Investigation on the Aggregation Behaviors and Filament Morphology of Tau Protein by a Simple 90° Angle Light-Scattering Assay

The in vitro aggregation of tau constructs was monitored by a simple 90° angle light-scattering (LS) approach which was conducted directly on fluorescence instrument. At the optimum incident wavelength (550 nm, unpolarized), the sensitivity of LS was high enough to detect tau aggregation at micromolar range. The nucleation and elongation, different events in the aggregation process of 4RMBD construct (corresponding with the four repeated units of tau Microtubule Binding Domain) could be observed by this approach, as compared with ThS fluorescence assay. The validity of this technique was demonstrated over a range of tau concentrations with different tau filaments. Linear regression of scattering light against concentration yielded the x-intercept, the critical concentrations of tau constructs. The critical concentrations of 4RMBD and its S305N mutant are 5.26 μM and 4.04 μM respectively, indicating point mutation S305N, which is associated with FTDP-17, appear to enhance the heparin-induced tau aggregation in vitro. Furthermore, the slopes of concentration dependence curves, as well as the angle dependence, were discussed based on the filaments morphology examined by electron microscopy and ultrasonication experiment.