Identification of a penta- and hexapeptide of islet amyloid polypeptide (IAPP) with amyloidogenic and cytotoxic properties

Pancreatic amyloid is found in more than 95% of type II diabetes patients. Pancreatic amyloid is formed by the aggregation of islet amyloid polypeptid e (hIAPP or amylin), which is a 37-residue peptide. Because pancreatic amyl oid is cytotoxic, it is believed that its formation is directly associated with the development of the disease. We recently showed that hIAPP amyloid formation follows the nucleation-dependent polymerization mechanism and pro ceeds via a conformational transition of soluble hIAPP into aggregated beta -sheets. Here, we report that the penta- and hexapeptide sequences, hIAPP(2 3-27) (FGAIL) and NAPP(22-27) (NFGAIL) of hIAPP are sufficient for the form ation of beta-sheet-containing amyloid fibrils. Although these two peptides differ by only one amino acid residue, they aggregate into completely diff erent fibrillar assemblies, hIAPP(23-27) (FGAIL) fibrils self-assemble late rally into unusually broad ribbons, whereas hIAPP(22-27) (NFGAIL) fibrils c oil around each other in a typical amyloid fibril morphology. hIAPP(20-27) (SNNFGAIL) also aggregates into beta-sheet-containing fibrils, whereas no a myloidogenicity is found for hIAPP(24-27) (GAIL), indicating that hIAPP(23- 27) (FGAIL) is the shortest fibrillogenic sequence of hIAPP. Insoluble amyl oid formation by the partial hIAPP sequences followed kinetics that were co nsistent with a nucleation-dependent polymerization mechanism. hIAPP(22-27) (NFGAIL), hIAPP(20-27) (SNNFGAIL), and also the known fibrillogenic sequen ce, hIAPP(20-29) (SNNFGAILSS) exhibited significantly lower kinetic and the rmodynamic solubilities than the pentapeptide hIAPP(23-27) (FGAIL). Fibrils formed by all short peptide sequences and also by hIAPP(20-29) were cytoto xic towards the pancreatic cell line RIN5fm, whereas no cytotoxicity was ob served for the soluble form of the peptides, a notion that is consistent wi th hIAPP cytotoxicity. Our results suggest that a penta- and hexapeptide se quence of an appropriate amino acid composition can be sufficient for beta- sheet and amyloid fibril formation and cytotoxicity and may assist in the r ational design of inhibitors of pancreatic amyloid formation or other amylo idosis-related diseases. (C) 2000 Academic Press.