[phenixbb] phaser MR
rjr27 at cam.ac.uk
Fri Jul 24 01:58:23 PDT 2009
If you're unlucky, a combination of pseudo-symmetry and twinning gives
only weak indications of twinning, because the twin-related
reflections are correlated but the twinning tests assume that they are
not. It might be worth considering that possibility. You could try
solving the structure in lower symmetry space groups to see whether
you get a solution that does not exactly obey the higher symmetry.
Are you really certain about the space group? If one symmetry
operator is wrong (e.g. a 2-fold instead of a 2-fold screw), some of
the symmetry operators are still right, and you can get an apparent
solution that partly explains the data. It might be worth running
tests in all the variants of P422 as well.
On 23 Jul 2009, at 22:54, sbiswas2 at ncsu.edu wrote:
> Hi Francis,
> Thanks for your response. The matthews coefficient suggests two
> in the AU. Phaser also finds two molecules. I ran the dataset through
> phenix xtriage it did not indicate twinning though. The molecule also
> exists in nature as a monomer.
>> Twinning? What's your matthews coefficient say? Do you know if your
>> structure is a multimer (biochemistry, etc)? Does it agree with the
>> matthews coefficient?
>> If the unit cell is not big enough to hold all of the contents,then
>> this is an indicator for twinning .
>> On Jul 23, 2009, at 3:09 PM, sbiswas2 at ncsu.edu wrote:
>>> Hi all,
>>> I was trying to solve a structure by molecular replacement. I scaled
>>> data in P4222 space group (resolution 2.7A) with two molecules in
>>> assymmetric unit (molecule A and B) I ran phaser with my model and
>>> got a
>>> Zscore of 5.1. When I look at the map that I got from phaser I could
>>> easily see good electron density for both molecules, However upon
>>> inspection of the electron density map there were considerable
>>> or clashes with molecule B and a symmetry atom. Molecule A had no
>>> however with the symmetry atoms. I was wondering if anyone knows how
>>> resolve this. Could it be a problem of space group. The statistics
>>> good for space group P4222 and the I/sigI was good till 2.7A.
>>> Any advice is appreciated,
>>> phenixbb mailing list
>>> phenixbb at phenix-online.org
>> Francis Reyes M.Sc.
>> 215 UCB
>> University of Colorado at Boulder
>> gpg --keyserver pgp.mit.edu --recv-keys 67BA8D5D
>> 8AE2 F2F4 90F7 9640 28BC 686F 78FD 6669 67BA 8D5D
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Randy J. Read
Department of Haematology, University of Cambridge
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