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:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Jason > Busby > Sent: Tuesday, May 17, 2011 4:44 PM > To: CCP4BB@JISCMAIL.AC.UK > 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 >
