Alpha Synuclein's Anomalous Structural Fluctuations in X-ray Single Molecule Observations

Abstract

The structures of alpha-synuclein (α-syn) in solutions resemble that of a random coil because α-syn is one of the intrinsically disordered protein (IDP). Alpha-syn is of great interest to Parkinson's researchers because it is a major constituent of Lewy bodies. Here, we observed characteristic of structural fluctuation of wild type (WT), phosphorylated mimic (S129E) and familial mutants (A53T, E46K) by using Diffracted X-ray Tracking (DXT) as x-ray single molecule detection systems. DXT is a method of measuring internal motions of the proteins by using trajectories of labeled gold nanocrystal. In order to measure movements of the specific binding sites of proteins, DXT monitors of X-ray diffraction spots from gold nanocrystal that were labeled in the active sites of the proteins. We measured structural fluctuations of individualα-syn molecules with both high time-resolution (36ms/frame and 0.1ms/frame) and high precision (0.1nm scale). DXT experiments used the energy of quasi-white x-rays (energy peak-width of 2%, 10-20 keV, BL40XU, SPring-8). As a result, we discovered that WT's fluctuation is lower than those of other mutants (S129E, A53T and E46K) from observed dynamical motion's histograms. Furthermore, we found that modes of motions in E46K and A53T have closer to that of S129E than that of WT. From motion's histograms in rotatory direction for the chain axis of α-syn's amino acid, we confirmed that motion's histograms in WT has simple single Gaussian distribution. However, those in other mutants have complex ones. From our DXT results, it is very clear that there is specific different motions between WT of α-syn and other mutants. In addition to, we found that there is different number of X-ray diffraction spots from gold nanocrystal between WT of α-syn and other mutants.