How do disulfide bonds help proteins keep their shape?

Disulfide bonds, also known as disulfide bridges, are essential for maintaining the specific three-dimensional shapes, or tertiary structures, of many proteins. These bonds form when the sulfur atoms of two cysteine amino acid molecules bond together to create cystine.123

Because these cysteine residues can be located in different parts of a peptide chain, the resulting disulfide bond acts as a structural anchor that pulls those sections together, often forming a closed loop. This covalent linkage provides significant stability to the protein's conformation, which is critical for its biological activity.21

The importance of these bonds is particularly evident in structural proteins like keratin, where they contribute to great stability. If these disulfide bonds are reduced—meaning the sulfur-sulfur bond is broken and converted back into two sulfhydryl (—SH) groups—the protein's tertiary structure can undergo a drastic change, causing loops to open and peptide chains to separate.32