On the importance of being amidated: analysis of the role of the conserved C-terminal amide of amylin in amyloid formation and cytotoxicity

Yang, T. and Filippov, I. and Manathunga, L. and Baghai, A. and Marechal, Amandine and Raleigh, D.P. and Zhyvoloup, A. (2024) On the importance of being amidated: analysis of the role of the conserved C-terminal amide of amylin in amyloid formation and cytotoxicity. Biophysical Chemistry 307 (107168), ISSN 0301-4622.

Abstract

The polypeptide hormone Amylin (also known as islet amyloid polypeptide) plays a role in regulation of glucose metabolism, but forms pancreatic islet amyloid deposits in type 2 diabetes. The process of islet amyloid formation contributes to β-cell dysfunction and the development of the disease. Amylin is produced as a pro-from and undergoes processing prior to secretion. The mature hormone contains an amidated C-terminus. Analysis of an alignment of vertebrate amylin sequences reveals that the processing signal for amidation is strictly conserved. Furthermore, the enzyme responsible for C-terminal amidation is found in all of these organisms. Comparison of the physiologically relevant amidated form to a variant with a free C-terminus (Amylin-COO-) shows that replacement of the C-terminal amide with a carboxylate slows, but does not prevent amyloid formation. Pre-fibrillar species produced by both variants are toxic to cultured β-cells, although hAmylin-COO- is moderately less so. Amyloid fibrils produced by either peptide are not toxic. Prior work (ACS Pharmacol. Translational. Sci. 1, 132–49 (2018)) shows that Amylin- COO- exhibits a 58-fold reduction in activation of the Amylin1 receptor and 20-fold reduction in activation of the Amylin3 receptor. Thus, hAmylin-COO- exhibits significant toxicity, but significantly reduced activity and offers a reagent for studies which aim to decouple hAmylin’s toxic effects from its activity. The different behaviours of free and c-terminal amidated Amylin should be considered when designing systems to produce the polypeptide recombinantly.

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