Cysteine proteinases (pronounced /ˈsɪstiːn prəʊtiːneɪsɪz/) are enzymes that break down proteins and peptides in biological organisms. The word "cysteine" is spelled with a "c" and pronounced as /sɪstiːn/, not /kɪstiːn/, despite the similarity in spelling with words like "cyber" and "cycle". The word "proteinases" is spelled with an "i" after the prefix "prote-", reflecting the pronunciation /prəʊtiːneɪsɪz/ with emphasis on the second syllable. Together, these enzymes play important roles in many physiological processes and diseases.
Cysteine proteinases, also known as cysteine proteases, are a subclass of proteases that belong to the larger group of enzymes known as peptidases. These enzymes are responsible for cleaving peptide bonds in proteins and peptides by hydrolyzing them.
Cysteine proteinases are characterized by the presence of the amino acid cysteine in their active sites. The thiol group of the cysteine residue is involved in catalyzing the cleavage of the peptide bond. This distinguishes them from other classes of proteases, such as serine proteases and metalloproteinases, which use different mechanisms for catalysis.
These proteinases play crucial roles in numerous physiological processes, including digestion, immune response, apoptosis, and tissue remodeling. They are found in a wide range of organisms, including bacteria, fungi, plants, and animals. Examples of cysteine proteinases include papain, cathepsins, calpains, and caspases.
Due to their physiological importance, cysteine proteinases have emerged as potential targets for therapeutic interventions. Inhibitors of these enzymes have been developed for the treatment of diseases associated with their dysregulation, such as cancer, autoimmune disorders, and infectious diseases.
In summary, cysteine proteinases are a subclass of proteases that utilize cysteine in their active sites to catalyze the hydrolysis of peptide bonds. They play critical roles in various biological processes and are important targets for drug development.
The word "cysteine proteinases" is derived from two main components: "cysteine" and "proteinases".
1. Cysteine: The term "cysteine" refers to an amino acid that is frequently found in proteins. It is named after cystine, which was the original name given to a crystal isolated from a bladder stone (cystinuria) by William Hyde Wollaston in 1810. The name "cystine" comes from the Greek word "kystis", meaning bladder.
2. Proteinases: The term "proteinases" is derived from the word "protease", which refers to enzymes that break down proteins into smaller peptides or amino acids.