Title: Cystatins
Literature References: Protein superfamily of endogenous cysteine proteinase inhibitors. All inhibit papain-type peptidases, including serveral cathepsins. Widely distributed in animals, plants, and protozoa; at least 12 cystatins have been identified in humans. Type 1 (cystatins A and B), also known as stefins, are intracellular, single-chain peptides of ~100 residues with no disulfide bonds or carbohydrate. Type 2, comprising the largest group, are extracellular, secreted proteins, typically 120-125 residues with 2 disulfide bonds; broadly distributed and found in most body fluids. Type 3, known as kininogens, q.v., are intravascular, multi-functional, glycosylated proteins of mol wt 60-120 kDa that also serve as kinin precursors. Discovery of a papain inhibitor in chicken egg white: K. Fossum, J. R. Whitaker, Arch. Biochem. Biophys. 125, 367 (1968). Sequence homologies and evolutionary relationship: W. Müller-Esterl et al., FEBS Lett. 191, 221 (1985). Review of physiological role in malignant progression and prognosis: J. Kos, T. T. Lah, Oncol. Rep. 5, 1349-1361 (1998). Reviews: A. J. Barrett, Biomed. Biochim. Acta 45, 1363-1374 (1986); M. Abrahamson et al., Biochem. Soc. Symp. 70, 179-199 (2003).
Derivative Type: Cystatin A
CAS Registry Number: 107544-29-6
Additional Names: Stefin A; CPI-A; acidic cysteine proteinase inhibitor
Literature References: Found primarily in epithelial cells and polymorphonuclear leukocytes; also occurs in amniotic fluid and tears. Purification from human epidermis: M. Järvinen, J. Invest. Dermatol. 72, 114 (1978); from human granulocytes: J. Brzin et al., Z. Phys. Chem. 364, 1475 (1983).
Properties: Mature human form is a single chain, non-glycosylated peptide containing 98 amino acid residues; mol wt 11.0 kDa. Isoelectric point: 4.5-4.7.
Derivative Type: Cystatin B
CAS Registry Number: 99194-04-4
Additional Names: Stefin B; CPI-B; NCPI; neutral cysteine proteinase inhibitor
Literature References: Broadly distributed in human cells and tissues; general cytosolic inhibitor to protect against leakage of lysosomal enzymes. Mutations in the cystatin B gene have been associated with progressive myoclonus epilepsy. Isoln from human spleen: M. Järvinen, A. Rinne, Biochim. Biophys. Acta 708, 210 (1982); from human liver: G. D. J. Green et al., Biochem. J. 218, 939 (1984). Review of role in Unverricht-Lundborg disease: A.-E. Lehesjoki, EMBO J. 22, 3473-3478 (2003).
Properties: Mature human form is a single chain, non-glycosylated peptide containing 98 amino acid residues; mol wt 11.2 kDa. Isoelectric point: 5.6-6.3.
Derivative Type: Cystatin C
CAS Registry Number: 91448-99-6
Additional Names: Post-g-globulin; g-CSF; g-trace
Literature References: Found ubiquitously in vertebrates; major extracellular cysteine peptidase inhibitor in mammals. Isoln from human CSF: J. Clausen, Proc. Soc. Exp. Biol. Med. 107, 170 (1961); from urine of patients with renal dysfunction: E. A. Butler, F. V. Flynn, J. Clin. Pathol. 14, 172 (1961). Identification as a cystatin: A. J. Barrett et al., Biochem. Biophys. Res. Commun. 120, 631 (1984). Review of biochemistry and clinical role: M. Mussap, M. Plebani, Crit. Rev. Clin. Lab. Sci. 41, 467-550 (2004); of efficacy as biomarker for glomerular filtration rate: G. Filler et al., Clin. Biochem. 38, 1-8 (2005). Clinical evaluation to predict risk of cardiovascular events in elderly patients: M. G. Shlipak et al., N. Engl. J. Med. 352, 2049 (2005).
Properties: Mature human form is a single chain, non-glycosylated peptide containing 120 amino acid residues; mol wt 13.3 kDa. Isoelectric point: 9.3. Electrophoretic mobility: g3 (agarose gel electrophoresis at pH 8.6). E1cm1% 9.1 (280 nm). Conc in plasma of healthy adults: 0.8 to 1.2 mg/l.
Therap-Cat: Cystatin C as diagnostic aid (renal function).

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