Protein cysteine residues (Cys) (Cys)

Protein cysteines are amino acid residues characterized by a highly nucleophilic thiol (-SH) side chain, which is essential for various biological processes including enzymatic catalysis, metal ion coordination, and the formation of stabilizing disulfide bonds (Singh et al., 2011, Nature Reviews Drug Discovery). They serve as critical sensors in redox signaling, where the oxidation state of the thiol group can modulate protein function in response to cellular oxidative stress (Go & Jones, 2013, Free Radical Biology and Medicine). In drug discovery, specific cysteine residues are targeted by covalent inhibitors—such as Ibrutinib targeting Cys481 in Bruton's tyrosine kinase—to achieve high potency and prolonged pharmacological effects (Backus et al., 2016, Nature). However, because cysteines are ubiquitous across the proteome, the term "Protein cysteines" refers to a broad chemical class rather than a single therapeutic entity, making global targeting a challenge due to potential off-target reactivity and toxicity (Resnick et al., 2024, Journal of Medicinal Chemistry). Consequently, while individual cysteines within specific proteins are high-value targets, the collective group of protein cysteines is not considered a single drug target.

Other names

Cysteine residuesProtein thiolsCysReactive cysteinesCysteinome

Covalent modification of the cysteine thiol group via electrophilic warheads, typically through Michael addition or nucleophilic substitution, to irreversibly or reversibly inhibit protein function.