| X-RAY DIFFRACTION |
7.0 |
298 |
HalA crystals were obtained by the hanging drop vapor diffusion method by combining equal volumes of protein solution (HalA (5 mg/ml), lysine (50 mM, pH 7), and aKG (20 mM, pH 7)) and reservoir solution (potassium phosphate monobasic (40 mM), 20% (w/v) PEG 8000, 15% (v/v) glycerol). Crystals grew in three days and were transferred to an Eppendorf tube containing 250 uL of reservoir solution and vortexed for 30 seconds with 10 x 1 uM diameter zirconia/silica beads to produce a micro-seed solution. The seed solution was stored at -80C for future use. Subsequent crystals were prepared by micro-seeding equal volumes of protein solution (HalA (5 mg/ml), lysine (50 mM, pH 7), and aKG (20 mM, pH 7)) and reservoir solution (potassium phosphate monobasic (40 mM), 20% (w/v) PEG 8000, 15% (v/v) glycerol). Crystals grew after two weeks inside a Coy anaerobic chamber. Crystals were soaked with (NH4)2Fe(SO4)2 6H2O (1.42 mM) while NO accumulated in the well. To introduce NO, diethylamine NONOate was prepared by dissolving solid in 10 mM NaOH. The stock concentration was determined based on the published extinction coefficient of e250 = 6,500 M-1 cm-1 using a Nanodrop. NONOate was added to a final concentration of 26 mM in each well along with 150 mM HEPES pH 7.5 to trigger NONOate decomposition. The wells were quickly re-sealed and NO was allowed to accumulate for approximately 1 hour, after which the crystals were flash frozen in liquid nitrogen |
