Hmmm - well the I212121 cell and the P21221 cells you give here have different volumes, so they cant be just rearrangements of symmetry operators and non-cryst translation.
Do you get other sets of cell dimensions for different processing? Eleanor On 13 October 2014 09:47, Florian Schmitzberger < [email protected]> wrote: > Hi everybody, > > I collected a number of X-ray data sets from crystals originating from the > same cryst. drop. I solved the initial structure in P22121 space group by > MR with Phaser locating two molecules (data to ~ 2.1 Angstr.); refined > R/Rfree: 0.213/0.244. > > Processing of some of the other data sets with XDS/Aimless is consistent > with I222 space group (resolution ~ 2.6 Ang.). I can locate one molecule. > The unit-cell dimensions for I222 and the initial P22121 space groups for > two of the data sets are: > I222: a=87.8 b=101.18 c=123.63; P22121: a=93.34 b=105.47 c=122.98; > > I superposed the molecule in I222 onto one of the two located for the > initially solved P22121; the orientation of the NCS-related molecule in > P22121 differs from the crystallographic-symmetry related one in I222. > Trying to solve this P22121 data set in I222 with MR, does not result in > high Z scores, and maps do not look good. > > Some of the data sets that process in I222 to ~ 3 Angstr., I can also > solve in P22121, locating two molecules (differences may not be that clear > in this case, since the resolution is lower). > > Some other data sets process in P22121 with Aimless; with a substantial > off-origin Patterson peak, indicating translational NCS. For these, Phaser > positions two molecules that are related by crystallographic translational > NCS. These two molecules are crystallographic-symmetry related in the > original P22121 data set. I can also solve these data sets in I222 space > group, with the overall Z score higher than for the P22121 data. > > I am uncertain, what the ‘true’ space group for some of my data sets is. > Could it be that for data that process in P22121, but can be solved in > I222, reflections that would indicate I222 space group were not collected? > Alternatively, perhaps what I am seeing is that there is a (gradual) > transition of the crystal lattice (between P22121 and I222 or vice versa), > caused by variation in crystal handling/cooling or exposure to X-rays. > > It’s relevant to me, because in P22121 space group, a region of the > molecule that is of biological interest makes NCS-related crystal contacts > that are crystallographic-symmetry related in I222. > > Has anybody observed similar cases? I would appreciate comments. > > Cheers, > > Florian > > >
