Murine β-galactosidase stability is not dependent on temperature or protective protein/cathepsin A

GM1 gangliosidosis, a neurodegenerative disorder, and Morquio B disease, a skeletal disorder, are lysosomal storage disorders caused by inherited defects in the enzyme β-galactosidase (GLB1; EC 3.1.2.23; MIM #611458). Enzyme replacement therapy (ERT), a standard of care for a number of non-neuronopathic lysosomal storage disorders, is not yet available for GLB1 deficiency. Although functionally active recombinant human and feline GLB1 precursors have been purified, ERT has not yet been demonstrated in GM1 gangliosidosis or Morquio B disease models. A major obstacle to developing effective therapy may be the stability of human GLB1. We show here that mouse GLB1 has greater stability when compared to human GLB1, and that human GLB1 activity is temperature and protective-dependent on protein cathepsin A, while that of mouse GLB1 is not. These findings may impact on the eventual development of ERT for GLB1 deficiency. Despite our attempts to improve the extracellular stability of human GLB1 through sequence modification and the use of chemical chaperone N-butyldeoxygalactonojirimycin, the specific enzyme activity remained well below that of mGLB1.