posted on 2016-02-19, 17:00authored byYuta Suzuki, Jeffrey
R. Brender, Molly T. Soper, Janarthanan Krishnamoorthy, Yunlong Zhou, Brandon T. Ruotolo, Nicholas
A. Kotov, Ayyalusamy Ramamoorthy, E. Neil G. Marsh
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 19F NMR along with other techniques, we are able to show that
multiple oligomeric species can be detected during the lag phase of
Aβ1–40 fiber formation, consistent with a
complex mechanism of aggregation. At least six types of oligomers
can be detected by 19F NMR. These include the reversible
formation of large β-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 ∼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.