Aggregation and fibrillation of bovine serum albumin.
The all-alpha helix multi-domain protein bovine serum albumin (BSA) aggregates at elevated temperatures. Here we show that these thermal aggregates have amyloid properties. They bind the fibril-specific dyes Thioflavin T and Congo Red, show elongated although somewhat worm-like morphology and characteristic amyloid X-ray fiber diffraction peaks. Fibrillation occurs over minutes to hours without a lag phase, is independent of seeding and shows only moderate concentration dependence, suggesting intramolecular aggregation nuclei. Nevertheless, multi-exponential increases in dye-binding signal and changes in morphology suggest the existence of different aggregate species. Although beta-sheet content increases from 0 to ca. 40% upon aggregation, the aggregates retain significant amounts of alpha-helix structure, and lack a protease-resistant core. Thus BSA is able to form well-ordered beta-sheet rich aggregates which nevertheless do not possess the same structural rigidity as classical fibrils. The aggregates do not permeabilize synthetic membranes and are not cytotoxic. The ease with which a multidomain all-alpha helix protein can form higher-order beta-sheet structure, while retaining significant amounts of alpha-helix, highlights the universality of the fibrillation mechanism. However, the presence of non-beta-sheet structure may influence the final fibrillar structure and could be a key component in aggregated BSA's lack of cytotoxicity.
Holm
Nikolaj K
NK
Centre for Insoluble Protein Structures (inSPIN) at Department of Life Sciences, Aalborg University, Sohngaardsholmsvej 49, DK-9000 Aalborg, Denmark.
Jespersen
Stine K
SK
Thomassen
Lise V
LV
Wolff
Tine Y
TY
Sehgal
Pankaj
P
Thomsen
Line A
LA
Christiansen
Gunna
G
Andersen
Christian Beyschau
CB
Knudsen
Anders D
AD
Otzen
Daniel E
DE
D000682:Amyloid / Q000648:ultrastructure*; D000818:Animals; D052160:Benzothiazoles; D002417:Cattle; D002470:Cell Survival; D003224:Congo Red / Q000737:chemistry; D009447:Neuroblastoma; D017433:Protein Structure, Secondary; D012710:Serum Albumin, Bovine / Q000737:chemistry* / Q000648:ultrastructure*; D017550:Spectroscopy, Fourier Transform Infrared; D013844:Thiazoles / Q000737:chemistry; D014357:Trypsin / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014961:X-Ray Diffraction
D000682:Amyloid; D052160:Benzothiazoles; D013844:Thiazoles; C009462:thioflavin T; D012710:Serum Albumin, Bovine; D003224:Congo Red; D014357:Trypsin