Analysis of the Ability of Pramlintide To Inhibit Amyloid Formation by Human Islet Amyloid Polypeptide Reveals a Balance between Optimal Recognition and Reduced Amyloidogenicity

The hormone human islet amyloid polypeptide (hIAPP or amylin) plays a role in glucose metabolism, but forms amyloid in the pancreas in type 2 diabetes (T2D) and is associated with beta-cell death and dysfunction in the disease. Inhibitors of islet amyloid have therapeutic potential; however, there are no clinically approved inhibitors, and the mode of action of existing inhibitors is not well understood. Rat TAPP (rIAPP) differs from hIAPP at six positions, does not form amyloid, and is an inhibitor of amyloid formation by hIAPP. Five of the six differences are located within the segment of residues 20-29, and three of them are Pro residues, which are well-known disruptors of beta-sheet structure. rIAPP is thus a natural example of a beta-breaker inhibitor, a molecule that combines a recognition element with an entity that inhibits beta-sheet formation. Pramlintide (PM) is a peptide drug approved for use as an adjunct to insulin therapy for treatment of diabetes. PM was developed by introducing the three Pro substitutions found in rIAPP into hIAPP. Thus, it more closely resembles the human peptide than does rIAPP. Here we examine and compare the ability of rIAPP, PM, and a set of designed analogues of hIAPP to inhibit amyloid formation by hIAPP, to elucidate the factors that lead to effective peptide-based inhibitors. Our results reveal, for this class of molecules, a balance between the reduced amyloidogenicity of the inhibitory sequence on one hand and its ability to recognize hIAPP on the other.