Kathepsins

Kathepsins are a group of cysteine proteases found in a wide variety of organisms, from bacteria to humans. In mammals, they are primarily lysosomal enzymes, meaning they function within the acidic environment of lysosomes, cellular organelles responsible for breaking down waste materials and cellular debris. They play crucial roles in a multitude of biological processes, including protein degradation, antigen presentation, bone resorption, and muscle degradation. The precise function of a specific cathepsin is often determined by its substrate specificity and its cellular localization.

There are numerous types of cathepsins, classified into different families based on their structural similarities and sequence homology. The main families in mammals are cathepsins B, C, D, F, H, K, L, O, S, V, X, and Z. Each of these cathepsins has distinct roles. For example, cathepsin K is predominantly involved in bone remodeling, while cathepsin S is important for the processing of antigens in immune cells. Dysregulation of cathepsin activity has been implicated in a range of diseases, including cancer, osteoporosis, rheumatoid arthritis, and neurodegenerative disorders. Consequently, cathepsins are considered important therapeutic targets for various pathological conditions. Research continues to explore their diverse functions and potential as drug targets.