Nisin is a polypeptide consisting of 34 amino acid residues with a molecular weight of approximately 3,500 Daltons. Its molecular structure is composed of five rings (A to E) and three methyl-lanthionine (MeLan) bridges. The rings are formed by amino acids with unusual modifications, including dehydroalanine, dehydrobutyrine, and lanthionine. The MeLan bridges are formed by the addition of a sulfur atom to two neighboring amino acids, creating a stable and rigid structure. These unique structural features of nisin contribute to its antimicrobial properties and stability in various conditions.