Stress-induced recrystallization of a protein crystal by electron irradiation

Ordering of a system of particles into its thermodynamically stable state u sually proceeds by thermally activated mass transport of its constituents. Particularly at low temperature, the activation barrier often hinders equil ibration-this is what prevents a glass from crystallizing(1) and a pile of sand from flattening under gravity. But if the driving force for mass trans port (that is, the excess energy of the system) is increased, the activatio n barrier can be overcome and structural changes are initiated(2). Here we report the reordering of radiation-damaged protein crystals under condition s where transport is initiated by stress rather than by thermal activation, After accumulating a certain density of radiation-induced defects during o bservation by transmission electron microscopy, the distorted crystal recry stallizes, The reordering is induced by stress caused by the defects at tem peratures that are low enough to suppress diffusive mass transport. We prop ose that this defect-induced reordering might be a general phenomenon.