Try P2 SG’s. JPK
From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Carmela Garcia Sent: Sunday, December 3, 2017 12:30 PM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] P212121 twinning 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<mailto: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>
