1ivy
From Proteopedia
|
PHYSIOLOGICAL DIMER HPP PRECURSOR
Overview
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.
About this Structure
1IVY is a Single protein structure of sequence from Homo sapiens with NAG as ligand. Active as Carboxypeptidase C, with EC number 3.4.16.5 Structure known Active Site: CAT. Full crystallographic information is available from OCA.
Reference
Three-dimensional structure of the human 'protective protein': structure of the precursor form suggests a complex activation mechanism., Rudenko G, Bonten E, d'Azzo A, Hol WG, Structure. 1995 Nov 15;3(11):1249-59. PMID:8591035
Page seeded by OCA on Mon Nov 5 16:40:14 2007
