Resolution of Oligomeric Species during the Aggregation of Aβ1-40 Using 19F NMR

In the commonly used nucleation-dependent model of protein aggregation, aggregation proceeds only after a lag phase in which the concentration of energetically unfavorable nuclei reaches a critical value. The formation of oligomeric species prior to aggregation can be difficult to detect by current spectroscopic techniques. By using real-time F-19 NMR along with other techniques, we are able to show that multiple oligomeric species can be detected during the lag phase of A beta(1-40) fiber formation, consistent with a complex mechanism of aggregation. At least six types of oligomers can be detected by F-19 NMR. These include the reversible formation of large beta-sheet oligomer immediately after solubilization at high peptide concentration, a small oligomer that forms transiently during the early stages of the lag phase, and four spectroscopically distinct forms of oligomers with molecular weights between similar to 30 and 100 kDa that appear during the later stages of aggregation. The ability to resolve individual oligomers and track their formation in real-time should prove fruitful in understanding the aggregation of amyloidogenic proteins and in isolating potentially toxic nonamyloid oligomers.