Title : Human
alpha-N-acetylgalactosaminidase :
site occupancy and structure of
N-linked oligosaccharides
Abstract :
- Human alpha-N-acetylgalactosaminidase (alpha-GalNAc; also known as alpha-galactosidase B ) is the lysosomal exoglycohydrolase that cleaves alpha-N-acetylgalactosaminyl moieties in glycoconjugates
- Mutagenesis studies indicated that the first five ( N124, N177, N201, N359, and N385 ) of the six potential N-glycosylation sites were occupied
- Site 3 occupancy was important for enzyme function and stability
- Characterization of the N-linked oligosaccharide structures on the secreted enzyme overexpressed in Chinese hamster ovary cells revealed highly heterogeneous structures consisting of complex (approximately 53%), hybrid (approximately 12%), and high mannose-type (approximately 33%) oligosaccharides
- The complex structures were mono-, bi-, 2,4-tri-, 2,6-tri-, and tetraantennary, among which the biantennary structures were most predominant (approximately 53%)
- Approximately 80% of the complex oligo-saccharides had a core-region fucose and 50% of the complex oligosaccharides were sialylated exclusively with alpha-2,3-linked sialic acid residues.
- The majority of hybrid type oligo-saccharides were GalGlcNAcMan(6)GlcNAc-Fuc(0-1)GlcNAc.
- Approximately 54% of the hybrid oligosaccharide were phosphorylated and one-third of these structures were further sialylated, the latter representing unique phosphorylated and sialylated structures
- Of the high mannose oligosaccharides, Man(5-7)GlcNAc(2) were the predominant species (approximately 90%) and about 50% of the high mannose oligosaccharides were phosphorylated, exclusively as monoesters whose positions were determined
- Comparison of the oligosaccharide structures of alpha-GalNAc and alpha-galactosidase A , an evolutionary-related and highly homologous exoglycosidase , indicated that alpha-GalNAc had more completed complex chains , presumably due to differences in enzyme structure/domains , rate of biosynthesis, and/or aggregation of the overexpressed recombinant enzymes