Identifying the Role of Individual Seal IAPP Amino Acids in Inhibiting the Aggregation of Human IAPP

INTRODUCTION: The progression of type 2 diabetes in humans appears to be linked to the loss of insulin-producing β-cells. One of the major contributors to β-cell loss is the formation of toxic human IAPP amyloid (hIAPP, Islet Amyloid Polypeptide, amylin) in the pancreas. Inhibiting the formation of toxic hIAPP amyloid could slow, if not prevent altogether, the progression of type 2 diabetes. Many non-human organisms also express amyloidogenic IAPP variants known to kill pancreatic cells and give rise to diabetes-like symptoms. Surprisingly, some of these non-human IAPP variants function as inhibitors of hIAPP aggregation, raising the possibility of developing non-human IAPP peptides into anti-diabetic therapeutic peptides. One such inhibitory IAPP variant is seal IAPP, which has been shown to inhibit hIAPP aggregation. Seal IAPP only differs from hIAPP by three amino acids. In this study, each of the six seal/human IAPP permutations was analyzed to identify the role of each of the three amino acid positions in inhibiting hIAPP aggregation. AIMS: This study aimed to identify the minimal amino acid substitutions to yield a peptide inhibitor of human IAPP aggregation. OBJECTIVE: The goal of the study was to determine the minimal amino acid substitutions necessary to convert human IAPP into an amyloid-inhibiting peptide. METHODS: The formation of toxic hIAPP amyloid was monitored using Thioflavin T binding assays, atomic force microscopy, and MTT cell rescue studies. RESULTS: One seal IAPP variant retained amyloid-inhibition activity, and two variants appeared to be more amyloidogenic and toxic than wild-type human IAPP. CONCLUSION: These results suggest that inhibition of hIAPP requires both the H18R and F23L substitutions of hIAPP.