Hi Carmela, as Jacob suggests, the real space group may be P2 or P2(1). You need to prepare 3 MTZ files, each corresponding to a different unique b axis. So just run XDS 3 times, each time with JOB=CORRECT and SPACE_GROUP_NUMBER=3, and afterwards XDSCONV to create a MTZ file (or pointless/aimless). First time: UNIT_CELL_CONSTANTS= 58 103 220 90 90 90 Second time: UNIT_CELL_CONSTANTS= 103 220 58 90 90 90 Third time: UNIT_CELL_CONSTANTS=220 58 103 90 90 90
Then, if you have a good model, do MR with each MTZ file, taking care that both P2 and P2(1) are tested. Or experimental phasing, but that requires good data. HTH, Kay On Sun, 3 Dec 2017 18:29:57 +0100, Carmela Garcia <c.gar...@bioc.uzh.ch> wrote: >Hi, > >The dimensions for a native are 58 103 220, with small differences for the >derivatives. > >Best, > >Carmela. > >> On 3 Dec 2017, at 18:18, Sridhar Prasad <spra...@calasiapharma.com> wrote: >> >> Hello, >> Can you please share the unit cell dimensions. >> >> Cheers, >> Sridhar >> >> On Dec 3, 2017 9:13 AM, "Carmela Garcia" <c.gar...@bioc.uzh.ch >> <mailto:c.gar...@bioc.uzh.ch>> wrote: >> Dear all, >> >> I know that some years ago a similar situation was discussed here, and I >> wonder if someone has new insights about these problems. >> >> My protein is a dimer in solution. I tried several derivatives for SAD, and >> all my datasets seem to have the same problem, including the native >> crystals. I processed the data with XDS and the space group determination >> was done with Pointless, being a P212121. >> >> Checking the quality of the data, I found several problematic results: >> >> - Translational NCS is detected. There is a peak at (0.50, 0.40, 0.50) >> - The L test suggests twinning (L statistic = 0.41) >> - The mean acentric moments I from input data have the following values: >> <I^2>/<I>^2 : 4.396 >> <I^3>/<I>^3: 34.478 >> <I^4>/<I>^4: 361.084 >> All these values are way higher than the expected ones for non-twinned >> data. >> - The twinning fraction from L-test is 0.22 >> >> This would all suggest that my space group is wrong, and that I should >> proceed in a lower symmetry group, but I don’t know how should I continue. I >> know about cases where a P43212 or a P41212 were suggested but in fact the >> correct space group was P212121, but I would not know how to continue going >> down. Checking my images, I can see some streaky spots, and the crystals >> grow first as needles that eventually become plates and rarely crystals. All >> these would be a clear indicative of twinning, but I would not expect to >> have the same results with different derivatives. We thought about some kind >> of reticular twinning, and I wonder if there is a way to solve it. >> >> Any idea about how to proceed or to identify the problem would be welcome. >> >> Thanks, >> >> Carmela. >> >> >> >> Carmela Garcia-Doval >> University of Zurich >> Department of Biochemistry >> Winterthurerstrasse 190 >> <https://maps.google.com/?q=Winterthurerstrasse+190&entry=gmail&source=g> >> CH-8057 Zurich >> Switzerland >> E-mail: c.gar...@bioc.uzh.ch <mailto:c.gar...@bioc.uzh.ch> > >
