Amyloid fibril formation from full-length and fragments of amylin.
Amyloiddeposits of fibrillar human amylin (hA) in the pancreas may be a causative 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(8-37) and hA(20-29)-is presented. Circular dichroism spectroscopy revealed that 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) formed flat ribbons consisting of numerous 3. 6-nm-wide protofibrils. In contrast, 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. For full-length hA(1-37), the predominant fibril type contained three protofibrils and for hA(8-37), the predominant type contained two protofibrils. Polymerization 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 demonstrate that the N-terminal region of the hA peptide influences the relative frequencies 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 higher order coiled polymorphic superstructures.
Goldsbury
C
C
Department of Biophysical Chemistry, M. E. Müller Institute for Structural Biology, Basel, Switzerland.
Goldie
K
K
Pellaud
J
J
Seelig
J
J
Frey
P
P
Müller
S A
SA
Kistler
J
J
Cooper
G J
GJ
Aebi
U
U
D000682:Amyloid / Q000378:metabolism* / Q000648:ultrastructure*; D000818:Animals; D001483:Base Sequence; D052160:Benzothiazoles; D002942:Circular Dichroism; D005456:Fluorescent Dyes; D006801:Humans; D058228:Islet Amyloid Polypeptide; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010446:Peptide Fragments; D017433:Protein Structure, Secondary; D051381:Rats; D016415:Sequence Alignment; D013844:Thiazoles
D000682:Amyloid; D052160:Benzothiazoles; D005456:Fluorescent Dyes; D058228:Islet Amyloid Polypeptide; D010446:Peptide Fragments; D013844:Thiazoles; C009462:thioflavin T