Cysteïnproteases

Cysteïnproteases, also known as thiol proteases, are a class of enzymes that catalyze the breakdown of proteins by cleaving peptide bonds. Their defining characteristic is the presence of a cysteine residue in their active site, which plays a crucial role in the enzymatic mechanism. This cysteine nucleophile attacks the carbonyl carbon of a peptide bond, leading to the formation of a covalent intermediate. A histidine residue typically acts as a general base to deprotonate the cysteine, increasing its nucleophilicity, while an aspartate residue often stabilizes the positively charged histidine.

These enzymes are widely distributed in nature, found in organisms ranging from bacteria and viruses to plants and animals. They are involved in a diverse array of biological processes. In mammals, cysteïnproteases play significant roles in protein turnover, apoptosis (programmed cell death), immune responses, and the processing of secreted proteins. Examples include caspases, which are essential for apoptosis, and cathepsins, found in lysosomes, involved in intracellular digestion and antigen presentation.

Dysregulation of cysteïnprotease activity has been implicated in various diseases, including cancer, inflammatory disorders, and neurodegenerative conditions. Consequently, cysteïnproteases are attractive targets for therapeutic intervention. Inhibitors of specific cysteïnproteases are being developed and utilized for the treatment of conditions such as viral infections (e.g., HIV protease inhibitors) and parasitic diseases. The diverse functions and pathological relevance of cysteïnproteases make them a subject of ongoing research.