I agree here. The 50 % could be a good indicator. I am finishing a new structure which was about 42% twinned in the monoclinic setting (b = ~90) for an Se-Met dataset. When I went to refine it with the native dataset, the twin fraction increased to 50%, figured something wasn't right. fortunately, the native was much better behaved / untwinned in an orthorhomic crystal form with a near identical unit cell.
-tg ________________________________ From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of Eleanor Dodson [eleanor.dod...@york.ac.uk] Sent: Tuesday, December 16, 2014 2:36 PM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] P31 or P32 But are you sure it is twinned and not really P312? Ltest etc is a pretty reliable indicator but the results can be biased by non-crystallographic translation, etc And do the HA sites obey the twinning symmetry? On 16 December 2014 at 16:36, Keller, Jacob <kell...@janelia.hhmi.org<mailto:kell...@janelia.hhmi.org>> wrote: I would say try to get better crystals and data, and also do a MAD experiment. But...perfect twins are really hard, I think. Maybe vary the crystallization conditions a bit, additive screen, seeding, etc. JPK -----Original Message----- From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK<mailto:CCP4BB@JISCMAIL.AC.UK>] On Behalf Of RHYS GRINTER Sent: Tuesday, December 16, 2014 10:37 AM To: CCP4BB@JISCMAIL.AC.UK<mailto:CCP4BB@JISCMAIL.AC.UK> Subject: Re: [ccp4bb] P31 or P32 Hi Eleanor, The data is perfectly twinned, with the original auto processing assigning a point group of P312, but I reprocessed it in P3 and it seems to be behaving okay. Are there any additional precautions I should take at the phasing stage with twinned data? BW Rhys ________________________________________ From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK<mailto:CCP4BB@JISCMAIL.AC.UK>] On Behalf Of Eleanor Dodson [eleanor.dod...@york.ac.uk<mailto:eleanor.dod...@york.ac.uk>] Sent: 16 December 2014 15:13 To: CCP4BB@JISCMAIL.AC.UK<mailto:CCP4BB@JISCMAIL.AC.UK> Subject: Re: [ccp4bb] P31 or P32 Sorry - of course it can.. Sorry. Only if the twinning is perfect then you apparently get a higher symmetry.. Eleanor On 16 December 2014 at 14:26, Tim Gruene <t...@shelx.uni-ac.gwdg.de<mailto:t...@shelx.uni-ac.gwdg.de><mailto:t...@shelx.uni-ac.gwdg.de<mailto:t...@shelx.uni-ac.gwdg.de>>> wrote: Dear Rhys, I would try to place idealised secondary structure elements with coot into the density - at this resolution they probably fit both hands, but you may see a difference when you do e.g. rigid body refinement. Best, Tim On 12/16/2014 10:39 AM, RHYS GRINTER wrote: > Hi All, > > This will no doubt show something of my ignorance with experimental phasing, > however I'm currently working on solving a 3.8A SAD dataset with Pt anomalous > signal. Both Shelx and Xtriage see reasonable anomalous signal to about 7A > and seem to get statistics suggesting a solution when I run SAD phasing > using Autosol in Phenix. After density modification I get pretty nice looking > maps with clear solvent channels and interconnected density for protein, > however there is very little difference in map R-factor between the hands and > the maps from both the P31 and P32 solution appear comparable in structure. > Obviously DM is struggling to break the hand ambiguity, however can some one > tell me if what I'm seeing represents a definite solution? And what is the > best way to proceed from here? > > Cheers, > > Rhys > -- Dr Tim Gruene Institut fuer anorganische Chemie Tammannstr. 4 D-37077 Goettingen GPG Key ID = A46BEE1A
