Cystatin

Cystatin is a type of protein that is known for its ability to inhibit cysteine proteases, which are enzymes that break down proteins and peptides. Cystatins are present in a wide variety of organisms and tissues, and they play a crucial role in numerous biological processes.

Function

Cystatins function primarily as inhibitors of cysteine proteases, which are enzymes that degrade proteins and peptides. These proteases are involved in a variety of biological processes, including protein recycling, digestion, and the immune response. By inhibiting these enzymes, cystatins help to regulate these processes and prevent excessive protein degradation.

Structure

Cystatins are typically small proteins, usually consisting of around 100 amino acids. They have a characteristic structure that includes two alpha helices and a five-stranded antiparallel beta sheet. This structure allows them to bind to and inhibit the active sites of cysteine proteases.

Types

There are several types of cystatins, which are classified based on their structure and function. These include:

• Type 1 cystatins: Also known as stefins, these are intracellular proteins that are found in all mammalian tissues.
• Type 2 cystatins: These are secreted proteins that are found in various body fluids, such as saliva and seminal fluid.
• Type 3 cystatins: Also known as kininogens, these are larger proteins that are involved in blood coagulation and inflammation.

Clinical significance

Cystatins have been implicated in a variety of diseases, including cancer, neurodegenerative diseases, and infectious diseases. For example, alterations in cystatin levels have been observed in patients with Alzheimer's disease, suggesting a potential role in the disease process. In addition, cystatins may have potential as therapeutic targets in the treatment of these diseases.

See also

• Cysteine protease
• Protein structure
• Alzheimer's disease

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