Analysis of Amylin Consensus Sequences Suggests that Human Amylin is Not Optimized to Minimize Amyloid Formation and Provides Clues to Factors that Modulate Amyloidogenicity.

The neuropancreatic polypeptide hormone amylin forms pancreatic islet amyloid in type-2 diabetes. Islet amyloid formation contributes to β-cell death in the disease and to the failure of islet transplants, but the features which influence amylin amyloidogenicity are not understood. We constructed an amino acid sequence alignment of 202 sequences of amylin and used the alignment to design consensus sequences of vertebrate amylins, mammalian amylins, and primate amylins. Amylin is highly conserved, but there are differences between human amylin and each consensus sequence, ranging from one to six substitutions. Biophysical analysis shows that all of the consensus sequences form amyloid, but do so more slowly than human amylin in vitro. The rate of amyloid formation by the primate consensus sequence is 3 to 4-fold slower than human amylin, the mammalian consensus sequence is approximately 20 to 25-fold slower, and the vertebrate consensus sequence approximately 6-fold slower. All of the consensus sequences are moderately less toxic than human amylin towards a cultured β-cell line, with the vertebrate consensus sequence displaying the largest reduction in toxicity of 3 to 4-fold. All of the consensus sequences activate a human amylin receptor and exhibit only modest reductions in activity, ranging from 3 to 4-fold as judged by a cAMP production assay. The analysis argues that there is no strong selective evolutionary pressure to avoid the formation of islet amyloid and provides information relevant to the design of less amyloidogenic amylin variants.