title: Differential site accessibility mechanistically explains subcellular-specific N-glycosylation determinants.
abstract: Glycoproteins perform extra- and intracellular functions in innate and adaptive immunity by lectin-based interactions to exposed glyco-determinants. Herein, we document and mechanistically explain the formation of subcellular-specific N-glycosylation determinants on glycoproteins trafficking through the shared biosynthetic machinery of human cells. LC-MS/MS-based quantitative glycomics showed that the secreted glycoproteins of eight human breast epithelial cells displaying diverse geno- and phenotypes consistently displayed more processed, primarily complex type, N-glycans than the high-mannose-rich microsomal glycoproteins. Detailed subcellular glycome profiling of proteins derived from three breast cell lines (MCF7/MDA468/MCF10A) demonstrated that secreted glycoproteins displayed significantly more α-sialylation and α1,6-fucosylation, but less α-mannosylation, than both the intermediately glycan-processed cell-surface glycoproteomes and the under-processed microsomal glycoproteomes. Subcellular proteomics and gene ontology revealed substantial presence of endoplasmic reticulum resident glycoproteins in the microsomes and confirmed significant enrichment of secreted and cell-surface glycoproteins in the respective subcellular fractions. The solvent accessibility of the glycosylation sites on maturely folded proteins of the 100 most abundant putative N-glycoproteins observed uniquely in the three subcellular glycoproteomes correlated with the glycan type processing thereby mechanistically explaining the formation of subcellular-specific N-glycosylation. In conclusion, human cells have developed mechanisms to simultaneously and reproducibly generate subcellular-specific N-glycosylation using a shared biosynthetic machinery. This aspect of protein-specific glycosylation is important for structural and functional glycobiology and discussed here in the context of the spatio-temporal interaction of glyco-determinants with lectins central to infection and immunity.
authors.affiliation: Department of Chemistry and Biomolecular Sciences, Biomolecular Frontiers Research Centre, Macquarie University , Sydney, NSW , Australia.
authors.forename: Ling Yen
authors.initials: LY
authors.lastname: Lee
authors.affiliation: Department of Chemistry and Biomolecular Sciences, Biomolecular Frontiers Research Centre, Macquarie University , Sydney, NSW , Australia.
authors.forename: Chi-Hung
authors.initials: CH
authors.lastname: Lin
authors.affiliation: Department of Chemistry and Biomolecular Sciences, Biomolecular Frontiers Research Centre, Macquarie University , Sydney, NSW , Australia.
authors.forename: Susan
authors.initials: S
authors.lastname: Fanayan
authors.affiliation: Department of Chemistry and Biomolecular Sciences, Biomolecular Frontiers Research Centre, Macquarie University , Sydney, NSW , Australia.
authors.forename: Nicolle H
authors.initials: NH
authors.lastname: Packer
authors.affiliation: Department of Chemistry and Biomolecular Sciences, Biomolecular Frontiers Research Centre, Macquarie University , Sydney, NSW , Australia.
authors.forename: Morten
authors.initials: M
authors.lastname: Thaysen-Andersen
keywords: N-glycan; N-glycome; N-glycosylation; glycoprotein; glycoproteome; glycosylation site; solvent accessibility; subcellular location