Analysis of amylin cleavage products provides new insights into the amyloidogenic region of human amylin

Human amylin is the primary component of amyloid deposits found in the pancreatic β-cells of patients with type 2 diabetes mellitus. Recently, two fragments of amylin have been identified in vivo. One fragment contains residues 17 to 37 of human amyline (AMYLIN_17-37) and the other contains residues 24 to 37 (AMYLIN_24-37). The secondary structure and amyloid forming ability of each peptide was determined at pH 5.5(± 0.3) and pH 7.4(± 0.3). Results at these two values of pH were very similar. Both peptides are predominantly unstructured in solution (CD) but adopt a significant amount of β-sheet secondary structure upon aggregation (FTIR). Transmission electron microscopy (TEM) confirmed the presence of amyloid fibrils. AMYLIN_24-37 was further dissected by studying peptides corresponding to residues 24 to 29 and 30 to 37. The AMYLIN_30-37 peptide forms amyloid deposits. Samples of the 24 to 29 fragment which had TFA as the associated counterion formed ordered deposits but samples associated with HCl did not. Residues 20 to 29 are traditionally thought to be the amyloidogenic region of amylin, but this study demonstrates that peptides derived from other regions of amylin are capable of forming amyloid, and hence indicates that these regions of amylin can play a role in amyloid formation.