There are a couple of tricks I know for dealing with datasets that are
problematic to index (ignore if you've tried them):
1. double-check the machine parameters (detector to crystal distance and
beam center in particular).
2. Index in mosflm using widely separated images (usually n,n+45,n+90)
starting from a strong zone.
3. In really problematic cases, I've sometimes had to resort to manual
spot picking (thankfully not for many years).
Good luck,
Pete
Jason Busby wrote:
Hi,
I have a diffraction data-set from a hexagonal rod shaped crystal, to about 2.0 Å. The problem comes when I try to process the data - Mosflm won't index it, and XDS indexes it as P622, but the unit cell is too small to contain even a single molecule of my protein. I have tried integrating it in some different space groups that XDS suggested (P2, C2, P1) but in all cases the Rmerge and Rmeas are worse than for P622.
If I scale in P622 (or any of the other space groups) I get odd results from
the twinning tests. For example, the 4th moment of E (expected values of 2 for
untwinned, 1.5 for perfect twin) is around 1.1, and the L-test and cumulative
intensity distribution are unusual as well (uploaded images here:
http://tinypic.com/r/65rfr7/7 and here: http://tinypic.com/r/30adgyr/7 )
Has anyone else had similar issues? Any ideas would be appreciated.
Thanks,
Jason.
--
Jason Busby
PhD Student
Laboratory of Structural Biology
School of Biological Sciences
University of Auckland
Thomas Building 110
3a Symonds St
Private Bag 92019
Auckland 1142
New Zealand
ph: +64 9 3737599 ext 83888
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