The protofilament structure of insulin amyloid fibrils.
Under solution conditions where the native state is destabilized, the largely helical polypeptide hormone insulin readily aggregates to form amyloid fibrils with a characteristic cross-beta structure. However, there is a lack of information relating the 4.8 A beta-strand repeat to the higher order assembly of amyloid fibrils. We have used cryo-electron microscopy (EM), combining single particle analysis and helical reconstruction, to characterize these fibrils and to study the three-dimensional (3D) arrangement of their component protofilaments. Low-resolution 3D structures of fibrils containing 2, 4, and 6 protofilaments reveal a characteristic, compact shape of the insulin protofilament. Considerations of protofilament packing indicate that the cross-beta ribbon is composed of relatively flat beta-sheets rather than being the highly twisted, beta-coil structure previously suggested by analysis of globular protein folds. Comparison of the various fibril structures suggests that very small, local changes in beta-sheet twist are important in establishing the long-range coiling of the protofilaments into fibrils of diverse morphology.
Jiménez
José L
JL
Department of Crystallography, Birkbeck College, Malet Street, London WC1E 7HX, United Kingdom.
Nettleton
Ewan J
EJ
Bouchard
Mario
M
Robinson
Carol V
CV
Dobson
Christopher M
CM
Saibil
Helen R
HR
D000682:Amyloid / Q000737:chemistry*; D000818:Animals; D002417:Cattle; D020285:Cryoelectron Microscopy; D007091:Image Processing, Computer-Assisted; D066298:In Vitro Techniques; D007328:Insulin / Q000737:chemistry*; D046911:Macromolecular Substances; D008958:Models, Molecular; D017433:Protein Structure, Secondary
D000682:Amyloid; D007328:Insulin; D046911:Macromolecular Substances