Cystatins are endogenous inhibitors of papain‐like cysteine proteases. Since the discovery that a polypeptide from chicken egg‐whites (chicken cystatin) could inhibit the plant cysteine protease, papain, more than 40 mammalian cystatins have been isolated.

Keywords: cystatins; stefins; kininogens; cathepsins; cysteine protease inhibitors

Figure 1.

Amino acid alignment of cystatins. The numbering refers to the first residue of the mature protein. Dashes indicate gaps introduced to optimize alignments. Boxes indicate residues that are involved in inhibition of papain‐like cysteine proteases. The dashed box indicates a domain involved in the inhibition of legumain. Shaded areas indicate residues in cystatins capable of inhibiting legumain. Solid brackets indicate disulfide bridges in members of family 2 and 3 cystatins, dashed bracket indicates a disulfide bridge unique to cystatin F, and the double bracket indicates a disulfide bridge present in kininogen domains D2 and D3. The N‐glycosylation sites in cystatins E/M and F are indicated by bold, underlined N's (asparagine). The bold, underlined S's (serine) in cystatin S indicate phosphorylation sites and that in cystatin M indicate a potential phosphorylation site.



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Further Reading

Abrahamson M (1994) Cystatins. Methods in Enzymology 244: 685–700.

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Lah TT and Kos J (1998) Cysteine proteinases in cancer progression and their clinical relevance for prognosis. Biological Chemistry 379: 125–130.

Sloane BF, Rozhin J, Robinson D and Honn KV (1990) Role for cathepsin B and cystatins in tumor growth and progression. Biological Chemistry Hoppe‐Seyler 371(supplement): 193–198.

Turk V and Bode W (1991) The cystatins: protein inhibitors of cysteine proteinases. Federation of European Biochemical Society Letters 285: 213–219.

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Shridhar, Ravi, Keppler, Daniel, and Sloane, Bonnie F(Sep 2006) Cystatins. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0005904]