The cystatin superfamily encompasses proteins that contain multiple cystatin-like sequences. Some of the members are active cysteine protease inhibitors, while others have lost or perhaps never acquired this inhibitory activity.
There are three inhibitory families in the superfamily, including the type 1 cystatins (stefins), type 2 cystatins and the kininogens. The type 2 cystatin proteins are a class of cysteine proteinase inhibitors found in a variety of human fluids and secretions.
The cystatin locus on chromosome 20 contains the majority of the type 2 cystatin genes and pseudogenes. This gene is located in the cystatin locus and encodes an epididymal-specific protein whose specific function has not been determined. Alternative splicing yields two variants encoding distinct isoforms.[5]
Saitoh E, Isemura S, Sanada K, et al. (1989). "Cystatin superfamily. Evidence that family II cystatin genes are evolutionarily related to family III cystatin genes". Biol. Chem. Hoppe-Seyler. 369 Suppl: 191–7. PMID3202964.
Dickinson DP, Thiesse M, Dempsey LD, Millar SJ (1993). "Genomic cloning, physical mapping, and expression of human type 2 cystatin genes". Crit. Rev. Oral Biol. Med. 4 (3–4): 573–80. doi:10.1177/10454411930040034401. PMID7690606.
Dickinson DP, Zhao Y, Thiesse M, Siciliano MJ (1995). "Direct mapping of seven genes encoding human type 2 cystatins to a single site located at 20p11.2". Genomics. 24 (1): 172–5. doi:10.1006/geno.1994.1595. PMID7896273.
Thiesse M, Millar SJ, Dickinson DP (1994). "The human type 2 cystatin gene family consists of eight to nine members, with at least seven genes clustered at a single locus on human chromosome 20". DNA Cell Biol. 13 (2): 97–116. doi:10.1089/dna.1994.13.97. PMID8179826.
