| X-RAY DIFFRACTION |
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277 |
Native crystals of GTA/GTB lacking any heavy metals were grown at 4 degrees Celsius from much higher concentrations of protein (30-40 mg/mL for GTB and 16-20 mg/mL for GTA) along with 1% PEG 4000, 4.5-5% 2-methyl-2,4-pentanediol (MPD), 100 mM ammonium sulfate, 70 mM sodium chloride, 50 mM ADA buffer pH 7.5, 30 mM sodium acetate buffer pH 4.6 and 5 mM MnCl2 for GTB crystallization and 5-8 mM CoCl2 for GTA crystallization. 10-15 microlitre drops were placed against a reservoir containing 3.7% PEG 4000, 7% MPD, 0.3 M ammonium sulfate, 0.25 M sodium chloride, 0.2 M ADA buffer and 0.1 M sodium acetate. The crystals were usually grown for 5-10 days. Before making complexes, crystals of GTA/GTB were washed with modified mother liquor ML-2 consisting of 3.5% PEG 4000, 50 mM ammonium sulfate, 40 mM sodium chloride, 35 mM ADA buffer and 15% MPD or glycerol. Crystals of native GTA/GTB in complex with the respective A or B trisaccharide were obtained by soaking them in mother liquor ML-2 with 15% glycerol or MPD and 45-50 mM of each substrate for 2-5 days at 4 degrees Celsius. Before freezing the crystals for data collection, the concentration of the cryoprotectant was made 30% glycerol or 20% MPD respectively |
