Cysteine residue

Cysteine residues refer to the amino acid cysteine (Cys) when incorporated into protein sequences. Cysteine has a unique thiol (-SH) side chain that is highly reactive and can participate in a range of chemical modifications. Cysteine residues frequently form disulfide bonds (covalent S–S links) either within or between protein chains, which provide structural stability and rigidity to proteins, especially those secreted outside the cell or localized to oxidizing environments[1][2][3][4]. They also serve as key sites for catalytic redox chemistry (e.g., in thiol-based enzymes), protein regulation via reversible oxidation or other post-translational modifications, and metal ion coordination (such as in zinc-finger domains)[1][3][4][5][6]. Their modification state can serve as a signal for cellular status, such as oxidative stress or redox signaling. Cysteine residues are not a single targetable entity, but their importance in protein chemistry makes them critical for understanding protein function and pathology in numerous contexts.

Other names

Cys residueprotein cysteinecysteinyl residue