title: Protective protein/cathepsin A rescues N-glycosylation defects in neuraminidase-1.
abstract: BACKGROUND
  Neuraminidase-1 (NEU1) catabolizes the hydrolysis of sialic acids from sialo-glycoconjugates. NEU1 depends on its interaction with the protective protein/cathepsin A (PPCA) for lysosomal compartmentalization and catalytic activation. Murine NEU1 contains 4 N-glycosylation sites, 3 of which are conserved in the human enzyme. The expression of NEU1 gives rise to differentially glycosylated proteins.
  
  
  METHODS
  We generated single-point mutations in mouse NEU1 at each of the 4 N-glycosylation sites. Mutant enzymes were expressed in NEU1-deficient cells in the presence and absence of PPCA.
  
  
  RESULTS
  All 4 N-glycosylation variants were targeted to the lysosomal/endosomal compartment. All N-glycans, with the exception of the most C-terminal glycan, were important for maintaining stability or catalytic activity. The loss of catalytic activity caused by the deletion of the second N-glycan was rescued by increasing PPCA expression. Similar results were obtained with a human NEU1 N-glycosylation mutant identified in a sialidosis patient. The N-terminal N-glycan of NEU1 is indispensable for its function, whereas the C-terminal N-glycan appears to be non-essential. The omission of the second N-glycan can be compensated for by upregulating the expression of PPCA.
  
  
  CONCLUSIONS
  These findings could be relevant for the design of target therapies for patients carrying specific NEU1 mutations.
authors.affiliation: Department of Genetics and Tumor Cell Biology, St. Jude Children's Research Hospital, Memphis, TN 38105-2794, USA.
authors.forename: Dongning
authors.initials: D
authors.lastname: Wang
authors.forename: Slava
authors.initials: S
authors.lastname: Zaitsev
authors.forename: Garry
authors.initials: G
authors.lastname: Taylor
authors.forename: Alessandra
authors.initials: A
authors.lastname: d'Azzo
authors.forename: Erik
authors.initials: E
authors.lastname: Bonten
mesh_terms: D000818:Animals; D043402:Cathepsin A / Q000235:genetics / Q000502:physiology*; D006031:Glycosylation; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D009081:Mucolipidoses / Q000235:genetics / Q000628:therapy; D020125:Mutation, Missense; D009439:Neuraminidase / Q000235:genetics*; D017354:Point Mutation; D017386:Sequence Homology, Amino Acid
chemical_list: D009439:Neuraminidase; C468629:CTSA protein, human; C543471:CTSA protein, mouse; D043402:Cathepsin A