Glycoprotein basic introduction

Glycoprotein is a complex oligosaccharide chain composed of branched oligosaccharide chains and polypeptide chains, It is widely present in the cell membrane, cell stroma, plasma and mucus. Glycoproteins in the sugar chain in the maintenance of protein stability, resistance to protease hydrolysis, to prevent antibody recognition and participation in peptide chain in the endoplasmic reticulum cascade start play an important role, with switching and tuning function, hormone function, intracellular transport function , Protect and promote the absorption of substances involved in blood clotting and cell recognition, for the regulation of proliferation, fertilization, occurrence, differentiation and immune phenomena such as life plays a very important role. The main chain is short, in most cases, the sugar content is less than the protein. In the glycoprotein, sugar composition is often more complex, mannose, galactose, fucose, glucosamine, galactosamine, sialic acid and so on. Oligosaccharides and proteins in two ways: (1) sugar hemiacetal hydroxyl and hydroxy-containing amino acids (serine, threonine, hydroxyl lysine, etc.) to O-glycosidic bond; (2) sugar half

The acetal hydroxyl groups and amide groups of asparagine are bound by N-glycosidic bonds. In the nature of the distribution is very extensive. Has been studied six or seven kinds of plasma proteins, the vast majority of glycoproteins. Some enzymes and hormones are glycoproteins. Glycoprotein is also an important component of cytoplasmic membrane, cell stroma, plasma mucus and so on. Glycoproteins are increasingly isolated from plants, particularly lectins. Many lectins have been isolated from vertebrates and invertebrates, and even from many microorganisms, and most of them are glycoproteins. Glycoproteins are species-specific. A protein is present in the form of glycoproteins in one animal, and in another animal. Even though they are glycoproteins, their sugar content may be different, such as cattle, sheep and pigs pancreatic ribonuclease are glycoprotein, but the sugar content was 9.4%, 9.8% and 38%; rats Of the enzyme is not sugar.

At the same time, glycoprotein is a binding protein, glycoprotein is short oligosaccharide chain and protein covalently connected molecules. Its overall nature is closer to the protein. Between the sugar and protein to protein-based, to a certain location

Covalent bonds are linked to a number of short oligosaccharide chains, which are often branched heteropolysaccharide chains and do not exhibit repeating disaccharide sequences, typically consisting of 2-10 monomers (less than 15) =, The end members are often sialic acid or L-fucose. Normally each molecule contains less sugar (about 4%). Some glycoproteins contain only one or several glycosyl groups, while others contain multiple linear or branched oligosaccharide side chains. Glycoprotein is usually secreted into the body fluid or membrane protein, which is located outside the cell, and a corresponding function. Glycoproteins include enzymes, hormones, carriers, lectins, antibodies, and the like. Α-D-xylose (Xyl) α-D-arabinose (Ara) α-D-galactose (Gal) α-D-mannose Acetylglucosamine (GlcNAG) N-Acetylgalactosamine (GalNAC) N-Acetylneuraminic acid (NeuNAC) Sialic acid (Sia) Glucosamine (GlcNAA).

The main types of glycoproteins

Corn protein spray: corn gluten meal, also known as corn bran, corn starch is used after the production of starch and embryo by-products, and then one of the protein, high energy corn pulp spray up, so that its protein, energy, amino acid content increased significantly , Widely used in the production of feed. Two features: 1, lower feed costs; 2, the color is good, mixed with a good color material. In addition, the palatability of this product is good, high absorption rate, high energy, 15 water within the corn energy 2500 cards, and the energy of this product in 1700 cards or so, and the price of this product is lower than the price of corn.

Glycoprotein No. 1: glycoprotein 1 instead of corn, reducing feed costs. This product is a subsidiary of corn in the process of sugar products. Contains corn flour 95%, 20% of bran, in addition to sugar, the corn contains protein and other nutrients are preserved. The energy is 1.7 times that of corn.

Glycoprotein 2: glycoprotein, also known as sugar residue is the starch plant in the process of sugar subsidiary products, is a pure plant products, sugar big palatability good animals like to eat good color. Protein in 17 or so fat in 20 or so, the price is much lower than corn. Can replace the corn or directly add, to stabilize the quality of feed to reduce feed costs.

Glycoprotein 3: Glycoprotein 3 has 16 proteins, about 20 fat.

The main function of glycoprotein

Carrying information on the fate of protein metabolism

The sialic acid residue at the end of a glycoprotein oligosaccharide chain determines the presence or absence of a protein in the bloodstream.

A. ceruloplasmin in vertebrate blood. Liver cells can degrade ceruloplasmin, which has lost sialic acid, and the elimination of sialic acid may be one of the ways of labeling "old" proteins in vivo.

B. Red blood cells. The content of sialic acid in the nascent red blood cell membrane is much higher than that of the mature erythrocyte membrane. Treatment of the new red blood cells with sialidase, re-injection of the body, all disappeared after a few hours. While the enzyme treatment of red blood cells, re-injection a few days later, still in the normal survival of the body.

The key role of oligosaccharide chain

Normal lymphocytes should be homing to the spleen, and cut sialic acid, the results even homing to the liver. In the prokaryotic expression of eukaryotic genes, can not be glycosylated.

Glycoproteins may be cytolytic or membrane-bound, and may be present in the cell or present in the cell matrix. Glycoprotein is more typical in animals and plants, glycoprotein is particularly abundant in spine, such as metal transporter (transferrin), blood ceruloplasmin, coagulation factors, complement system, some hormones, Follicle-stimulating hormone (FSH, RNase, membrane-bound proteins (such as Na + -K + -ATPase in animal cell membranes), major histocompatibility antigens (major histocompatibility antigens) that mediate donor-organ systems on the surface of cells Cross-matching with the recipient organism). The vast majority of glycoprotein oligosaccharides are glycoprotein functional centers. Some glycoproteins of the sugar itself or the body of the glycoprotein play a protective effect or lubrication, such as cattle RNaseB (glycoprotein) resistance to heat than RNaseA, a large number of sialic acid can enhance the viscosity of salivary mucin and thus enhance the saliva Lubricity. Antarctic fish antifreeze protein sugar composition and water-type hydrogen bonds, to prevent the formation of ice products to improve the frost resistance. Glycoproteins play a more complex role in cell-to-cell signal transduction. Hiv's target cell-binding protein, GP120, is a glycoprotein that binds to the CD4 receptors on the surface of human target cells to attach to the surface of the target cell. If the sugar moiety of GP120 is removed, it can not bind to the CD4 receptor and lose its ability to infect. Cellular glycoproteins form glycocalyxes of the cell and participate in cell adhesion, which plays a key role in embryo and tissue growth, development, and differentiation.