CysteinThiolate

CysteinThiolate, commonly referred to as the cysteine thiolate, is the deprotonated form of the thiol side chain of the amino acid cysteine. Upon loss of a proton from the thiol group (–SH), cysteine forms the thiolate anion (–S−). In physiological pH, a fraction exists as the thiolate; the pKa of the cysteine thiol is about 8.3 in many contexts, with environmental factors in proteins shifting it.

The thiolate sulfur is a soft Lewis base and a strong nucleophile, readily engaging in alkylation and Michael-type additions, and it coordinates with metal ions. In proteins and enzymes, cysteinyl thiolates act as ligands for metal centers such as Zn2+ and Fe-S clusters, and participate in catalytic redox chemistry. They participate in redox signaling via thiol-disulfide exchange, and can form disulfide bonds with other cysteine residues (giving cystine) under oxidizing conditions.

Biological roles of cysteine thiolates include contributions to enzyme catalysis, metal binding in metalloproteins, and maintaining redox balance as part of glutathione-related chemistry. Local environment, pH, hydrogen bonding, and nearby charges significantly influence the acidity and reactivity of the thiol group, potentially stabilizing the thiolate form in active sites.

In summary, cysteinThiolate denotes the reactive thiolate form of cysteine’s side chain, central to metal coordination, redox biology, and covalent modification of proteins.