Discovery
AMY is a peptide hormone predominantly cosecreted with
insulin from pancreatic β cells. It aggregates to form an islet
amyloid in type 2 diabetes. The deposition of an amyloid in the islets of Langerhans in type 2 diabetes has been observed, and was
described as hyalinization in 1901. The genuine nature
of the human pancreatic islet amyloid was described as
AMY or IAPP by two independent groups in 1987.
Gene, mRNA, and precursor
The human AMY gene (IAPP), located on chromosome
12 (12p12.1), consists of three exons and is regulated by a
transcription factor, PDX-1. Human AMY mRNA has
1992 bp. The gene structure and its mRNA size are well
conserved among vertebrates. Mammalian IAPP is expressed in islet β cells, δ cells,
the gastrointestinal tract, and sensory neurons. In teleosts, iapp transcripts are detected and are found in the
optic tectum, hypothalamus, posterior brain, and testis
of goldfish.
Receptors
The functional receptors for AMY are generated from
the calcitonin receptor (CTR) in a complex with one of the
three receptor activity-modifying proteins (RAMP)-1, -2,
or -3. The CTR/RAMP1 and CTR/RAMP3 complexes
appear to be the dominant AMY receptors, judging by
the binding affinity. AMY also binds to CTR without
RAMPs, but the affinity is low. CTR is a seventransmembrane-domain GPCR that is highly conserved
among vertebrates. It existed before the separation of this
lineage, for it is identified in the invertebrate Ciona intestinalis. RAMP is a single-transmembrane accessory protein that regulates the activities of several GPCRs.
Three types of RAMPs consisting of 148–175 aa residues
exist in mammals, and five types are identified in
teleost fish.
Agonists and Antagonists
Salmon calcitonin. Salmon calcitonin8–32 and AMY8–37.
Biological functions
AMY reduces blood glucose levels. AMY is reported to
suppress glucagon release from pancreatic β cells and is
therefore considered to play a role in glucose homeostasis. There have been contradictory reports regarding the
in vitro effects of AMY on insulin secretion. AMY may
have dual effects on insulin release, which stimulates
basal insulin secretion and suppresses it when insulin
secretion is augmented. A number of studies have been
carried out on the autocrine/paracrine functions of pancreatic AMY, but the mechanisms are still largely
unknown. AMY is believed to inhibit food intake and
gastric emptying in relation to satiety center stimulation.
AMY has also been reported to inhibit insulin-stimulated
glucose uptake and the synthesis of glycogen in isolated
rat skeletal muscle.
Clinical implications
AMY aggregation forms the islet amyloid in the β cells
found in type 2 diabetes. Aggregation occurs in a stepwise manner, with soluble monomeric AMY forming
oligomeric structures, protofibrils, and eventually amyloid fibrils, which are toxic and lead to the cell death of
pancreatic β cells. The proposed mechanisms of AMY induced toxicity during amyloid formation start with cell
membrane disruption; then endoplasmic reticulum stress
causes unfolded protein release and mitochondrial dysfunction, which eventually leads to oxidative stress and
apoptosis. The human AMY20–29 sequence is considered
to determine its ability to form amyloid fibrils. This is
because AMY in other species such as rodents, which
have variations within this region, does not form islet
amyloids. AMY is cosecreted with insulin, and thus is
not produced in type 1 diabetes.
Description
Amylin is a 37-peptide that is structurally similar to CT. Amylin works together with insulin to
regulate glucose concentrations after a meal. When in solution, amylin is viscous, unstable, and
tends to aggregate; therefore it cannot be used parenterally and is not commercially available.
Uses
Amylin functions as part of theendocrinepancreasand contributes toglycemic control. It functions as a synergistic partner to insulin. The overall effect is to slow the rate of appearance (Ra) of glucose in the blood after eating.
Biochem/physiol Actions
Islet amyloid polypeptide (IAPP) is a hormone coexpressed with insulin by pancreatic β-cells. IAPP is used to study the mechanisms of amyloid deposition and its role in molecular misfolding processes expecially in conditions such as diabetes type II.
Clinical Use
Pramlintide, whose sequence is based on rat AMY to
avoid amyloid formation, is used for the treatment of
type 1 and type 2 diabetes to reduce blood glucose levels.
Clinical Use
Amylin normally is cosecreted with insulin from secretory granules in pancreatic β cells in response to meals and works with
insulin to provide postprandial glucose control. Native amylin is a single-chain peptide of 37 amino acids. Observed
deficiencies of amylin in both type 1 and type 2 patients treated with insulin have led to research and drug development
related to amylin.
Structure and conformation
Human AMY is derived after a 67-aa residue proAMY. The short C- and N-terminal flanking peptides are cleaved by the prohormone convertases PC2 and PC1/3 to form the 37-aa residues of mature AMY. Human AMY20–29 is considered to be the responsive region that forms the amyloid fibrils in type 2 diabetes, as synthesized 20–29 aa residues are extremely fibrillogenic. However, rat and mouse models of diabetes lack the islet amyloid. The AMY20–29 regions vary among humans and rodents, and rat/mouse AMY has three proline residues, known as β-sheet breakers, in this region. Because the amyloid is the aggregated protein in which molecules in a β-sheet structure are bound to each other, the lack of the islet amyloid in rodents appears to be due to the presence of proline residues in the AMY20–29 region. Therefore, the peptides in these species are saved from fibrillogenic conformation. The sequence of mature AMY is highly conserved across vertebrate lineages, but the sequence at the position 20–29 regions is variable, which also supports the theory that the islet amyloid is observed only in humans and cats.
Description
DAP Human Recombinant produced in E.Coli is a single, non-glycosylated polypeptide chain containing 125 amino acids (1-102 a.a.) and having a molecular mass of 13.6kDa.
DAP is fused to a 23 amino acid His-tag at N-terminus & purified by proprietary chromatographic techniques.
Background
Death-Associated Protein (DAP) is a proline-rich protein. DAP, which is a negative regulator of autophagy, takes part in the mediation of IFN-gamma-induced cell death.
