I'd rather go for a complete low resolution dataset. Is this a native
crystal ? HA derivative ? Even with a 4Å data set you can do something
it's painful but not impossible e.g. molecular replacement if
possible. Then at least you would know your spacegroup & perhaps gain
some insights from the crystal lattice which you might then modify for
better crystallizability.
I would look at your current dataset and see where the resolution
drops off to e.g. 4.5 Å Add the total exposure time until you reach
that decay and divide this by 90 (images), this will be your safest
bet for an estimated exposure time to get a complete dataset. It might
be in your case 1 second or even less than that, if it's less than 1
second I'd rather increase the oscillation range (assuming you don't
have high mosaicity/overlaps).
Now that you know how long the crystals might survive in the beam, you
should plan your data collection carefully and run Strategy in Mosflm
for an optimal starting point.
If you are trying denovo phasing you should be looking for a 6Å
complete dataset to at least be able to locate the HA sites.
How big are your crystals ? If they're tiny get larger ones they will
diffract better.
Jürgen
On 4 Aug 2008, at 10:30, lei feng wrote:
hello everyone, I am seeking help on a crystal decay problem
I got crystals of a protein , but it decayed very fast in syncrotron
beam. From the initial index, it is P222 space group, I need about
180 images, its initial diffraction went to about 3 A, and after
70-80 images, it droped to about 6. I already used low exposure time
and it is in cryo , what I can do ? any suggestion is appreciated.
BTW. the condition of crystallization is 0.1M NaAC, pH 5.5, 1 M
LiCl, 15% PEG 6000,
I used 5 seconds / image , which can go to 3 A, if I use 2 seconds,
the initial resolution is only 3.5 A ( beam energy 12kev)
Thanks
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Jürgen Bosch
University of Washington
Dept. of Biochemistry, K-426
1705 NE Pacific Street
Seattle, WA 98195
Box 357742
Phone: +1-206-616-4510
FAX: +1-206-685-7002
Web: http://faculty.washington.edu/jbosch
