CST4
CST4 (cystatin S) is a secreted type 2 cystatin that inhibits cysteine proteases. It is an S-type cystatin, named for its high expression in saliva, tears and seminal plasma, and belongs to the cystatin family. Browse Assay Genie's current range of CST4 research reagents below, or read on for the biology behind the target.
CST4 is a cysteine protease inhibitor. In biochemical assays the protein strongly inhibits papain and ficin, partially inhibits stem bromelain and bovine cathepsin C, and does not inhibit porcine cathepsin B or clostripain. Papain is inhibited non-competitively. This selectivity profile distinguishes cystatin S from other members of the cystatin family and makes it a useful reference when studying how cysteine peptidases are regulated.
The CST4 gene sits in the cystatin locus on chromosome 20, which contains the majority of the type 2 cystatin genes and pseudogenes. HGNC places it in the type 2 cystatin gene group. The encoded protein is secreted, and the CST4 protein is classed as an S-type cystatin because of its high level of expression in saliva, tears and seminal plasma. The rat ortholog is Cst4.
The cystatin superfamily covers proteins with multiple cystatin-like sequences. Some members are active cysteine protease inhibitors, while others have lost, or perhaps never acquired, this activity. Three inhibitory families are recognised: the type 1 cystatins (stefins), the type 2 cystatins and the kininogens. Type 2 cystatins are found in a variety of human fluids and secretions. The specific role of cystatin S in these fluids is unclear, but antibacterial and antiviral activity has been reported, consistent with a protective function.
Cystatin S inhibits papain and ficin strongly and other cysteine proteases partially, making it a model for studying inhibitor selectivity.
High expression in saliva and tears makes CST4 relevant to research on the composition and function of these secretions.
As an S-type cystatin expressed in seminal plasma, CST4 is of interest when characterising proteins in this fluid.
Antibacterial and antiviral activity is reported for this protein, consistent with a protective function in body fluids.
CST4, or cystatin S, is a secreted cysteine protease inhibitor. It strongly inhibits papain and ficin, partially inhibits stem bromelain and bovine cathepsin C, and does not inhibit porcine cathepsin B or clostripain. Its specific role in body fluids is unclear, though antibacterial and antiviral activity is reported.
The protein is described as an S-type cystatin because of its high level of expression in saliva, tears and seminal plasma. It is a type 2 cystatin, a class of cysteine proteinase inhibitors found in a variety of human fluids and secretions.
CST4 belongs to the type 2 cystatins within the cystatin superfamily and lies in the cystatin locus on chromosome 20, alongside most other type 2 cystatin genes. A rat ortholog, Cst4, is listed; check the datasheet of any product for its validated reactivity.
Other cystatin family members, including type 1 and type 2 cystatins and related cysteine protease inhibitors.
Gene and protein annotations from HGNC, NCBI Gene and UniProt P01036; product specifications from Assay Genie datasheets.