Could this be as banal as having different origins in the different P1 solutions?
Doesn't explain the poor refinement, though.
JPK
-----Original Message-----
From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of Randy Read
Sent: Monday, September 19, 2016 4:28 PM
To: [log in to unmask]
Subject: Re: [ccp4bb] multiple similar solutions in phaser
Hi,
This is exactly what you’d expect to see with a repetitive structure. One way or another, you have to figure out the sequence registration. Jacob’s suggestion of SAD phases is great if you have any anomalous signal, but at this resolution you might see some good hints about side chain identities in maps phased with, say, a polyAla model. As soon as you can reliably do 4-fold averaging, it should just drop out.
This is also the kind of thing that Arcimboldo is very good at, where the SHELXE density modification step will probably help a great deal.
Presumably you’re confident that it’s really P1 and not really a higher symmetry (as checked, for instance, with pointless or phenix.xtriage)?
Best wishes,
Randy
-----
Randy J. Read
Department of Haematology, University of Cambridge
Cambridge Institute for Medical Research Tel: +44 1223 336500
Wellcome Trust/MRC Building Fax: +44 1223 336827
Hills Road E-mail: [log in to unmask]
Cambridge CB2 0XY, U.K. www-structmed.cimr.cam.ac.uk
> On 19 Sep 2016, at 16:48, Abhishek Jalan <[log in to unmask]> wrote:
>
> Dear all,
>
> I am trying to solve the structure of a collagen triple helix using phaser. The crystal diffracts to 2.0 A in P1 space group. Matthew's coefficient suggests 4 molecules in the asu. When I tried to search for 5 components, phaser gave 8 solutions each containing 4 triple helices. The LLG scores are in the range of 2200 and TFZ around 15.
> All 8 solutions are similar except that the triple helices slide either up or down with respect to each other in different solutions.
>
> Refinement of the top solution using default settings in phenix resulted in the following statistics.
>
> start final
> ---------------------------------------
> R-work: 0.5000 0.4003
> R-free: 0.4989 0.4586
> RMS(angles): 1.82 1.74
> RMS(bonds): 0.013 0.009
>
> I am relatively new to crystallography and would appreciate any help in understanding why I am getting multiple solutions and if there is a way to reconcile the results into a single solution.
>
> Thank you
> Abhishek
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