Thank you everyone for your ideas. I have shown my diffraction images to a few different people and they think there is some pathology with my crystals - possibly with a very long cell axis in one direction - so I will be testing some more and hopefully finding one that works better, and sending some on a synchrotron trip.
I think I will also sacrifice a crystal or two to dissolve and check that I have crystallised the protein I'm working with.
Cheers,
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
fx: +64 9 3737414
On 18/05/2011, at 11:23 AM, Jim Pflugrath wrote:
> In general, the Rmerge and Rmeas should get better with a lower symmetry
> spacegroup, so that's weird.
>
> Maybe you didn't crystallize what you thought you crystallized. Do people
> runs gels anymore on crystals to get an idea of what's in the crystal or do
> they do MassSpec?
>
> I think another way to go at this is to make images available and have folks
> try to process your data for you. That's starting to become more common
> nowadays.
>
> Jim
>
> -----Original Message-----
> From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of Jason
> Busby
> Sent: Tuesday, May 17, 2011 4:44 PM
> To: [log in to unmask]
> Subject: [ccp4bb] Difficulty indexing diffraction, cell too small
>
> 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
> fx: +64 9 3737414
>
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