| X-RAY DIFFRACTION |
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291 |
Protein was dialyzed in a buffer of 10 mM Tris-HCl, pH 8.5, 1 mM DTT,
concentrated to 4 mg/mL, and inhibitor Ac-DEVD-CHO was added at a 5:1
(w/w) inhibitor/protein ratio. Crystals were obtained at 18 C by the
hanging drop vapor diffusion method using a 4 uL drop that contained
equal amounts of protein and reservoir solution. Each well contained
a reservoir solution (500 uL) of 100 mM sodium citrate, pH 5.4, 23%
PEG 6000, 10 mM DTT, and 3 mM NaN3. Flat, sheet-like crystals appeared
within 14 days, and we used microseeding to obtain diffraction-quality
crystals. In this case, crystal trays were set up as described above and
incubated for 24 hours. The flat sheet crystals were collected and
treated with seed beads using a kit from Hampton Research. A
4 uL drop containing flat sheet crystals was added to a tube containing
seed beads. Reservoir solution
(10 uL) was pipetted on the cover slide to remove all crystals from the
coverslip, and the procedure was repeated five times. The resulting mixture
of crystals and seed beads was vortexed for 30 seconds and cooled on ice for
10 seconds, and the procedure was repeated six times. Serial dilutions of the
treated crystals were set up from 10-1 to 10-3, and 0.5 uL of the 10-2 dilution
crystal seeds was added into the drops of the 24-hour crystal tray. Larger
cube-shaped crystals appeared within 14 days. The crystals were collected and
frozen in liquid nitrogen following the addition of 20% MPD plus the reservoir
solution. |
