Stress-induced recrystallization of a protein crystal by electron irradiation

Ordering of a system of particles into its thermodynamically stable state usually proceeds by thermally activated mass transport of its constituents. Particularly at low temperature, the activation barrier often hinders equilibration--this is what prevents a glass from crystallizing and a pile of sand from flattening under gravity. But if the driving force for mass transport (that is, the excess energy of the system) is increased, the activation barrier can be overcome and structural changes are initiated. Here we report the reordering of radiation-damaged protein crystals under conditions where transport is initiated by stress rather than by thermal activation. After accumulating a certain density of radiation-induced defects during observation by transmission electron microscopy, the distorted crystal recrystallizes. The reordering is induced by stress caused by the defects at temperatures that are low enough to suppress diffusive mass transport. We propose that this defect-induced reordering might be a general phenomenon.