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 <[email protected]> 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:[email protected]] On Behalf Of > RHYS GRINTER > Sent: Tuesday, December 16, 2014 10:37 AM > To: [email protected] > 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 [[email protected]] On Behalf Of Eleanor > Dodson [[email protected]] > Sent: 16 December 2014 15:13 > To: [email protected] > 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 <[email protected]<mailto: > [email protected]>> 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 >
