Designing Conditions for in vitro Formation of Amyloid Protofilaments and Fibrils
Abstract
We have been able to convert a small α /β protein, acylphosphatase, from its soluble and native form into insoluble amyloid fibrils of the type observed in a range of pathological conditions. This was achieved by allowing slow growth in a solution containing moderate concentrations of trifluoroethanol. When analyzed with electron microscopy, the protein aggregate present in the sample after long incubation times consisted of extended, unbranched filaments of 30-50 angstrom in width that assemble subscquently into higher order structures. This fibrillar material possesses extensive β -sheet structure as revealed by far-UV CD and IR spectroscopy. Furthermore, the fibrils exhibit Congo red birefringence, increased fluorescence with thioflavine T and cause a red-shift of the Congo red absorption spectrum. All of these characteristics are typical of amyloid fibrils. The results indicate that formation of amyloid occurs when the native fold of a protein is destabilized under conditions in which noncovalent interactions, and in particular hydrogen bonding, within the polypeptide chain remain favorable. We suggest that amyloid formation is not restricted to a small number of protein sequences but is a property common to many, if not all, natural polypeptide chains under appropriate conditions.
- Publication:
-
Proceedings of the National Academy of Science
- Pub Date:
- March 1999
- DOI:
- 10.1073/pnas.96.7.3590
- Bibcode:
- 1999PNAS...96.3590C