Dynamical Observations of Membrane Proteins: The Case of Bacteriorhodopsin.

A new x-ray methodology, Diffracted X-ray Tracking (DXT), has been proven to be a valuable tool in observing intramolecular conformational changes of individual single molecules in real time and space. In order to achieve DXT, the fabrication of dispersive nanocrystals is one of the most important technologies, because DXT system monitors the diffracted x-ray (Laue) spots from nanocrystals labeled with single bio-molecules. In this study, we fabricated one-dimensional gold nanocrystals with an average diameter size of 16 nm using vacuum evaporation. Furthermore, using these nanocrystals, we succeeded in observing normal Brownian motions and momentary structural changes of a single-membrane protein (Bacteriorhodopsin: BR) in a membrane due to the expression of its function. The average movement of the momentarily structural changes in the 35th residue of BR was 76 ± 48 pm, and this agrees with estimated movements from known x-ray crystallography data. This result is an important step toward realizing in-vivo observations of single-molecular conformational changes in membrane proteins. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]