Amyloid fibril formation from full-length and fragments of amylin

Amyloid deposits of fibrillar human amylin (hA) in the pancreas may be a ca usative factor in type-2 diabetes. A detailed comparison of in vitro fibril formation by full-length hA(1-37) versus fragments of this peptide--hA(8-3 7) and hA(20-29)-is presented. Circular dichroism spectroscopy revealed tha t fibril formation was accompanied by a conformational change: random coil to beta-sheet/alpha-helical structure. Fibril morphologies were visualized by electron microscopy and displayed a remarkable diversity, hA(20-29) form ed flat ribbons consisting of numerous 3.6-nm-wide protofibrils. In contras t, hA(1-37) and hA(8-37) formed polymorphic higher order fibrils by lateral association and/or coiling together of 5.0-nm-wide protofibril subunits. F or full-length hA(1-37), the predominant fibril type contained three protof ibrils and for hA(8-37), the predominant type contained two protofibrils. P olymerization was also monitored with the thioflavin-T binding assay, which revealed different kinetics of assembly for hA(1-37) and hA(8-37) fibrils. hA(20-29) fibrils did not bind thioflavin-T. Together the results demonstr ate that the N-terminal region of the hA peptide influences the relative fr equencies of the various higher order fibril types and thereby the overall kinetics of fibril formation, Furthermore, while residues 20-29 contribute to the fibrils' beta-sheet core, the flanking C- and N-terminal regions of the hA peptide determine the interactions involved in the formation of high er order coiled polymorphic superstructures. (C) 2000 Academic Press.