disulfidebonded

Disulfidebonded describes molecules in which two thiol groups, typically from cysteine residues, have formed a covalent disulfide bond (S-S). This linkage can occur within a single polypeptide (intramolecular) or between two polypeptides (intermolecular) and is a key factor in stabilizing three-dimensional structure and quaternary assembly. The term is commonly applied to proteins and peptides that acquire or maintain their functional conformations through disulfide bonds.

Formation and regulation of disulfide bonds occur primarily in oxidizing cellular environments. In eukaryotes, disulfide bonds are usually formed in the endoplasmic reticulum with the help of enzymes such as protein disulfide isomerase (PDI), which catalyzes formation, breakage, and rearrangement of S-S linkages. In bacteria and archaea, similar processes take place in the periplasm or other oxidizing compartments. The cellular cytosol is generally reducing, so most cytosolic proteins are disulfidebonded only transiently or not at all unless specialized redox systems are present.

Disulfide bonds contribute to protein folding, stability, and resistance to proteolysis. They also play roles in redox regulation and the assembly of multimeric complexes. Abnormal disulfide bonding can affect function and is implicated in various diseases. Disulfidebonded states can be analyzed by methods such as alkylation of free thiols, mass spectrometry, and structural techniques, which help map which cysteines are linked.

Examples include many extracellular and secreted proteins, antibodies, and enzymes where disulfide bonds lock active or binding conformations. The balance between reduced and oxidized cysteines governs the dynamic behavior of disulfidebonded systems in cells.