Abstract

There is no guarantee that a given protein has a crystalline phase, but if it does then it has been established that proteins crystallize like all other molecules through a process known as “nucleation and growth”. If a protein can be crystallized then it has optimal equilibrium crystallization conditions; e.g. temperature, protein concentration, pH and precipitant type and concentration. Normally, these conditions are found through extensive screening followed by optimization around hits. Traditionally, minimal attention is paid to the crystallization kinetics, but since nucleation and growth are both non-equilibrium processes, supersaturation kinetics plays an extremely important role in the crystallization process. The optimal crystallization strategy should not only screen equilibrium conditions, but should screen kinetic trajectories through a supersaturation “dimension”.

The most common crystallization methods are vapor phase and microbatch. Each method scans just one kinetic path in which the supersaturation monotonically increases in time. The Crystal Optimizer, in contrast, explores thousands of different kinetic paths in an attempt to find the optimal one in which supersaturation is held high until one crystal nucleates then subsequently is lowered to suppress further nucleation, while still allowing slow growth. One major virtue of our technology is that it is designed to be low tech, easy to use and cheap to produce to facilitate adoption by the structural biology community.