X-ray observations of single bio-supramolecular photochirogenesis

Structural dynamics of a DNA-binding protein analyzed using diffracted X-ray tracking

Diffracted X-ray tracking (DXT) is one of methods for the real-time evaluation of protein structural dynamics by detecting the movement of a gold-nanocrystal attached to a target protein. However, one of the technical concerns is the size of the gold-nanocrystals, which are larger than the protein. In our previous results of mean square angular displacement curves in DXT analysis, dynamical movements of the DNA-binding protein, c-Myb R2R3, were observed in only one population in either DNA-unbound or -bound state, and was found to decrease upon DNA binding. In this study, c-Myb R2R3 dynamical movements were re-evaluated with a low density of the protein immobilized on the DXT substrate, to decrease the possibility that the gold-nanocrystals attached to more than one R2R3 molecule. We observed two dynamical moving populations in the DNA-bound state, which could be classified due to electrostatic attraction and repulsion between the DNA-protein complexes, and determined the apparent angular diffusion constant, which was similar to the value calculated in our previous study. We showed more real movement of the protein could be observed by lowering the immobilization density of the protein.

Tilting and rotational motions of silver halide crystal with diffracted X-ray blinking

The dynamic properties of crystalline materials are important for understanding their local environment or individual single-grain motions. A new time-resolved observation method is required for use in many fields of investigation. Here, we developed in situ diffracted X-ray blinking to monitor high-resolution diffraction patterns from single-crystal grains with a 50 ms time resolution. The diffraction spots of single grains of silver halides and silver moved in the θ and χ directions during the photolysis chemical reaction. The movements of the spots represent tilting and rotational motions. The time trajectory of the diffraction intensity reflecting those motions was analysed by using single-pixel autocorrelation function (sp-ACF). Single-pixel ACF analysis revealed significant differences in the distributions of the ACF decay constants between silver halides, suggesting that the motions of single grains are different between them. The rotational diffusion coefficients for silver halides were estimated to be accurate at the level of approximately 0.1 to 0.3 pm²/s. Furthermore, newly formed silver grains on silver halides correlated with their ACF decay constants. Our high-resolution atomic scale measurement—sp-ACF analysis of diffraction patterns of individual grains—is useful for evaluating physical properties that are broadly applicable in physics, chemistry, and materials science.