Kathepszinok

Kathepszinok, in English commonly called cathepsins, are a family of proteolytic enzymes largely confined to lysosomes where they participate in the degradation and turnover of proteins. They play key roles in intracellular protein recycling, endocytosis, and autophagy, helping to maintain cellular homeostasis and respond to nutrient stress or damage.

The cathepsin family is diverse and includes several classes. Most members are cysteine proteases of the papain superfamily, such as cathepsins B, C, F, H, L, S, K, O, V, and W. Cathepsins D and E are aspartic proteases, while cathepsins G and A are serine proteases found in specific cell types, particularly immune cells. The enzymes differ in substrate specificity, pH optima, and subcellular localization, reflecting their varied physiological roles.

Biogenesis and regulation: Cathepsins are typically synthesized as inactive zymogens (procathepsins) and are trafficked to the endolysosomal system. Within the acidic lysosomal environment, they undergo proteolytic processing to become active. Activity is tightly regulated by endogenous inhibitors such as cystatins and, in some contexts, serpins, which help prevent unintended proteolysis in the cytosol and extracellular space.

Physiological and pathological roles: In healthy tissue, cathepsins contribute to general protein turnover and antigen processing for MHC class II presentation. Secreted cathepsins can remodel the extracellular matrix, participate in wound healing, and influence tissue development. Dysregulation or overexpression of cathepsins is linked to diseases including cancer (promotion of invasion and metastasis), osteoporosis (cathepsin K-mediated bone resorption), and neurodegenerative conditions, making them targets for therapeutic inhibition.

Genetics and research: Human cathepsins are encoded by genes such as CTSB, CTSL, CTSK, CTSD, CTSG, and CTSE, among others. Research continues to elucidate their precise roles in health and disease and to develop selective inhibitors for clinical use.