CSTA Human, Active

Cystatin-A, also known as stefin A, is a member of the cystatin superfamily, which encompasses proteins containing multiple cystatin-like sequences. These proteins are primarily known for their role as cysteine protease inhibitors. Cystatin-A is particularly significant due to its function in inhibiting cysteine proteases such as papain and the cathepsins B, H, and L .

Recombinant human Cystatin-A is typically produced using an E. coli expression system. The protein is expressed with a sequence (Met1-Phe98) of human Cystatin-A, often fused with a 6×His tag at the C-terminus to facilitate purification . The molecular mass of Cystatin-A is approximately 12 kDa .

Cystatin-A functions as a cysteine protease inhibitor, forming tight complexes with target proteases. This inhibitory activity is crucial for regulating the proteolytic activity within cells. The protein’s ability to inhibit papain cleavage of a fluorogenic peptide substrate is often used to measure its bioactivity, with an IC50 value of less than 0.7 nM .

Cystatin-A plays a vital role in epidermal development and maintenance. It is one of the precursor proteins of the cornified cell envelope in keratinocytes, contributing to the formation of the skin barrier . Additionally, stefins, including Cystatin-A, have been proposed as prognostic and diagnostic tools for cancer due to their regulatory functions in protease activity .

Recombinant human Cystatin-A is used extensively in research to study its inhibitory effects on cysteine proteases. It is also utilized in various assays to understand its role in cellular processes and its potential implications in diseases such as cancer .

For long-term storage, the lyophilized protein should be kept at -20°C to -80°C. After reconstitution, the protein solution is stable at -20°C for up to three months and at 2-8°C for up to one week. It is recommended to add a carrier protein or stabilizer to the reconstituted solution to minimize freeze-thaw cycles .