[ccp4bb] Question about strange MR solution

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From: Marius Schmidt marius {- dot -} schmidt {- at -} PH {- dot -} TUM {- dot -} DE
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Subject: Re: Question about strange MR solution
From: Marius Schmidt marius {- dot -} schmidt {- at -} PH {- dot -} TUM {- dot -} DE
Date: 2008-02-04

Subject: Question about strange MR solution
From: Michele Lunelli efunit {- at -} YAHOO {- dot -} IT
Date: 2008-02-04

Dear all,

I refined a protein structure in the space group P6(1)22, with one copy in the
asymmetric unit, resolution ~1.8 A, Rwork=0.20, Rfree=0.22.
Then I tried to feed Phaser (version 1.3.3) with this structure. It found
quickly a very prominent solution, but the first euler angle is 180 instead of 0
degrees (the others are 0, as well as the fractional coordinates). This solution
is not symmetry-related with the structure that I used as search model: indeed,
there are a lot of clashes. However, when I refine this solution, I obtain
immediately R factors as good as the search model, and also the electron density
map looks perfect. Of course, I used the same reflections file to refine the
initial structure and the MR solution rotated of 180 degrees.

How can I explain this? The analysis with Truncate (moments and cumulative
intensity distribution) don't suggest any twinning, as well as the
Padilla-Yeates test. Is it possible, that I refined the structure in the wrong
space group?

Thank you in advance,

Michele Lunelli

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CCP4bb <-- 2008 <-- February 2008 <-- 04 February 2008

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From: Marius Schmidt marius {- dot -} schmidt {- at -} PH {- dot -} TUM {- dot -} DE
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Subject: Re: Question about strange MR solution
From: Marius Schmidt marius {- dot -} schmidt {- at -} PH {- dot -} TUM {- dot -} DE
Date: 2008-02-04