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Profiling on various kinds of glycan

The first: glycolipid

Glycolipids are lipid compounds containing ester compounds, a class of amphiphilic molecules that widely exist in organisms.

Classification:

According to the lipid component, lipids can be divided into four types:

(1) glycosphingolipid containing sphingosine;

(2) glycosylacylglycerid containing grease;

(3) glycolipids derived from dolichol phosphate;

(4) steroid-derived glycolipids

Let’s focus on glycosylacylglycerid and glycosphingolipid next. Glycosylacylglycerid’s sugar base structure is similar to phosphatide acyl glycerin, main chain is glycerin, containing the fatty acids, but not the chemical compounds such as phosphorous and choline. Glycerol lipids have many biological traits, such as antioxidant, antiviral, antibacterial, anti-tumor, anti-inflammation, anti-atherosclerosis and so on, and are found in nerve tissues, plants and microorganisms of animals

Glycosphingolipids are derived from ceramides. The fatty acids are attached to the c-2 amino group of the long chain of sphingoamol. Glycosphingolipids containing one or more neutral glycosyls as polar heads are called neutral glycosphingolipids. As a component of cell membrane, glycolipids play an important role in cell adhesion, growth, differentiation, signaling and other processes. It’s also meaningful for glycomic profiling.

The second: N-glycan

As for N-glycan profiling, it’s necessary to introduce N-linked glycosylation consists of N- sugar synthesis, transfer and modification. It is a co-translation or post-translational modification of a new peptide chain by which the sugar chain passes a specific asparagine. So this glycosylation is called N- glycosylation. The process of N- glycosylation was performed in Endoplasmic reticulum (ER) and Golgi apparatus (GA).

Synthesis: The synthesis of N – sugar began in endoplasm omentum cytoplasmic side, formed after the dolichol phosphorylation activation state. Under the action of the glycosyl transferase ALG7 and ALG13/14, GlcNAc link to the dolichol. Then after the ALG1, ALG2 and ALG11 plus the five mannose  molecules, through Flipase transferred to the endoplasmic reticulum cavity side. Under the action of a series of glycosyltransferases (ALG3, ALG9, ALG12, ALG9, ALG6, ALG8, ALG10) in the endoplasmic reticulum, a oligosaccharide chain with 2 molecules of n-acetylglucosamine, 9 molecules of mannose and 3 molecules of glucose was formed, thus, antenna structure of a, b and c three claws was formed

Transfer: N – glycan decoration is a part of the nascent peptide chain through oligosaccharide base transferase (oligosaccharyltransferase, OST) complex. The glycosyl transferase is a more complex, in yeast by Wbp1p, Stt3p, Ost1p, Swp1p, Ost1p, Ost4p, Ost5p and Ost3p/Ost6p, responsible for the synthesis of oligosaccharides in the chain transfer to the nascent peptide chain specific asparagine (N – X – S/T and X! = P). OST is relatively conservative in eukaryotes and has homologous proteins in mammalian cells and arabidopsis thaliana

Modification: Modification of the sugar chain in the endoplasmic reticulum involves the removal of the terminal 3 molecules of glucose

The terminal mannose of b branch and b branch, after entering the endoplasmic reticulum, forms n-sugar chain of complex type, hybrid type and high mannose type after cutting and processing various glycosyltransferases and glycosidases. In plants, complex sugars and hybrid sugars the second n-acetylglucosamine is also linked to a xylose, forming a complex n-sugar type characteristic of plants.

Function: According to the current research results, it can be determined that the N- glycosylation modification of protein plays an important role in the process of protein folding, transportation and other processes. More specific relevant studies on N-glycan analysis need to be further studied.

The third: O-Glycan

O-Glycan profiling is different from N-glycan profiling. O-linked glycosylation is the transfer of the sugar chain to the oxygen atoms of serine, threonine, or hydroxyl lysine of the polypeptide chain. O-linked glycosylation is catalyzed by different glycosyltransferases, with one monosaccharide added at a time. As with complex n-linked glycosylation, the final step is to add sialic acid residues, which occur in the golgi body anti-mask capsule and TGN.

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