That seems hard work to me! Data quality suffers when you discard multiplicity.. Eleanor
On 8 August 2017 at 17:15, Sudipta Bhattacharyya < sudiptabhattacharyya.iit...@gmail.com> wrote: > Hi Giorgio, > > I also suspect the presence of twining and as Eleanor has suggested the L > test is the best test to detect that (if also t-NCS is not present). You > can reprocess your data in P1, do MR in P1 and then feed your P1 model and > mtz file to zanuda to see what SG it suggests. That trick once worked for > me. > > Cheers, > Sudipta. > > > Sudipta Bhattacharyya, > Postdoctoral fellow > Department of Molecular Biosciences > University of Texas at Austin > Texas, USA. > > > On Tue, Aug 8, 2017 at 8:27 AM, Eleanor Dodson <eleanor.dod...@york.ac.uk> > wrote: > >> 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 >>> >> >> >
