Cathepsins

Cathepsins are a group of protease enzymes found in all animals as well as other organisms. They are crucial for various cellular processes, including protein degradation, antigen presentation, and apoptosis. Cathepsins are primarily located in the lysosomes, where they function optimally at the acidic pH found in these organelles.

Types of Cathepsins

Cathepsins are classified based on their catalytic mechanism into three main types:

• Cysteine cathepsins (e.g., Cathepsin B, Cathepsin L, Cathepsin S)
• Aspartic cathepsins (e.g., Cathepsin D, Cathepsin E)
• Serine cathepsins (e.g., Cathepsin G)

Functions

Cathepsins play a variety of roles in the body:

• Protein Degradation: They break down proteins into amino acids, which can then be reused by the cell.
• Antigen Presentation: Cathepsins are involved in the processing of antigens for presentation on major histocompatibility complex (MHC) molecules.
• Apoptosis: They participate in the controlled process of cell death, which is essential for maintaining cellular homeostasis.

Clinical Significance

Dysregulation of cathepsin activity is associated with several diseases, including:

• Cancer: Overexpression of certain cathepsins can contribute to tumor progression and metastasis.
• Osteoporosis: Cathepsin K is involved in bone resorption, and its overactivity can lead to excessive bone loss.
• Neurodegenerative diseases: Abnormal cathepsin activity is linked to conditions such as Alzheimer's disease.

Related Pages

• Protease
• Lysosome
• Apoptosis
• Antigen presentation
• Major histocompatibility complex
• Cancer
• Osteoporosis
• Neurodegenerative diseases