Three-Dimensional Picometer-Scale Motions in Aqueous Solution Visualized by Diffracted Electron Tracking

Abstract

Diffracted X-Ray tracking (DXT) method has been developed for obtaining dynamical information at single protein molecule level. The motion of an individual single gold nanocrystal can be observed by this method, which is linked to specific site in the molecule, using a time resolved Laue diffraction technique. This method needs a very strong X-ray source, so we continue to develop a compact instrument with use of the electron beam instead of the X-ray. The Electron Back-Scattered Diffraction (EBSD) is adopted to monitor the Three-dimensional (3D) crystal orientation of the gold nanocrystal. We call this the Diffracted Electron Tracking (DET). For this purpose, we have developed the wet cell using the very thin carbon sealing film for maintained atmospheric pressure from high vacuum surroundings of a scanning electron microscope (SEM), and confirmed that the EBSD pattern (EBSP) can be obtained from the gold nanocrystals through the carbon sealing film of the wet cell. When the gold nanocrystal moved by the motion of labeled molecules, the change of the EBSP is observed. Moreover, we confirmed EBSP can be obtained from 40nm diameter of commercial colloidal gold instead of gold nanocrystal. The colloidal gold was more sensitive and more accurate to detect the motion of linked molecule by reason of its good sphericity and well-regulated particle size. Recently, we developed new configuration of the wet cell that might be able to obtain EBSP without intensive electron damages. This method may contribute to develop as a single molecular technology for fragile molecules by electron irradiation. using this method, we are planning to detect rotational motion of the chaperonin protein in the presence of ATP.