[phenixbb] twin refinement

Peter Zwart phzwart at gmail.com
Tue Mar 2 07:11:33 PST 2010

does xtriage suggest twinning as well?

if it doesn't you should merge in p622 and try solution/refinement again.
what does the rvsr statistic say?

the bias problem is known and due to detwinning when computing maps.
Also, make sure you choose you free set properly. Phenix does a good
job in this. ccp4 programs might not, not sure.


2010/3/2 subhash bihani <subhashbihani at gmail.com>:
> Hi
> i am refining a protein strucutre with space group P61. Intesity statistics
> doesnot suggest any twining but refmac and phenix xtriage suggest a twin
> operator  with fraction 0.48. when refined with this twin operator R factors
> come dowm by 3-5% and also map looks much better. but upon closer inspceion
> it seems that maps are heavily biased toward the model in both refmac and
> phenix ( I have mutated one lysine to his and it changed the map to cover
> his). my question is why twin refinement maps are biased and what are the
> ways to overcome this.
> my second question is how to decide whether to use twin refinement or not.
> is it depends on R factor statistics or we have to check some other
> parameters.
> thanks in advance
> subhash bihani
> scientific officer
> Bhabha Atomic Research Centre
> Trombay-400085
> Mumbai(M.S.)
> India
> Ph. +912594688 (o)
> +919322191020
> --
> Subhash Bihani
> Scientific Officer
> Solid State Physics Division
> Bhabha Atomic Research Centre
> Trombay, Mumbai-85
> Ph. 25594688 (o)
> alternate email: subhashbihani at yahoo.co.in
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P.H. Zwart
Beamline Scientist
Berkeley Center for Structural Biology
Lawrence Berkeley National Laboratories
1 Cyclotron Road, Berkeley, CA-94703, USA
Cell: 510 289 9246
BCSB:     http://bcsb.als.lbl.gov
PHENIX: http://www.phenix-online.org
CCTBX:  http://cctbx.sf.net

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