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Re: [ccp4bb]: anisotropic B-factors
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> My question is a simple one.
> What resolution can we refine B-factors anisotropically from ?
> My crystal belogns to s.g. C2, two moleclues in an asymmetric unit. The
> molecular weight of each molecule which has a heme (heme B) is about 24K. V
> solvent is 0.41. The number of unique reflections is about 65000 in my data.
the answer is a simple one, too: "it depends"
probably not at a resolution worse than ~1.5 A, but use the free R-value to
decide whether or not anisotropic ADPs truly improve the model (especially
important in the "anisotropic twilight zone" of ~1.4-1.6 A; you would hope to
see a drop in Rfree of at least a couple of percentage points). of course,
this assumes that you apply it to the entire model. if you only apply it to a
small part of your model (e.g., your heme group), you cannot use Rfree to
judge the validity. in that case, you could use the real-space fit (e.g., to a
SIGMAA-weighted 2mFo-DFc map) of the entity in question instead. if you were
to do this at a resolution of ~1.4 A or worse, though, you (and a good
referee, too) would want to see a substantial improvement of the fit of said
entity to the density (both qualitatively and quantitatively)
--gerard
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Gerard J. Kleywegt
[Research Fellow of the Royal Swedish Academy of Sciences]
Dept. of Cell & Molecular Biology University of Uppsala
Biomedical Centre Box 596
SE-751 24 Uppsala SWEDEN
http://xray.bmc.uu.se/gerard/ mailto:gerard@xray.bmc.uu.se
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