FIGURE 3.

Protofibril dissociation. A, normalized fluorescence emission spectra of ZAβ3W after the addition of an Aβ42 protofibril sample and incubation at 25 °C for 10 min or 1, 2, 3, 4, or 5 h. The protein concentrations used were 14.8 μm Aβ42 and 19.6 μm ZAβ3W. Spectra of free ZAβ3W and ZAβ3W bound to a stoichiometric amount of Aβ42 monomers are shown for comparison. B, SEC of an Aβ42 protofibril sample re-injected onto a Superdex 75 10/300 column after incubation for 20 min in the absence of ZAβ3W. In addition to protofibrils eluting at ∼9 ml, Aβ monomers eluting at ∼14.5 ml were detected. AU, absorbance units. C, transmission electron microscopy of fresh Aβ42 protofibrils (upper panel), Aβ42 protofibrils at the end of the dissociation experiment (middle panel), and Aβ42 protofibrils treated as in the dissociation experiment but in the absence of ZAβ3W (lower panel). D, normalized fluorescence emission spectra of ZAβ3W after the addition of an Aβ42 amyloid fibril sample and incubation at 25 °C for 10 min or 2 or 7 days (d). The protein concentrations used were 20 μm Aβ42 and 25 μm ZAβ3W. Spectra of free ZAβ3W and ZAβ3W bound to a stoichiometric amount of Aβ42 monomers are shown for comparison. E, sedimentation coefficient distribution of ZAβ3W (black) and of the Aβ42 protofibril fraction in the presence of ZAβ3W at the end of the dissociation experiment (red). The shift of the distribution maximum to a higher s-value upon addition of protofibrils to ZAβ3W demonstrates formation of the ZAβ3W-Aβ42 complex. The complete distribution is shown in the inset.