Protective protein/cathepsin A rescues N-glycosylation defects in neuraminidase-1

• Published in: Biochimica et biophysica acta Vol. 1790; no. 4; pp. 275 - 282
• Main Authors: Wang, Dongning, Zaitsev, Slava, Taylor, Garry, d'Azzo, Alessandra, Bonten, Erik
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.04.2009
• Subjects: Animals; Cathepsin A - genetics; Cathepsin A - physiology; Chaperone therapy; Glycosylation; Humans; Mice; Models, Molecular; Mucolipidoses - genetics; Mucolipidoses - therapy; Mutation, Missense; NEU1; Neuraminidase; Neuraminidase - genetics; Point Mutation; Protective protein/cathepsin A; Sequence Homology, Amino Acid; Sialidase; Sialidosis; N, asparagine NEU1; YFP; D; DTT; Glycosylation; FACS; GFP; DMEM; Chaperone therapy; FBS; Neuraminidase; NEU1; PPCA; LSD; Sialidosis; PCR; Sialidase; Protective protein/cathepsin A
• ISSN: 0304-4165; 0006-3002; 1872-8006
• DOI: 10.1016/j.bbagen.2009.01.006

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. 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. 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. These findings could be relevant for the design of target therapies for patients carrying specific NEU1 mutations.