In vivo measurement of internal and global macromolecular motions in E. coli

We present direct quasielastic neutron scattering measurements, in vivo, of macromolecular dynamics in E. coli. The experiments were performed on a wide range of time-scales, to cover the large panel of internal and self-diffusion motions. Three major internal processes were extracted at physiological temperature: a fast picosecond (ps) process that corresponded to restricted jump diffusion motions, and two slower processes that resulted from reorientational motions occurring in about 40 ps and 90 ps, respectively. The analysis of the fast process revealed that the cellular environment leads to an appreciable increase in internal molecular flexibility and diffusive motion rates compared to those evaluated in fully hydrated powders. The result showed that the amount of cell water plays a decisive role in internal molecular dynamics. Macromolecular interactions and confinement, however, attenuate slightly the lubricating effect of water, as revealed by the decrease of the in vivo parameters compared to those measured in solution. The study demonstrated that standard sample preparations do not mimic accurately the physiological environment, and suggested that intracellular complexity participates in functional dynamics necessary to biological activity. Furthermore, the method allowed the extraction of the self-diffusion of E. coli macromolecules, which presented similar parameters as those extracted for hemoglobin in red blood cells.