| Structural highlights
Disease
[PPGB_HUMAN] Defects in CTSA are the cause of galactosialidosis (GSL) [MIM:256540]. A lysosomal storage disease associated with a combined deficiency of beta-galactosidase and neuraminidase, secondary to a defect in cathepsin A. All patients have clinical manifestations typical of a lysosomal disorder, such as coarse facies, cherry red spots, vertebral changes, foam cells in the bone marrow, and vacuolated lymphocytes. Three phenotypic subtypes are recognized. The early infantile form is associated with fetal hydrops, edema, ascites, visceromegaly, skeletal dysplasia, and early death. The late infantile type is characterized by hepatosplenomegaly, growth retardation, cardiac involvement, and a normal or mildly affected mental state. The juvenile/adult form is characterized by myoclonus, ataxia, angiokeratoma, mental retardation, neurologic deterioration, absence of visceromegaly, and long survival.[1] [2] [3] [4]
Function
[PPGB_HUMAN] Protective protein appears to be essential for both the activity of beta-galactosidase and neuraminidase, it associates with these enzymes and exerts a protective function necessary for their stability and activity. This protein is also a carboxypeptidase and can deamidate tachykinins.[5]
Publication Abstract from PubMed
Galactosialidosis is a human lysosomal storage disease caused by deficiency in the multifunctional lysosomal protease cathepsin A (also known as protective protein/cathepsin A, PPCA, catA, HPP, and CTSA; EC 3.4.16.5). Previous structural work on the inactive precursor human cathepsin A (zymogen) led to a two-stage model for activation, where proteolysis of a 1.6-kDa excision peptide is followed by a conformational change in a blocking peptide occluding the active site. Here we present evidence for an alternate model of activation of human cathepsin A, needing only cleavage of a 3.3-kDa excision peptide to yield full enzymatic activity, with no conformational change required. We present x-ray crystallographic, mass spectrometric, amino acid sequencing, enzymatic, and cellular data to support the cleavage-only activation model. The results clarify a longstanding question about the mechanism of cathepsin A activation and point to new avenues for the design of mechanism-based inhibitors of the enzyme.
Proteolytic activation of human cathepsin A.,Kolli N, Garman SC J Biol Chem. 2014 Apr 25;289(17):11592-600. doi: 10.1074/jbc.M113.524280. Epub, 2014 Mar 5. PMID:24599961[6]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Zhou XY, Galjart NJ, Willemsen R, Gillemans N, Galjaard H, d'Azzo A. A mutation in a mild form of galactosialidosis impairs dimerization of the protective protein and renders it unstable. EMBO J. 1991 Dec;10(13):4041-8. PMID:1756715
- ↑ Shimmoto M, Fukuhara Y, Itoh K, Oshima A, Sakuraba H, Suzuki Y. Protective protein gene mutations in galactosialidosis. J Clin Invest. 1993 Jun;91(6):2393-8. PMID:8514852 doi:http://dx.doi.org/10.1172/JCI116472
- ↑ Zhou XY, van der Spoel A, Rottier R, Hale G, Willemsen R, Berry GT, Strisciuglio P, Morrone A, Zammarchi E, Andria G, d'Azzo A. Molecular and biochemical analysis of protective protein/cathepsin A mutations: correlation with clinical severity in galactosialidosis. Hum Mol Genet. 1996 Dec;5(12):1977-87. PMID:8968752
- ↑ Takiguchi K, Itoh K, Shimmoto M, Ozand PT, Doi H, Sakuraba H. Structural and functional study of K453E mutant protective protein/cathepsin A causing the late infantile form of galactosialidosis. J Hum Genet. 2000;45(4):200-6. PMID:10944848 doi:10.1007/s100380070027
- ↑ Galjart NJ, Morreau H, Willemsen R, Gillemans N, Bonten EJ, d'Azzo A. Human lysosomal protective protein has cathepsin A-like activity distinct from its protective function. J Biol Chem. 1991 Aug 5;266(22):14754-62. PMID:1907282
- ↑ Kolli N, Garman SC. Proteolytic activation of human cathepsin A. J Biol Chem. 2014 Apr 25;289(17):11592-600. doi: 10.1074/jbc.M113.524280. Epub, 2014 Mar 5. PMID:24599961 doi:http://dx.doi.org/10.1074/jbc.M113.524280
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