Enzymes involved in mammalian oligosaccharide biosynthesis

Several new sialyltransferases, N-acetylgalactosaminyltransferase and fucosyltransferase genes have been reported in this past year. These sequences have advanced our understanding of the structural, functional and evolutionary relationships amongst the glycosyltransferases, including their roles in selectin ligand biosynthesis. Ablation of the murine N-acetylgalactosaminyltransferase 1 gene through gene `knock out' technology has yielded insight into the role of this gene in the developing mouse. Novel `O-linked' protein glycosylation events described in the past year have added to the substantial known diversity in the oligosaccharide structure and glycosyltransferase repertoire of mammalian organisms.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31305/1/0000211.pd

Characterisation of N-glycans in the epithelial-like tissue of the rat cochlea

Nonomura Y., Sawamura S., Hanzawa K., et al. Characterisation of N-glycans in the epithelial-like tissue of the rat cochlea. Scientific Reports 9, 1551 (2019); https://doi.org/10.1038/s41598-018-38079-0.Membrane proteins (such as ion channels, transporters, and receptors) and secreted proteins are essential for cellular activities. N-linked glycosylation is involved in stability and function of these proteins and occurs at Asn residues. In several organs, profiles of N-glycans have been determined by comprehensive analyses. Nevertheless, the cochlea of the mammalian inner ear, a tiny organ mediating hearing, has yet to be examined. Here, we focused on the stria vascularis, an epithelial-like tissue in the cochlea, and characterised N-glycans by liquid chromatography with mass spectrometry. This hypervascular tissue not only expresses several ion transporters and channels to control the electrochemical balance in the cochlea but also harbours different transporters and receptors that maintain structure and activity of the organ. Seventy-nine N-linked glycans were identified in the rat stria vascularis. Among these, in 55 glycans, the complete structures were determined; in the other 24 species, partial glycosidic linkage patterns and full profiles of the monosaccharide composition were identified. In the process of characterisation, several sialylated glycans were subjected sequentially to two different alkylamidation reactions; this derivatisation helped to distinguish α2,3-linkage and α2,6-linkage sialyl isomers with mass spectrometry. These data should accelerate elucidation of the molecular architecture of the cochlea

Improved Method for Drawing of a Glycan Map, and the First Page of Glycan Atlas, Which Is a Compilation of Glycan Maps for a Whole Organism

<div><p>Glycan Atlas is a set of glycan maps over the whole body of an organism. The glycan map that includes data of glycan structure and quantity displays micro-heterogeneity of the glycans in a tissue, an organ, or cells. The two-dimensional glycan mapping is widely used for structure analysis of <i>N</i>-linked oligosaccharides on glycoproteins. In this study we developed a comprehensive method for the mapping of both <i>N</i>- and <i>O</i>-glycans with and without sialic acid. The mapping data of 150 standard pyridylaminated glycans were collected. The empirical additivity rule which was proposed in former reports was able to adapt for this extended glycan map. The adapted rule is that the elution time of pyridylamino glycans on high performance liquid chromatography (HPLC) is expected to be the simple sum of the partial elution times assigned to each monosaccharide residue. The comprehensive mapping method developed in this study is a powerful tool for describing the micro-heterogeneity of the glycans. Furthermore, we prepared 42 pyridylamino (PA-) glycans from human serum and were able to draw the map of human serum <i>N</i>- and <i>O</i>-glycans as an initial step of Glycan Atlas editing.</p></div

Glycan map of 150 standard glycans.

<p>White and black circles are <i>N</i>-linked and <i>O</i>-linked glycans, respectively. Data used for the plotting are listed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0102219#pone.0102219.s001" target="_blank">Table S1</a>.</p

MS/MS analysis of desialylated A2-5b.

<p>Parent ion (<i>m/z</i> 2252.887) was subjected to positive-mode MS/MS. Selected characteristic fragment ions are annotated and compatible structures are shown. Circles indicate hexose, and squares are <i>N</i>-acetylhexosamine. The fragment ions including pyridylamino residue are estimated to be derivatives from reducing end.</p

Partial elution times of sugar residues of <i>N</i>-glycan on a reversed phase HPLC.

<p>Partial elution time of each residue is written using symbols for the different types of monosaccharides. Circles indicate hexose, squares are GlcNAc, triangles are Fuc, the star is Xyl, and diamonds are NeuAc. Underlined letters are the residues, and the type of monosaccharides are followed: GN, GlcNAc; M, Man; G, Gal; X, Xyl; F, Fuc; Gc, Glc; S, NeuAc; BS, bisecting GlcNAc; CH, GlcNAc in <i>N,N′</i>-diacetylchitobiose core. The residues, X, GN3, GN4, and GN5 have two or three partial elution times corresponding to another specific residue. For example, the partial elution time of residue X is 4.7 when M2 residue exists and −0.5 when M2 is absent.</p