, and role in disease.

See also: S-glutathionylation, nitrosative stress, redox signaling.