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
