The pharmacological chaperone N-n-butyl-deoxygalactonojirimycin enhances β-galactosidase processing and activity in fibroblasts of a patient with infantile GM1-gangliosidosis

Hum Genet. 2020 May;139(5):657-673. doi: 10.1007/s00439-020-02153-3. Epub 2020 Mar 26.

Abstract

GM1-gangliosidosis, a lysosomal storage disorder, is associated with ~ 161 missense variants in the GLB1 gene. Affected patients present with β-galactosidase (β-Gal) deficiency in lysosomes. Loss of function in ER-retained misfolded enzymes with missense variants is often due to subcellular mislocalization. Deoxygalactonojirimycin (DGJ) and its derivatives are pharmaceutical chaperones that directly bind to mutated β-Gal in the ER promoting its folding and trafficking to lysosomes and thus enhancing its activity. An Emirati child has been diagnosed with infantile GM1-gangliosidosis carrying the reported p.D151Y variant. We show that p.D151Y β-Gal in patient's fibroblasts retained < 1% residual activity due to impaired processing and trafficking. The amino acid substitution significantly affected the enzyme conformation; however, p.D151Y β-Gal was amenable for partial rescue in the presence of glycerol or at reduced temperature where activity was enhanced with ~ 2.3 and 7 folds, respectively. The butyl (NB-DGJ) and nonyl (NN-DGJ) derivatives of DGJ chaperoning function were evaluated by measuring their IC50s and ability to stabilize the wild-type β-Gal against thermal degradation. Although NN-DGJ showed higher affinity to β-Gal, it did not show a significant enhancement in p.D151Y β-Gal activity. However, NB-DGJ promoted p.D151Y β-Gal maturation and enhanced its activity up to ~ 4.5% of control activity within 24 h which was significantly increased to ~ 10% within 6 days. NB-DGJ enhancement effect was sustained over 3 days after washing it out from culture media. We therefore conclude that NB-DGJ might be a promising therapeutic chemical chaperone in infantile GM1 amenable variants and therefore warrants further analysis for its clinical applications.

Publication types

  • Case Reports

MeSH terms

  • 1-Deoxynojirimycin / chemistry
  • 1-Deoxynojirimycin / pharmacology*
  • Child, Preschool
  • Endoplasmic Reticulum Stress / drug effects
  • Enzyme Inhibitors / chemistry
  • Enzyme Inhibitors / pharmacology
  • Fibroblasts / drug effects
  • Fibroblasts / metabolism*
  • Fibroblasts / pathology
  • Gangliosidosis, GM1 / drug therapy
  • Gangliosidosis, GM1 / metabolism*
  • Gangliosidosis, GM1 / pathology
  • Humans
  • Lysosomes / drug effects
  • Lysosomes / metabolism
  • Lysosomes / pathology
  • Male
  • Molecular Chaperones / pharmacology
  • Mutant Proteins / chemistry
  • Mutant Proteins / genetics
  • Mutant Proteins / metabolism*
  • Mutation*
  • Protein Conformation
  • Protein Processing, Post-Translational / drug effects*
  • Protein Transport
  • beta-Galactosidase / chemistry
  • beta-Galactosidase / genetics
  • beta-Galactosidase / metabolism*

Substances

  • Enzyme Inhibitors
  • Molecular Chaperones
  • Mutant Proteins
  • 1-Deoxynojirimycin
  • GLB1 protein, human
  • beta-Galactosidase