Bonten E

References (2)

Title : The atomic model of the human protective protein\/cathepsin A suggests a structural basis for galactosialidosis - Rudenko_1998_Proc.Natl.Acad.Sci.U.S.A_95_621
Author(s) : Rudenko G , Bonten E , Hol WG , d'Azzo A
Ref : Proceedings of the National Academy of Sciences of the United States of America , 95 :621 , 1998
Abstract : Human protective protein/cathepsin A (PPCA), a serine carboxypeptidase, forms a multienzyme complex with beta-galactosidase and neuraminidase and is required for the intralysosomal activity and stability of these two glycosidases. Genetic lesions in PPCA lead to a deficiency of beta-galactosidase and neuraminidase that is manifest as the autosomal recessive lysosomal storage disorder galactosialidosis. Eleven amino acid substitutions identified in mutant PPCAs from clinically different galactosialidosis patients have now been modeled in the three-dimensional structure of the wild-type enzyme. Of these substitutions, 9 are located in positions likely to alter drastically the folding and stability of the variant protein. In contrast, the other 2 mutations that are associated with a more moderate clinical outcome and are characterized by residual mature protein appeared to have a milder effect on protein structure. Remarkably, none of the mutations occurred in the active site or at the protein surface, which would have disrupted the catalytic activity or protective function. Instead, analysis of the 11 mutations revealed a substantive correlation between the effect of the amino acid substitution on the integrity of protein structure and the general severity of the clinical phenotype. The high incidence of PPCA folding mutants in galactosialidosis reflects the fact that a single point mutation is unlikely to affect both the beta-galactosidase and the neuraminidase binding sites of PPCA at the same time to produce the double glycosidase deficiency. Mutations in PPCA that result in defective folding, however, disrupt every function of PPCA simultaneously.
ESTHER : Rudenko_1998_Proc.Natl.Acad.Sci.U.S.A_95_621
PubMedSearch : Rudenko_1998_Proc.Natl.Acad.Sci.U.S.A_95_621
PubMedID: 9435242
Gene_locus related to this paper: human-CTSA , mouse-Ppgb

Title : Three-dimensional structure of the human 'protective protein': structure of the precursor form suggests a complex activation mechanism - Rudenko_1995_Structure_3_1249
Author(s) : Rudenko G , Bonten E , d'Azzo A , Hol WG
Ref : Structure , 3 :1249 , 1995
Abstract : BACKGROUND The human 'protective protein' (HPP) forms a multi-enzyme complex with beta-galactosidase and neuraminidase in the lysosomes, protecting these two glycosidases from degradation. In humans, deficiency of HPP leads to the lysosomal storage disease galactosialidosis. Proteolytic cleavage of the precursor form of HPP involves removal of a 2 kDa excision peptide and results in a carboxypeptidase activity. The physiological relevance of this activity is, as yet, unknown. RESULTS: The crystal structure of the 108 kDa dimer of the precursor HPP has been elucidated by making extensive use of twofold density averaging. The monomer consists of a 'core' domain and a 'cap' domain. Comparison with the distantly related wheat serine carboxypeptidase dimer shows that the two subunits in the HPP dimer differ by 15 degrees in mutual orientation. Also, the helical subdomain forming part of the cap domains is very different. In addition, the HPP precursor cap domain contains a 'maturation' subdomain of 49 residues which fills the active-site cleft. Merely removing the 'excision' peptide located in the maturation subdomain does not render the catalytic triad solvent accessible.
CONCLUSIONS: The activation mechanism of HPP is unique among proteases with known structure. It differs from the serine proteases in that the active site is performed in the zymogen, but is blocked by a maturation subdomain. In contrast to the zinc metalloproteases and aspartic proteases, the chain segment physically rendering the catalytic triad solvent inaccessible in HPP is not cleaved off to form the active enzyme. The activation must be a multi-step process involving removal of the excision peptide and major conformational changes of the maturation subdomain, whereas the conformation of the enzymatic machinery is probably almost, or completely, unaffected.
ESTHER : Rudenko_1995_Structure_3_1249
PubMedSearch : Rudenko_1995_Structure_3_1249
PubMedID: 8591035
Gene_locus related to this paper: human-CTSA