| 1.C.49 The Cytotoxic Amylin (Amylin) Family The islet amyloid polypeptide (IAPP) precursor (amylin) of mammals is secreted and processed to form channel-forming peptides. These precursor proteins are homologous to calcitonin precursors. The human amylin forms channels in lipid bilayers that are permeable to Na+ , K+, Ca2+ and Cl- (Kourie and Shorthouse, 2000).
Islet amyloid polypeptide (IAPP) and insulin are copackaged and cosecreted by pancreatic islet β-cells. Non-insulin-dependent (type II) diabetes mellitus (NIDDM) is characterized by dysfunction and depletion of these β-cells. An aggregated but not necessarily fibrillar form of IAPP is toxic in cell culture, suggesting that prefibrillar oligomeric (protofibrillar) IAPP may be pathogenic. IAPP generates oligomeric species in vitro that are consumed as β-sheet-rich fibrils grow (Anguiano et al., 2002). Protofibrillar IAPP, like protofibrillar α-synuclein, which is implicated in Parkinson's disease pathogenesis, permeabilizes synthetic vesicles by a pore-like mechanism. The formation of the IAPP amyloid pore is temporally correlated to the formation of early IAPP oligomers, and its disappearance correlates to the appearance of amyloid fibrils. Neither pores nor oligomers are formed by the nonfibrillogenic rat IAPP variant. The IAPP amyloid pore may be critical to the pathogenic mechanism of NIDDM as other amyloid pores may be to Alzheimer's disease and Parkinson's disease. The transport reaction catalyzed by amylin is: ions (in)  ions (out).
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| References: |
Anguiano, M., R.J. Nowak, and P.T. Lansbury, Jr. (2002). Protofibrillar islet amyloid polypeptide permeabilizes synthetic vesicles by a pore-like mechanism that may be relevant to Type II diabetes. Biochemistry 41: 11338-11343.
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Burns, D.M., L. Stehno-Bittel, and T. Kawase. (2004). Calcitonin gene-related peptide elevates calcium and polarizes membrane potential in MG-63 cells by both cAMP-independent and -dependent mechanisms. Am. J. Physiol. Cell Physiol. 287: C457-467.
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Kitamura, K., K. Kangawa, M. Kawamoto, Y. Ichiki, H. Matsuo, and T. Eto. (1992). Isolation and characterization of peptides which act on rat platelets, from a pheochromocytoma. Biochem. Biophys. Res. Commun. 185: 134-141.
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Kourie, J.I. and A.A. Shorthouse. (2000). Properties of cytotoxic peptide-formed ion channels. Am. J. Physiol. Cell Physiol. 278: C1063-C1087.
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| Examples: |
| TC# | Name | Organismal Type | Example |
| 1.C.49.1.1 | Islet amyloid percursor, amylin | Animals | Amylin of Canis familiaris |
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| 1.C.49.1.2 | Calcitonin gene regulatory peptide I precursor, CGRPI of 128 aas and 1 - 3 TMSs. CGRP induces vasodilation, dilating a variety of
vessels including the coronary, cerebral and systemic vasculature. Its
abundance in the CNS points toward a neurotransmitter or
neuromodulator role (Kitamura et al. 1992). It also elevates platelet cAMP and elevates calcium while polarizing the membrane potential by both cAMP-independent and -dependent mechanisms (Burns et al. 2004).
| Animals | CGRPI of Homo sapiens |
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| Examples: |
| TC# | Name | Organismal Type | Example |