Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.23.5 (cathepsin D)
 4,130 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The N-acetylglucosaminyl-1-phosphotransferase (termed phosphotransferase) catalyzes the initial step in the formation of mannose 6-phosphate (M6P) residues required for the efficient transport of soluble lysosomal enzymes. The phosphotransferase is a multisubunit enzyme composed of three subunits (alpha2beta2gamma2) that are products of two genes. The gene encoding the gamma-subunit (GNPTAG) appears to be defective in patients with mucolipidosis type III (ML III). We have analyzed the GNPTAG gene in two siblings with ML III showing elevated activities of several lysosomal enzymes in cultured fibroblasts serum and diminished activities in cultured fibroblasts. Immunoprecipitation of metabolically labeled cathepsin D (CtsD) from fibroblasts revealed that the sorting/transport of this lysosomal protease was affected. Addition of ammonium chloride inhibiting pH-dependent processes, such as the CtsD-M6P receptor interaction, indicated that 15 to 20% of the newly synthesized CtsD is transported in ML III fibroblasts in an M6P-dependent manner. By direct sequencing a novel homozygous mutation, c.347_349delACA (p.Asn116del), was identified affecting a potential N-linked glycosylation site. Western blot analysis of extracts from control fibroblasts detect a 97 kDa glycosylated dimer whereas ML III cells contain a GNPTAG dimer of reduced molecular mass. These data suggest that the loss of the used glycosylation site in the gamma subunit may affect the intracellular localization of GNPTAG and the overall efficiency of M6P formation.
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PMID:A novel mutation in UDP-N-acetylglucosamine-1-phosphotransferase gamma subunit (GNPTAG) in two siblings with mucolipidosis type III alters a used glycosylation site. 1553 26

Mucolipidosis type III (ML III, pseudo-Hurler polydystrophy), an autosomal recessive inherited disorder of lysosomal enzyme targeting is due to a defective N-acetylglucosamine 1-phosphotransferase (phosphotransferase) activity and leads to the impaired formation of mannose 6-phosphate markers in soluble lysosomal enzymes followed by their increased excretion into the serum. Mutations in the phosphotransferase gamma subunit gene (GNPTAG) have been reported to be responsible for ML III. Here we report on a 14-year-old adolescent with a mild clinical phenotype of ML III. He presented with progressive joint stiffness and swelling. Urinary oligosaccharide and mucopolysaccharide excretion was normal. Lysosomal enzyme activities were significantly elevated in the serum and decreased in cultured fibroblasts. Impaired trafficking of the lysosomal protease cathepsin D (CtsD) was confirmed by metabolic labeling of the patient's fibroblasts. Neither mutations in the GNPTAG gene nor alterations in the GNPTAG mRNA level were detected whereas the steady state concentration of the 97 kDa GNPTAG dimer was reduced. Most importantly, the patient is homozygous for a pathogenic nucleotide substitution and a polymorphism in the phosphotransferase alpha/beta subunit gene (GNPTA). The data indicate that defects in genes other than GNPTAG can be linked to ML III contributing to the variability of the phenotype.
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PMID:Missense mutations in N-acetylglucosamine-1-phosphotransferase alpha/beta subunit gene in a patient with mucolipidosis III and a mild clinical phenotype. 1609 73

Mucolipidosis type II (ML II; I-cell disease) and mucolipidosis III (ML III; pseudo Hurler polydystrophy) are autosomal recessively inherited disorders caused by a defective N-acetylglucosamine 1-phosphotransferase (phosphotransferase). The formation of mannose 6-phosphate markers in soluble lysosomal enzymes is impeded leading to their increased excretion into the serum, to cellular deficiency of multiple hydrolases, and lysosomal storage of non-digested material. Phosphotransferase deficiency is caused by mutations in GNPTA and GNPTG encoding phosphotransferase subunits. Here we report on an adolescent with progressive joint contractions and other signs of mucolipidosis II who survived to the age of 14 years. Impaired trafficking of lysosomal enzymes cathepsin D and -hexosaminidase in metabolically labeled fibroblasts was documented. Mutations in the GNPTG gene and alterations in the GNPTG mRNA level were not detected. A different electrophoretic mobility of the 97 kDa GNPTG dimer suggested posttranslational modification abrogating the compartmentalization of GNPTG in the Golgi apparatus. A nucleotide substitution in the GNPTA gene (c.3707A>T) was identified altering the predicted C-terminal transmembrane anchor of the phosphotransferase subunit. The data demonstrate that defective GNPTA not only impairs lysosomal enzyme targeting but also the availability of intact GNPTG required for phosphotransferase activity and assembly of subunits.
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PMID:Missense mutation in the N-acetylglucosamine-1-phosphotransferase gene (GNPTA) in a patient with mucolipidosis II induces changes in the size and cellular distribution of GNPTG. 1683 5

Mucolipidosis type III gamma (MLIII, pseudo-Hurler polydystrophy) is a rare autosomal recessive disorder where the activity of the multimeric GlcNAc-1-phosphotransferase is reduced and formation of the mannose 6-phosphate (M6P) recognition marker on lysosomal enzymes is impaired. In this disease, the targeting of lysosomal enzymes is affected resulting in their hypersecretion, and an intracellular deficiency of multiple hydrolases. We report the biochemical and molecular diagnosis of MLIII in three siblings, aged 17, 15, and 14 years, who presented with joint pain and progressive joint stiffness. In addition to missorting of newly synthesized lysosomal protease cathepsin D, there were low levels of M6P-containing proteins in cell extracts and media of cultured fibroblasts of the Patients. Direct sequencing identified a novel homozygous mutation in intron 7, IVS7-10G>A, of the GNPTG gene, which encodes the gamma-subunit of the GlcNAc-1-phosphotransferase. This mutation created a cryptic 3'-splice site resulting in a frameshift and premature translational termination (p.V176GfsX18). The GNPTG mRNA levels were markedly reduced in Patients' fibroblasts indicating that the intronic mutation mediates mRNA decay, which was confirmed by absence of the gamma-subunit protein. These data contribute to an efficient diagnostic strategy to identify Patients with MLIII gamma and characterize their biochemical defect in fibroblasts.
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PMID:Loss of N-acetylglucosamine-1-phosphotransferase gamma subunit due to intronic mutation in GNPTG causes mucolipidosis type III gamma: Implications for molecular and cellular diagnostics. 2003 96

Newly synthesized soluble lysosomal hydrolases require mannose 6-phosphate (Man6P) residues on their oligosaccharides for their transport to lysosomes. The formation of Man6P residues is catalyzed by the GlcNAc-1-phosphotransferase, which is defective in the lysosomal storage disorders mucolipidosis type II (ML II) and ML III. Both hypersecretion and reduced intracellular level of lysosomal enzymes as well as direct sequencing of GlcNAc-1-phosphotransferase genes are important diagnostic markers for ML II and ML III. A high-affinity Man6P-specific single-chain antibody fragment was generated, allowing the rapid indirect demonstration of defective GlcNAc-1-phosphotransferase. In media and extracts of cultured fibroblasts of healthy controls but not of ML II and ML III patients, several Man6P-containing proteins could be detected by anti-Man6P Western blotting. Immunoprecipitation of Man6P-containing proteins from conditioned media or mouse brain extracts followed by arylsulfatase A and cathepsin D Western blotting confirmed the specificity of the antibody fragment for lysosomal proteins. Application of the antibody fragment in immunohistochemistry of human brain slices from nonaffected patients showed strong neuronal immunoreactivity, which was not observed in cortical sections of an ML II patient. Finally, in brain extracts of a novel GlcNAc-1-phosphotransferase knock-in mouse no Man6P-containing proteins were detectable. Thus, the single-chain antibody fragment against Man6P was demonstrated to allow the specific, rapid, and convenient detection of Man6P-containing proteins and facilitates the diagnosis of ML II and ML III.
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PMID:A novel single-chain antibody fragment for detection of mannose 6-phosphate-containing proteins: application in mucolipidosis type II patients and mice. 2047 86