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When you tried refmac, did you also try some different models for rigid
groups using TLS ? I have seen several cases where there were reasonable
displacements which could be modeled by TLS tensors, what led to a
serious decrease on the R factors.
In my experience, even using just one TLS group per monomer has often led
to a significant (>1%) decrease in Rfree, so it's not even always
necessary to find creative ways to chop molecules into smaller groups.
Yes, amongst the "different models" I meant the "basic" one considering
each monomer separately. But it is good to reinforce that, maybe that does
not get clear. Anyway, some automation is gotten at the
http://skuld.bmsc.washington.edu/~tlsmd/index.html server.
If you haven't told REFMAC to generate all riding hydrogens, this could be
one source of the problem - at 2.0A it will probably lower your Rfree by
another 1% or more. CNS by default seems to ignore hydrogens, so I always
see a couple percent improvement when switching from CNS to REFMAC (with
hydrogens).
Yet one other point to consider.
Wu, luck and let me know if and how you succeed lowering the R-factors.
Jorge
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