Glycosylation peptide synthesis

Glycosylation

Glycosylation is the process by which a protein or lipid is attached to a sugar under the control of an enzyme and occurs in the endoplasmic reticulum. The sugar is transferred to the protein by the action of a glycosyltransferase, and the amino acid residue on the protein forms a glycosidic bond. The protein undergoes glycosylation to form glycoproteins. Glycosylation is an important modification of proteins and regulates protein function.

process

N-linked sugar chain synthesis begins in the endoplasmic reticulum and is completed in the Golgi apparatus. The glycoprotein formed in the endoplasmic reticulum has a similar sugar chain. After the Cis surface enters the Golgi apparatus, a series of ordered processing and modification occurs during the transport between the membrane capsules. The original sugar chain is large. Part of the mannose is excised, but a variety of glycosyltransferases are sequentially added with different types of sugar molecules to form oligosaccharide chains with different structures. The spatial structure of the glycoprotein determines that it can bind to that glycosyltransferase and undergo specific glycosylation modifications.
Many glycoproteins have both N-linked sugar chains and O-linked sugar chains. O-linked glycosylation is carried out in the Golgi apparatus. Usually, the first attached sugar unit is N-acetylgalactose, and the linked sites are the hydroxyl groups of Ser, Thr and Hyp, and then the glycosyl groups are successively transferred to form. Oligosaccharide chains, sugar donors are also nucleoside sugars, such as UDP-galactose. The result of glycosylation allows different proteins to be labeled differently, altering the conformation of the polypeptide and increasing the stability of the protein.
One or more aminoglycan chains can also be attached to the serine residue of the core protein via xylose on the Golgi to form proteoglycans. Some of these proteins are secreted outside the cell to form an extracellular matrix or mucus layer, some anchored to the membrane.

classification

According to the type of glycoside chain, protein glycosylation can be divided into four types, that is, the hydroxyl group of serine, threonine, hydroxylysine and hydroxyproline is used as a point of connection to form an -O-glycosidic bond. Using an amide group of asparagine, an α-amino group of an N-terminal amino acid, and an ω-amino group of lysine or arginine as a point of attachment to form an -N-glycosidic bond; aspartic acid or glutamic acid The free carboxyl group is a point of attachment, forming a lipotypic bond type and a glycopeptide bond with cysteine ​​as a point of attachment.


Peptide

Polypeptides are compounds in which alpha-amino acids are linked together by peptide bonds and are also intermediates in protein hydrolysis.
Generally, the number of amino acids contained in the peptide is two to nine. According to the number of amino acids in the peptide, the peptide has various different names: a compound obtained by dehydration condensation of two amino acid molecules is called a dipeptide, and the analogy is analogous. Peptides, tetrapeptides, pentapeptides, etc., up to the nonapeptide. Compounds usually dehydrated and condensed from 10 to 100 amino acid molecules are called polypeptides. Their molecular weights are less than 10,000 Da (Dalton, Dalton), and they can pass through the semipermeable membrane and are not precipitated by trichloroacetic acid and ammonium sulfate. There are also literatures that refer to peptides consisting of 2 to 10 amino acids as oligopeptides (small peptides); peptides of 10 to 50 amino acids are called peptides; peptides composed of more than 50 amino acids are called proteins, in other words, Protein is sometimes referred to as a polypeptide. Polypeptides, also referred to as peptides, were discovered in the 20th century.

Classification of peptides

The polypeptide has two kinds of biologically active polypeptides and artificial synthetic polypeptides.

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