What is the three-letter code for the amino acid cysteine and what role does it play in protein structure and function?

The three-letter code for the amino acid cysteine is Cys. Cysteine plays a crucial role in protein structure and function by forming disulfide bonds with other cysteine residues, which help stabilize the protein's three-dimensional structure. These bonds are important for maintaining the overall shape and stability of proteins, as well as influencing their function.