The formation of spherulites by amyloid fibrils of bovine insulin.
Bovine insulin has long been known to self-assemble in vitro into amyloid fibrils. We have observed a further higher-order self-association of the protein into spherical structures, with diameters typically around 50 microm but ranging from 10 to 150 microm. In a polarizing light microscope, these structures exhibit a "Maltese-cross" extinction pattern typical of spherulites. Spherical structures of a similar size distribution can be observed in the environmental scanning electron microscope, which also reveals the presence of significant amounts of water in the structures. The spherulites contain a large quantity of well defined amyloid fibrils, suggesting that they are formed at least in part as a consequence of the self-assembly of preformed fibrils. Similar structures also have been observed in the tissues of patients suffering from amyloid disorders. The ability of amyloid fibrils to form such higher-order assemblies supports the hypothesis that they represent a generic form of polypeptide structure with properties that are analogous to those of classical synthetic polymers.
Krebs
Mark R H
MR
Department of Physics, Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE, United Kingdom. mrhk2@cam.ac.uk
Macphee
Cait E
CE
Miller
Aline F
AF
Dunlop
Iain E
IE
Dobson
Christopher M
CM
Donald
Athene M
AM
D000682:Amyloid / Q000737:chemistry* / Q000648:ultrastructure*; D000818:Animals; D002417:Cattle; D066298:In Vitro Techniques; D007328:Insulin / Q000737:chemistry*; D046911:Macromolecular Substances; D008854:Microscopy, Electron; D008855:Microscopy, Electron, Scanning; D008958:Models, Molecular; D010316:Particle Size; D017550:Spectroscopy, Fourier Transform Infrared
D000682:Amyloid; D007328:Insulin; D046911:Macromolecular Substances