Radiation Damage Limits to XPCS Studies of Protein Dynamics

The limitations to x-ray photon correlation spectroscopy (XPCS) imposed by radiation damage have been evaluated for suspensions of alpha crystallin. We find that the threshold for radiation damage to the measured protein diffusion rate is significantly lower than the threshold for damage to the protein structure. We provide damage thresholds beyond which the measured diffusion coefficients have been modified using both XPCS and dynamic light scattering (DLS).