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.