[ccp4bb]: refinement problems

[Sean Johnson <sjj1@duke.edu>]

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I am having problems refining a structure in a new space group.  The R and
Rfree values are stuck at 27.5 % and 31.4 %, respectively.  I have been
using CNS for refinement, but I am open to any other suggestions.

Here are a few details...

The spacegroup is P3(1)21.  I have complete data to 1.95 A (99% in the
highest resolution bin).  The Rsym is ~6.5%.  The structure was solved by
molecular replacement using the same protein solved in a different space
group.

My model contains ~600 residues.  For the most part, the density looks
great.  However, there is a region of ~30 residues where the density
breaks up.  The B-factors refine to about 85 A^2 in this region (the
average overall B-factor is 45 A^2).  I have calculated composite
simulated annealing omit maps.  I also calculated a map using the prime
and switch routine in resolve.  None of these maps were helpful in
retracing the model.  I have concluded that the region is simply
disordered.  I even tried removing that region from the model and let a
solvent correction flatten it out, but there was no movement in the R
factors.

When I run Wilson scaling using Truncate, it tells me that I have
anisotropic data.

Are any of these clues helpful?  I'd be happy to hear any suggestions.  I
need to complete this structure yesterday.

Thanks,

Sean Johnson
Duke University
sjj1@duke.edu