Insulin (INS)

Insulin (abbreviation: INS) is a protein hormone secreted by pancreatic β-cells in the pancreas stimulated by endogenous or exogenous substances such as glucose, lactose, ribose, arginine, glucagon, etc. The molecular weight of insulin is 5,700. insulin consists of two peptide chains, A and B. Insulin Human has 11 kinds of 21 amino acids in the A chain and 15 kinds of 30 amino acids in the B chain, totaling 51 amino acids. The sulfhydryl groups in the four cysteines A7(Cys)-B7(Cys) and A20(Cys)-B19(Cys) form two disulfide bonds, connecting the A and B chains. In addition a disulfide bond exists between A6(Cys) and A11(Cys) in the A chain. It is secreted into the bloodstream as an equal molecule with C peptide, and its biosynthesis rate is affected by plasma glucose concentration. When blood glucose concentration rises, the insulinogen content of β-cells increases and insulin synthesis is accelerated. Insulin is the only hormone in the body that lowers blood glucose while promoting glycogen, fat and protein synthesis.

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Biological function of INS

The role of insulin on glucose metabolism: accelerate the entry of glucose into cells through transporters; promote the utilization of sugar in the body; promote glycogen synthesis and inhibit glycogenolysis; promote the conversion of glucose into fat and protein; inhibit glucose anabolism. Under normal conditions, insulin secreted by the pancreas binds to the Insulin receptor on the cell surface and activates the insulin signaling pathway to promote glucose utilization and glycogen synthesis, thereby lowering blood glucose. In diabetes, cells develop insulin resistance (IR), which decreases the efficiency of insulin in promoting glucose uptake and utilization, resulting in increased blood glucose concentrations. type 1 diabetes is characterized by an inability to synthesize insulin, while type 2 diabetes is characterized by an inability to synthesize insulin, which is probably due to a defect in the insulin signaling pathway.

Figure 2 Molecular structure of INS

Molecular mechanism of INS

The insulin receptor is a tyrosine protein kinase (PTK)-type receptor. Binding of insulin to its receptor rapidly leads to a conformational change that activates the tyrosine kinase structural domain of the receptor's β-subunit. Insulin receptor substrate IRS: (1) Activation of IRS protein can recruit and activate a variety of signaling proteins, mediating IRS multidirectional cell signaling effects, avoiding direct recruitment of SH2-like proteins to its own phosphorylation site by a variety of receptors, and therefore is an economical and effective way of cell signaling. (2) Tyrosine phosphorylation of the β-subunit, with the participation of insulin receptor substrate 1/2 (IRS-1/2), binds to Grb2 and PI3K in the SH2-containing region, which then activates signaling pathways, such as PI3K and Ras-Raf-MEK-MAPK. pathway of PI3K: activated PI3K pathway: activated IRS binds to the SH2 structural domain of the regulatory subunit of PI3K, p85, and thus activates the catalytic subunit of PI3K, p110. the metabolic function of insulin is mainly through this pathway. after PI3K activation. PI3K activation leads to the production of PIP, PIP2, or phosphatidylinositol trisphosphate (PIP3), which are considered to be the second messengers of insulin and other growth factors, and bind to downstream molecules containing the PH region to transmit signals downstream. pKB, a signaling molecule downstream of PI3K, can be activated by the phosphorylation of PDK1 and PDK2, and is the key molecule in the PI3K pathway, which can produce a variety of biological effects, such as glycogen synthesis, protein synthesis, and protein synthesis. PKB is a key molecule in the PI3K pathway, which can produce a variety of biological effects, such as glycogen synthesis, protein synthesis, glucose transport, anti-lipolysis, inhibition of apoptosis, etc, and mediate the survival pathway of β-cells, which is closely related to β-cell growth, proliferation, differentiation, and apoptosis, etc. PKB also promotes the translocation of the grapheme transporters, GLUT-1 and GLUT-4, to the cell membrane for the uptake of glucose.

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