CRYSTAL-GROWTH AND CRYSTAL IMPROVEMENT STRATEGIES

The diffraction resolution of crystals of the guanine nucleotide-excha nge factor complex, EF-Tu-Ts, has been extended from 5.0 to 2.5 angstr om by lowering the solvent content in the, crystals as well as the tem perature of data collection. The common form of EF-Tu-Ts crystal belon gs to space group P2(1)2(1)2(1) with a = 81.1, b 109.9, c = 207.5 angs trom and has a solvent content of 61 The crystals diffract to a resolu tion of 5.0 angstrom at 293 K and 4.0 angstrom at 273 K. When cryoprot ective agents are slowly diffused into the crystals, the cell constant s shrink to a = 74.4, b = 109.9, c = 198.7 angstrom and the solvent co ntent falls to 55%. After the cryoprotective agent has been added, the crystals diffract to 2.7 angstrom resolution at 293 or 273K and 2.5 a ngstrom at 250 K. X-ray diffraction data, collected before and after t he transformation of individual EF-Tu-Ts crystals, demonstrate that a large percentage of the improvement in diffraction resolution is due s olely to the addition of cryoprotective agents. The transfer procedure s for the successful introduction of cryoprotective agents into EF-Tu- Ts crystals as well as the general applicability to other crystal syst ems will be discussed.