Abstract
One of the current greatest challenges in structural biology is to study protein dynamics over a wide range of time scales in complex environments, such as the cell. Among magnetic resonances suitable for this approach, Electron Paramagnetic Resonance spectroscopy coupled to Site-Directed Spin Labeling (SDSL-EPR) has emerged as a promising tool to study protein local dynamics and conformational ensembles. In this work, we exploit the sensitivity of nitroxide labels in reporting protein local dynamics at room temperature. We demonstrate that such studies can be performed by preserving both the integrity of the cells and the activity of the protein under investigation. Using this approach, we studied the structural dynamics of the chaperone NarJ in its natural host cell, Escherichia coli. We established that spin-labeled NarJ is active inside the cells. We showed that the cellular medium affects NarJ structural dynamics in a sitespecific way, while the structural flexibility of the protein is maintained. Finally, we present and discuss data on the time-resolved dynamics of NarJ in cellular context.