Amylin-A kind of peptide associated with diabetes

Amylin, or Islet Amyloid Polypeptide (IAPP), is a 37-residue peptide hormone.[1] It is cosecreted with insulin from the pancreatic β-cells in the ratio of approximately 100:1. Amylin plays a role in glycemic regulation by slowing gastric emptying and promoting satiety, thereby preventing post-prandial spikes in blood glucose levels.

IAPP is processed from an 89-residue coding sequence. Proislet Amyloid Polypeptide (proIAPP,Proamylin, Proislet Protein) is produced in the pancreatic beta cells (β-cells) as a 67 amino acid, 7404 Dalton pro-peptide and undergoes post-translational modifications including protease cleavage to produce amylin.[2]

The human form of IAPP has the amino acid sequence KCNTATCATQRLANFLVHSSNNFGAILSSTNVGSNTY, with a disulfide bridge between cysteine residues 2 and 7. Both the amidated C-terminus and the disulfide bridge are necessary for the full biological activity of amylin. IAPP is capable of forming amyloid fibrils in vitro. Within the fibrillization reaction, the early prefibrillar structures are extremely toxic to beta-cell and insuloma cell cultures.[2] Later amyloid fiber structures also seem to have some cytotoxic effect on cell cultures. Studies have shown that fibrils are the end product and not necessarily the most toxic form of amyloid proteins/peptides in general. A non-fibril forming peptide (1-19 residues of human amylin) is toxic like the full-length peptide but the respective segment of rat amylin is not. It was also demonstrated by solid-state NMR spectroscopy that the fragment 20-29 of the human-amylin fragments membranes. Rats and mice have six substitutions (three of which are proline substitions at positions 25, 28 and 29) that are believed to prevent the formation of amyloid fibrils. Rat IAPP is nontoxic to beta-cells, even when overexpressed.

Amylin functions as part of the endocrine pancreas and contributes to glycemic control. The peptide is secreted from the pancreatic islets into the blood circulation and is cleared by peptidases in the kidney. It is not found in the urine.

Amylin’s metabolic function is well-characterized as an inhibitor of the appearance of nutrient [especially glucose] in the plasma. It thus functions as a synergistic partner to insulin, with which it is cosecreted from pancreatic beta cells in response to meals. The overall effect is to slow the rate of appearance (Ra) of glucose in the blood after eating; this is accomplished via coordinate slowing down gastric emptying, inhibition of digestive secretion [gastric acid, pancreatic enzymes, and bile ejection], and a resulting reduction in food intake. Appearance of new glucose in the blood is reduced by inhibiting secretion of the gluconeogenic hormone glucagon. These actions, which are mostly carried out via a glucose-sensitive part of the brain stem, the area postrema, may be over-ridden during hypoglycemia. They collectively reduce the total insulin demand.

Amylin also acts in bone metabolism, along with the related peptides calcitonin and calcitonin gene related peptide.

Rodent amylin knockouts are known to fail to achieve the normal anorexia following food consumption. Because it is an amidated peptide, like many neuropeptides, it is believed to be responsible for the anorectic effect. A synthetic analog of human amylin with proline substitutions in positions 25, 26 and 29, or pramlintide (brand name Symlin), was recently approved for adult use in patients with both diabetes mellitus type 1 and diabetes mellitus type 2. Insulin and pramlintide, injected separately but both before a meal, work together to control the post-prandial glucose excursion.[3]

Amylin is degraded in part by insulin-degrading enzyme.

Karebay can synthetic amylin with Cyanine or other fluorescent moleculars , so that scientists can knew more details about its molecular mechanism.

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Reference [1] Qi D, Cai K, Wang O,et al. Le (January 2010). “Fatty acids induce amylin expression and secretion by pancreatic beta-cells”. Am. J. Physiol. Endocrinol. Metab. 298 (1): E99–E107. [2] Brender JR, Lee EL, Cavitt MA, et al. (May 2008). “Amyloid fiber formation and membrane disruption are separate processes localized in two distinct regions of IAPP, the type-2-diabetes-related peptide”. J. Am. Chem. Soc. 130 (20): 6424–9. [3] Amylin Pharmaceuticals, Inc. 2006. Archived from the original on 13 June 2008. Retrieved 2008-05-28.

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