First of all - check whether your crystal data shows twinning - thee is an L-test plot which usually gives a clear indication and if you are using GUI2 the report suggests if this is so.
If you have twinning the most likely SG is P31 (or P32 ) - you cant tell the difference till the structure is solved. Check the merging stats in that point group - Then try MR searches in the two spacegroups. The C2 and I2 SGs are probably sub-group possibilities if you reindex - there are common cell dimensions -pointless output tells you how to do that - but in general one always chooses the highest symmetry that gives reasonable merging statistics and is sensible. Eleanor On 8 August 2017 at 14:15, Giorgio Giardina <giorgio.giard...@uniroma1.it> wrote: > Hello everybody, > > I think I have a pseudo-centering problem. > > I have a 1.6 ang. dataset of a mutant protein that is an homodimer in > solution. > Data processing gives the following SG: > > Space group: P 31 2 1 > Average unit cell: 111.36 111.36 28.56 90.00 90.00 120.00 > Average mosaicity: 0.24 > Rmerge Overall 0.07 > > However with this SG the unit Cell is too small and monomer doesn't fit > the in the AU. > > I reprocessed the data in other possible SG (including P6) and finally I > got 2 equivalent SG's in which I can get a correct Molecular Replacement > solution: > > Space group: I 1 2 1 > Average unit cell: 57.07 111.11 192.90 90.00 90.07 90.00 > > and > > Space group: C 1 2 1 > Average unit cell: 201.10 111.11 57.07 90.00 106.42 90.00 > > Both with Average mosaicity: 0.38 and Rmerge Overall 0.06, > but the corresponding MR solutions do not refine, with R-factor stuck to > 45-47%. > > From what I understand, in the I121 SG I have the NC two-fold axis of the > dimer at 1/2a and this originates the pseudo centering and the small P3 Cell > > Largest Patterson peak with length larger than 15 Angstrom: > Frac. coord. : 0.500 0.000 0.000 > Distance to origin : 28.566 > Height relative to origin : 53.830 % > > I'm really not so good with symmetry, so I'll be grateful for any > suggestion/help/solution from you out there. > Many thanks, > Giorgio >
