The terms glycans and polysaccharides are defined by IUPAC as synonyms meaning "compounds consisting of a large number of monosaccharides linked glycosidically".
N-Linked glycans are attached in the endoplasmic reticulum to the nitrogen (N) in the side chain of asparagine (Asn) in the sequon.
At this point, the partially finished core glycan is flipped across the endoplasmic reticulum membrane, so that it is now located within the reticular lumen.
Following full assembly, the glycan is transferred en bloc by the glycosyltransferase oligosaccharyltransferase to a nascent peptide chain, within the reticular lumen.
Chaperone proteins in the endoplasmic reticulum, such as calnexin and calreticulin, bind to the three glucose residues present on the core N-linked glycan.
Therefore, the presence of a N-linked glycan allows the cell to control which cysteine residues will form disulfide bonds.
[3] Glycans may also be involved in "self" and "non self" discrimination, which may be relevant to the pathophysiology of various autoimmune diseases;[3] including rheumatoid arthritis [4] and type 1 diabetes.
In eukaryotes, O-linked glycans are assembled one sugar at a time on a serine or threonine residue of a peptide chain in the Golgi apparatus.
P-selectin binds to the SLex structure that is present on neutrophils in the bloodstream and helps to mediate the extravasation of these cells into the surrounding tissue during infection.
These comprise 2-aminosugars linked in an alternating fashion with uronic acids, and include polymers such as heparin, heparan sulfate, chondroitin, keratan and dermatan.
Some glycosaminoglycans, such as heparan sulfate, are found attached to the cell surface, where they are linked through a tetrasacharide linker via a xylosyl residue to a protein (forming a glycoprotein or proteoglycan).
A 2012 report from the U.S. National Research Council calls for a new focus on glycoscience, a field that explores the structures and functions of glycans and promises great advances in areas as diverse as medicine, energy generation, and materials science.
[6] Until now, glycans have received little attention from the research community due to a lack of tools to probe their often complex structures and properties.
[7] The report presents a roadmap for transforming glycoscience from a field dominated by specialists to a widely studied and integrated discipline.
As of 2019, NHLBI has established a new national career development consortium for excellence in glycoscience, led by program director Karin Hoffmeister.
[12] A large variety of different labels were introduced in the recent years, where 2-aminobenzamide (AB), anthranilic acid (AA), 2-aminopyridin (PA), 2-aminoacridone (AMAC) and 3-(acetylamino)-6-aminoacridine (AA-Ac) are just a few of them.
Fractionated glycans from high-performance liquid chromatography (HPLC) instruments can be further analyzed by MALDI-TOF-MS(MS) to get further information about structure and purity.
By choosing porous graphitic carbon as a stationary phase for liquid chromatography, even non derivatized glycans can be analyzed.
[16][17][18] Although MRM has been used extensively in metabolomics and proteomics, its high sensitivity and linear response over a wide dynamic range make it especially suited for glycan biomarker research and discovery.
This method uses either naturally occurring lectins or artificial monoclonal antibodies, where both are immobilized on a certain chip and incubated with a fluorescent glycoprotein sample.