Cysteine peptidases are a type of enzyme that break down proteins by cleaving peptide bonds. They contain a cysteine residue in their active site, which plays a crucial role in their catalytic activity. These enzymes are important in various biological processes, including protein degradation, cell signaling, and immune responses. These peptidases are found in many organisms, from bacteria to humans. They are involved in processes such as digestion and the regulation of cellular functions. Some cysteine peptidases are also studied for their potential therapeutic applications in treating diseases like cancer and inflammatory disorders.