The approach used for screening growth conditions is to incubate, under paraffin oil, small aqueous aliquots of the sample protein with chemical mixtures (called ‘cocktails’) that are designed to induce a state of supersaturation. The protein molecules will then be driven out of solution and under proper conditions, crystals will form. In the high-throughput lab, screening experiments are conducted in 1536-well microassay plates using 1536 distinct cocktails containing varying concentrations of salts and other precipitants in buffers spanning a wide pH range.

The high-throughput experiments are set up using Robbins Scientific Tango pipetting robots. Two custom-made, photomicrographic reader tables that can each accommodate as many as 28 crystallization plates are used to document the results with a digital camera. Then, digital images are transferred to a one-terabyte disc storage system, and the plates are stored in temperature-controlled incubators.

The crystallization lab also contains all the equipment needed to optimize crystal size and quality once the initial conditions have been found. The instruments available for preparing and characterizing macromolecular solutions and crystallization cocktails include pH meters, electronic balances, centrifuges, refractometers, a spectrophotometer, a viscometer, and an osmometer. Two DynaPro temperature-controlled dynamic light scattering instruments are available to make measurements of solution homogeneity. These measurements are useful for predicting the likelihood that crystals will form from a solution.

Previous Step: Protein Purification       Next Step: X-ray Diffraction