Protein cysteine residues (Cys)

Protein cysteine residues are unique amino acids characterized by a nucleophilic thiol (-SH) side chain, which serves as a versatile functional group in cellular biology. They are fundamental to protein architecture through the formation of disulfide bonds and are critical for the catalytic activity of various enzymes, including proteases and phosphatases (PMID: 29107040). In drug discovery, these residues are strategically targeted by covalent inhibitors that employ electrophilic warheads to form permanent bonds, thereby enhancing the drug's potency and duration of action (Nature Reviews Drug Discovery, 2011, 10, 307–317). This mechanism is utilized by several FDA-approved drugs to treat conditions such as non-small cell lung cancer and B-cell malignancies by targeting specific cysteines in kinases like EGFR and BTK (PMID: 30245440). Despite their therapeutic utility, the broad distribution of reactive cysteines across the proteome presents significant challenges, as non-specific binding can lead to off-target toxicity or the formation of immunogenic drug-protein adducts (PMID: 21455239).

Other names

Protein thiolsSulfhydryl groupsCysteine side chainsReactive cysteinesProtein-bound cysteine

Covalent modification of the nucleophilic thiol group via electrophilic attack (e.g., Michael addition), leading to irreversible or slowly reversible inhibition of the target protein's function.