Amyloid-like fibril formation in an all beta-barrel protein - Partially structured intermediate state(s) is a precursor for fibril formation

by Srisailam, S.; Kumar, T. K. S.; Rajalingam, D.; Kathir, K. M.; Sheu, H. S.; Jan, F. J.; Chao, P. C.; Yu, C.

Acidic fibroblast growth factor from newt (Notopthalmus viridescens) is a similar to15-kDa, all beta-sheet protein devoid of disulfide bonds. In the present study, we investigate the effects of 2,2,2-trifluoroethanol (TFE) on the structure of newt acidic fibroblast growth factor (nFGF-1). The protein aggregates maximally in 10% (v/v) TFE. Congo red and thioflavin T binding experiments suggest that the aggregates induced by TFE have properties resembling the amyloid fibrils. Transmission electron microscopy and x-ray fiber diffraction data show that the fibrils (induced by TFE) are straight, unbranched, and have a cross-beta structure with an average diameter of 10-15 Angstrom. Preformed fibrils (induced by TFE) of nFGF-1 are observed to seed amyloid-like fibril formation in solutions containing the protein (nFGF-1) in the native beta-barrel conformation. Fluorescence, far-UV CD, anilino-8-napthalene sulfonate binding, multidimensional NMR, and Fourier transformed infrared spectroscopy data reveal that formation of a partially structured intermediate state(s) precedes the onset of the fibrillation process. The native beta-barrel structure of nFGF-1 appears to be disrupted in the partially structured intermediate state(s). The protein in the partially structured intermediate state(s) is found to be "sticky" with a solvent-exposed non-polar surface(s). Amyloid fibril formation appears to occur due to coalescence of the protein in the partially structured intermediate state(s) through solvent-exposed non-polar surfaces and intermolecular beta-sheet formation among the extended, linear beta-strands in the protein.

Journal
Journal of Biological Chemistry
Volume
278
Issue
20
Year
2003
Start Page
17701-17709
URL
https://dx.doi.org/10.1074/jbc.m300336200
ISBN/ISSN
1083-351X; 0021-9258
DOI
10.1074/jbc.m300336200