Abstract
Oligosaccharides of glycoproteins expressed on the cell surface play important roles in cell-cell interactions, particularly sialylated N-glycans having a negative charge, which interact with sialic acid-binding immunoglobulin-like lectins (siglecs). The entire structure of sialylated N-glycans expressed in the mouse brain, particularly the linkage type of sialic acid residues attached to the backbone N-glycans, has not yet been elucidated. An improved method to analyze pyridylaminated sugar chains using high performance liquid chromatography (HPLC) was developed to determine the entire structure of sialylated N-linked sugar chains expressed in the adult and developing mouse cerebral cortices. Three classes of sialylated sugar chains were prevalent: 1) N-glycans containing α(2-3)-sialyl linkages on a type 2 antennary (Galβ(1-4)GlcNAc), 2) sialylated N-glycans with α(2-6)-sialyl linkages on a type 2 antennary, and 3) a branched sialylated N-glycan with a [Galβ(1-3){NeuAcα(2-6)}GlcNAc-] structure, which was absent at embryonic day 12 but then increased during development. This branched type sialylated N-glycan structure comprised approximately 2 % of the total N-glycans in the adult brain. Some N-glycans (containing type 2 antennary) were found to change their type of sialic acid linkage from α(2-6)-Gal to α(2-3)-Gal. Thus, the linkages and expression levels of sialylated N-glycans change dramatically during brain development.Electronic supplementary materialThe online version of this article (doi:10.1007/s10719-014-9566-2) contains supplementary material, which is available to authorized users.
Highlights
Sugar chains envelop the vast majority of the cell surface and are considered to play significant roles in cell-cell and extracellular matrix interactions as mediators and as signal transducers
40 % of total N-glycan is sialylated and approximately 10 % of these N-glycans carry polysialic acids (PSA), which are partly comprised of PSA on neural cell adhesion molecules (N-CAM) [8]
After neuraminidase treatment the galactosidase-reaction product was analyzed by 2D-high-performance liquid chromatography (HPLC) mapping and was found to be identical to A2G0F (Fig. 6). These results demonstrate that sialic acids were not attached to the terminal galactose residues of the sialylated N-glycan
Summary
Sugar chains envelop the vast majority of the cell surface and are considered to play significant roles in cell-cell and extracellular matrix interactions as mediators and as signal transducers. Myelin-associated glycoprotein (MAG), a member of the siglecs recognizing α(2-3)-sialic acid, is involved in myelin formation, and in myelin maintenance [17]. It has received particular attention because it enhances in vitro neurite outgrowth at early developmental stages but inhibits neurite outgrowth in adults [18]. It is extremely important to determine the structure of sialic acid-containing sugar chains in the adult brain as well as changes in glycosylation during development to understand the significance of interactions between siglecs and sialic acidcontaining sugar chains. We aimed to identify sialylated N-glycans whose expression levels vary dramatically during brain development
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