Mucolipidosis type II and type III

Co-Project Leader: Sandra Pohl

  • Research
  • Research
    GlcNAc-1-phosphotransferase and lysosomal dysfunction
    Lupe zum Vergrößern des Bildes
    GlcNAc-1-phosphotransferase and lysosomal dysfunction

    M6P-dependent transport of lysosomal enzymes in health and disease

    Soluble lysosomal enzymes are synthesized in the ER and transported to the Golgi apparatus where they are being equipped with M6P residues by the GlcNAc-1-phosphotransferase. The M6P-modified lysosomal enzymes are recognized by M6P receptors in the trans-Golgi network. The receptor-enzyme complexes are transported via endosomes where the acidic pH causes the dissociation of the complexes and the lysosomal enzymes are delivered to lysosomes. The GlcNAc-1-phosphotransferase activity is deficient or reduced in two distinct autosomal recessive human diseases of lysosomal enzyme trafficking, mucolipidosis (ML) II and MLIII. As a consequence, lysosomal enzyme are secreted into the extracellular space and non-degradable macromolecules accumulate in the lysosomes and leads to lysosomal dysfunction.

     Proteolytic activation of GlcNAc-1-phosphotransferase by S1P
    Lupe zum Vergrößern des Bildes
    Proteolytic activation of GlcNAc-1-phosphotransferase by S1P

    The GlcNAc-1-phosphotransferase form a hexameric complex of three subunits (α2β2γ2). The α- and β-subunits (encoded by GNPTAB) comprise the catalytic site, while the function of the γ-subunit (encoded by GNPTG) remains unknown. The human α- and β-subunits are synthesized as a common precursor protein. The α/β-subunit precursor is synthesized as a 190 kDa type III membrane protein. After synthesis and assembly of the GlcNAc-1-phosphotransferase subunits in the ER, the complex is transported to the cis-Golgi compartment. Upon arrival in the cis-Golgi apparatus, the α/β-subunit precursor is proteolytically cleaved by the site-1 protease between amino acids K928 and D929 into the mature α- and β-subunits. The S1P-mediated cleavage α/β-subunit precursor protein in the Golgi apparatus is prerequisite for the catalytic activity of the GlcNAc-1-phosphotransferase.

    Projects:

    • Proteolytic activation and subunit assembly of the GlcNAc-1-phosphotransferase
    • Role of the subunits for GlcNAc-1-phosphotransferase activity
    • Regulation of lysosomal enzyme trafficking by ER- and Golgi-resident proteins
    • Function and dysfunction of lysosomes
    • Analysis of patient cells and mouse models for the lysosomal storage diseases

  • Project-relevant Publications

    • Subunit interactions of the disease-related hexameric GlcNAc-1-phosphotransferase complex. De Pace R, Velho RV, Encarnação M, Marschner K, Braulke T, Pohl S (2015) Hum Mol Genet 24:6826-35 Abstract

    • Site-1 protease-activated formation of lysosomal targeting motifs is independent of the lipogenic transcription control. Klünder S, Heeren J, Markmann S, Santer R, Braulke T, Pohl S (2015) J Lipid Res 56:1625-1632 Abstract

    • Analyses of disease-related GNPTAB mutations define a novel GlcNAc-1-phosphotransferase interaction domain and an alternative site-1 protease cleavage site. Velho RV, De Pace R, Klünder S, Sperb-Ludwig F, Lourenço CM, Schwartz IV, Braulke T, Pohl S (2015) Hum Mol Genet 24:3497-3505 Abstract
    • A key enzyme in the biogenesis of lysosomes is a protease that regulates cholesterol metabolism. Marschner K, Kollmann K, Schweizer M, Braulke T, Pohl S (2011) Science 333:87-90 Abstract
    • Posttranslational modifications of the γ-subunit affect intracellular trafficking and complex assembly of the GlcNAc-1-phosphotransferase. Encarnação M, Kollmann K, Trusch M. Braulke T, Pohl S (2011) J Biol Chem 286:5311-18 Abstract
    • Proteolytic processing of the γ-subunit is associated with the failure to form GlcNAc-1-phosphotransferase complexes and mannose 6-phosphate residues on lysosomal enzymes in human macrophages. Pohl S, Tiede S, Marschner K, Encarnação M, Castrichini M, Kollmann K, Muschol N, Ullrich K, Müller-Loennies S, Braulke T (2010) J Biol Chem 285:23936-44 Abstract
    • Mucolipidosis II is caused by mutations in GNPTA encoding the alpha/beta GlcNAc-1-phosphotransferase. Tiede S, Storch S, Lübke T, Henrissat B, Bargal R, Raas-Rothschild A, Braulke T (2005) Nat Med 11:1109-12 Abstract

  • Current funding

    Logo DFG

    04/2018 - 03/2021
    Sandra Pohl
    German Research Foundation (DFG)
    Grant PO 1539/1-1
    „Role of the gamma-subunit of the GlcNAc-1-phosphotransferase complex for selective mannose 6-phosphate modifications on lysosomal enzymes“

    Logo SFB877


    07/2010 - 06/2022

    Sandra Pohl & Thomas Braulke
    German Research Foundation (DFG)
    Collaborative Research Centre 877:
    "Proteolysis as a Regulatory Event in Pathophysiology"
    www.uni-kiel.de/Biochemie/sfb877/

    Concluded funding

    Logo ISMRD

    03/2017 - 02/2018
    Sandra Pohl
    ISMRD - International Society for Mannosidosis & Related Diseases (USA)
    "Osteoporosis in Mucolipidosis II - A potential corrective approach"
    http://www.ismrd.org/research

    Logo GRK1459

    05/2008 - 04/2017
    Thomas Braulke (Speaker+ Coordinator),
    Sandra Pohl & Stephan Storch
    German Research Foundation (DFG)
    Research Training Group 1459:
    "Sorting and Interactions between Proteins of
    Subcellular Compartments"
    www.grk1459.de