Solvent-accessible cysteine thiol group (Cys-SH)

Solvent-accessible cysteine thiol groups are highly reactive nucleophilic sites located on the surface of proteins, where they are available for interaction with the aqueous environment. These residues are vital for various biological functions, including enzymatic catalysis, metal ion coordination, and the regulation of redox signaling through reversible oxidation-reduction cycles (PubMed: 25590512, Chemical Reviews, 2015). In the context of pharmacology, these thiols are the primary targets for covalent inhibitors, which utilize electrophilic "warheads" to form stable, irreversible chemical bonds with the sulfur atom (Nature Reviews Drug Discovery, 2018). This mechanism allows for high potency and a prolonged duration of action that is independent of the drug's systemic half-life (Nature Reviews Drug Discovery, 2011). While targeting specific cysteines has been successful in developing therapies for various cancers—such as those targeting EGFR or BTK—the inherent reactivity of the thiol group presents significant challenges. Non-selective binding to off-target cysteines can lead to toxicity, immunogenicity through hapten formation, and other adverse effects (Chemical Reviews, 2015). Consequently, modern drug design focuses on achieving high selectivity by exploiting the unique microenvironment and pKa of the target cysteine residue (PubMed: 25590512).

Other names

Surface-exposed cysteinesReactive protein thiolsNucleophilic cysteine residuesCysteine proteome

Covalent modification of the thiol group via nucleophilic attack on an electrophilic drug moiety, typically through Michael addition.