Re: [ccp4bb]: about REFMAC5

["Eleanor J. Dodson" <ccp4@ysbl.york.ac.uk>]

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GUAN wrote:
> 
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> 
> I use CNS to refine a structure to R=16.99% and Rf=18.92% with
> a 1.4 A data set, and use REFMAC5 to refine anisotropic B factors,
> as suggested by many experts on CCP4 BB. The result showed a R
> of 13.11% and Rf of 16.50%.
> But an expert here said that the number of my reflections is not
> enough for this refinement, so the result was some meaningless.
> I have 19255 reflections, 132 residues and 146 waters in the A.U.,
> (total 1154 atoms). Each atom has 9 parameters to be refined
> (3 coordinate parameters and 6 anisotropic B factor parameters),
> so the ratio of reflection over parameters is about 2, not very
> high.
> so, I wonder when to refine anisotropic B factors using REFMAC5?
> what should the ratio should  be? How to tell the if the result
> is OK or meaningless?
> 
> Thanks,
> Rong-Jin Guan


 In general, any protocol which reduces both the Rfactor AND FreeRfactor
is probably a good one. You dont say what your FreeR was before starting
anisotropic refinement but it looks good now.
Of course you are not really adding 5 more free parameters per atom
because the anisotropic B factors are restrained.

 We have certainly seen real improvement in structures measured by
better electron density maps as well as lower R factors with anisotropic
B factor refinement at 1.5A. It depends to some extent on the quality
and completeness of your data - one mans 1.4A is anothers 1.2 ..
 Eleanor 
-- 
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Eleanor J.Dodson, Chemistry Department, University of York, U.K.
Tel: Home +44 (1904) 42 44 49, work:  +44 (1904) 43 25 65
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